Overview of what you should know about the different COVID-19 vaccines, including vaccine types and how they work to provide protection against COVID-19, which vaccines have been authorized and recommended in the United States, and which are in Phase 3 clinical trials.
These CDC recommendations are based on the latest public health science to inform safer, more responsible international travel during the COVID-19 pandemic. These recommendations are not intended to be requirements for the travel industry. Follow all destination and airline recommendations or requirements.
Air travel requires spending time in security lines and airport terminals, which can bring you in close contact with other people and frequently touched surfaces. Social distancing is difficult in busy airports and on crowded flights, and sitting within 6 feet of others, sometimes for hours, may increase your risk of getting COVID-19. How you get to and from the airport, such as with public transportation and ridesharing, can also increase your chances of being exposed to the virus.
Testing before and after travel can reduce the risk of spreading COVID-19. Testing does not eliminate all risk, but when paired with a period of staying at home and everyday precautions like wearing masks and social distancing, it can make travel safer by reducing spread on planes, in airports, and at destinations.
Here’s what to know:
- Get tested 1-3 days before your flight.
- Get tested 3-5 days after travel AND stay home for 7 days after travel.
- Even if you test negative, stay home for the full 7 days.
- If you don’t get tested, it’s safest to stay home for 14 days after travel.
- Always follow state and local recommendations or requirements related to travel.
- Delay your travel if you are waiting for test results.
Below is what you need to know about getting tested before your international flight.
- Get tested with a viral test 1-3 days before you depart and again 1-3 days before you return.
- Make sure you get your test results before you travel. If you are waiting for results, delay your travel.
- Do not travel if your test result is positive; immediately isolate yourself, and follow public health recommendations.
- A negative test does not mean that you were not exposed or that you will not develop COVID-19. Make sure to wear a mask, stay at least 6 feet from others, wash your hands, and watch your health for signs of illness while traveling.
- Keep a copy of your test results with you during travel. You may be asked for them.
Check if your airline requires any health information, testing, or other documents. Some destinations require testing before travel and/or after arrival. Information about testing requirements for your destination may be available from the Office of Foreign Affairs or Ministry of Health, or the US Department of State, Bureau of Consular Affairs, Country Information webpageexternal icon.
Take steps to reduce higher-risk activities for 14 days before your trip and get tested 1-3 days before you travel. This could help reduce the chance that your travel will be interrupted or delayed by COVID-19.
Get tested 3-5 days after travel AND stay home for 7 days after travel. Even if you test negative, stay home for the full 7 days. If you don’t get tested, it’s safest to stay home for 14 days. Always follow state and local recommendations or requirements related to travel.
A negative test does not mean that you were not exposed; you can still develop COVID-19. Watch for symptoms for 14 days after travel, immediately isolate yourself if you develop symptoms, and learn what to do if you are sick.
If your test is positive for COVID-19, immediately isolate yourself and follow public health recommendations. Do not travel until it is safe for you to be around others; this includes your return trip home.
You may have been exposed to COVID-19 on your travels. You may feel well and not have any symptoms, but you can be contagious without symptoms and spread the virus to others. You and your travel companions (including children) pose a risk to your family, friends, and community for 14 days after you were exposed to the virus.
Regardless of where you traveled or what you did during your trip, take these everyday actions to protect others from getting COVID-19:
- Stay at least 6 feet/2 meters (about 2 arm lengths) from anyone who did not travel with you, particularly in crowded areas. It’s important to do this everywhere — both indoors and outdoors.
- Wear a mask to keep your nose and mouth covered when you are in shared spaces outside of your home, including when using public transportation.
- If there are people in the household who did not travel with you, wear a mask and ask everyone in the household to wear masks in shared spaces inside your home for 14 days after travel.
- Wash your hands often or use hand sanitizer with at least 60% alcohol.
- Watch your health: Look for symptoms of COVID-19, and take your temperature if you feel sick.
Where do I get tested?
What kind of test should I get?
You should get a viral test that can determine if you are currently infected with COVID-19. Learn more about testing for a current infection.
What else should I do before I travel to protect myself and others from COVID-19?
- Going to a large social gathering like a wedding, funeral, or party.
- Attending a mass gathering like a sporting event, concert, or parade.
- Being in crowds like in restaurants, bars, fitness centers, or movie theaters.
- Taking public transportation like trains or buses or being in transportation hubs like airports.
- Traveling on a cruise ship or river boat.
Is one test enough to prevent spread during my travel?
CDC recommends getting tested 1-3 days before your flight AND 3-5 days after your trip AND stay home for 7 days. Even if you test negative, stay home for the full 7 days. If you don’t get tested, it’s safest to stay home for 14 days. Getting tested in combination with staying home significantly reduces travelers’ risk of spreading COVID-19.
What if I recently recovered from COVID-19?
CDC does not recommend getting tested again in the three months after a positive viral test, as long as you do not have symptoms of COVID-19. If you have had a positive viral test in the past 3 months, and you have met the criteria to end isolation, travel with a copy of your test results and a letter from your doctor or health department that states you have been cleared for travel.
Information for School Nurses and Other Healthcare Personnel (HCP) Working in Schools and Child Care Settings
School nurses and other healthcare personnel (HCP) play an important role in opening schools and child care programs for in-person learning and other in-person activities and keeping them open during the COVID-19 pandemic. School nurses and other HCP will likely be evaluating children for symptoms or exposures, assisting administrators and teachers in implementing mitigation strategies, assisting with contact tracing, maintaining school-based clinics, assisting in school-based testing strategies, and supporting students, families, and staff. The information and resources below can help in performing these new roles and responsibilities during the COVID-19 pandemic. Resources for self-care are also included.
COVID-19 and Children
While fewer children had been reported to have COVID-19 compared with adults in the United States during the pandemic, the number of children and adolescents with COVID-19 has been increasing since early in the pandemic. Children can be infected with the virus that causes COVID-19 (SARS-CoV-2), can get sick with COVID-19, and can spread the virus to others. Most children infected with the virus that causes COVID-19 have mild symptoms and some have no symptoms at all. Some children can get severely ill from COVID-19, which means they might require hospitalization, intensive care, a ventilator, or might even die. The symptoms of COVID-19 are similar in adults and children and can look like other common illnesses, like colds, strep throat, influenza, or allergies. For more information about influenza, visit Influenza Information for Health Professionals and The Difference Between Flu and COVID-19.
Children with underlying medical conditions are at increased risk for severe illness from COVID-19. Additionally, some children may develop the rare but serious condition associated with COVID-19 called Multisystem Inflammatory Syndrome in Children (MIS-C). For more information, visit Pediatric Healthcare Providers.
Mitigation Strategies for Schools and Child Care Settings
Mitigation strategies should be layered, using many at the same time, to prevent the spread of the virus that causes COVID-19. The key mitigation strategies for schools are:
For information on protecting school staff, visit Protecting School Staff from COVID-19.
Quarantine, Isolation, Symptom Screening, and Testing for Children
Quarantine and isolation are public health practices used to prevent exposure to people who have or may have a contagious disease. Quarantine keeps someone who was exposed to the virus away from others for the duration of the incubation period (14 days), and isolation keeps someone who is infected with the virus away from others for the duration the infectious period (10 days).
CDC does not currently recommend that schools conduct symptom screenings for students, but parents or caregivers should be strongly encouraged to monitor their children for signs of infectious illness every day. Students who are sick should not attend school in-person. For more information on symptom screening, what to do if a student has symptoms of COVID-19, and when that student can return to in-person school, visit Symptom Screening in Schools.
CDC recommends testing for people with any signs or symptoms of COVID-19 and for all close contacts of persons with COVID-19. For more information, visit Overview of Testing for HCP, information for Pediatric Healthcare Providers, and Considerations for Testing in K-12 Schools.
Contact Tracing in Schools
Contact tracing is essential to prevent the spread of the virus that causes COVID-19. Contact tracing is the process of notifying people (contacts) of their potential exposure to the virus that causes COVID-19, providing information about the virus, providing instructions for quarantine and symptom monitoring, and referring to testing, clinical services, and other services as needed. School nurses and other HCP in schools and child care settings may be asked to help administrators and public health officials with contact tracing. For more information, visit Case Investigation and Contact Tracing in Schools and discuss with your public health officials.
Infection Prevention Recommendations for School Nurses and Other HCP Providing Care
School nurses and other HCP in schools and child care settings should follow the Infection Prevention and Control Recommendations for Healthcare Personnel when providing direct patient care.
- Nurses and other HCP should use all recommended personal protective equipment (PPE) when providing direct care to someone with confirmed or suspected COVID-19, including use of N95, or equivalent respirator (or face mask if unavailable), gown, gloves, and eye protection.
- In addition to following standard precautions like hand hygiene and disinfection, nurses and other HCP should use a facemask and eye protection when caring for students who are not suspected to be have COVID-19 when there is moderate or substantial community transmission. Facemasks are preferred over cloth masks for all HCP.
- If there are shortages of PPE, nurses and other HCP should review CDC’s guidance for Optimizing PPE Supplies and can consider using the same respirator or facemask throughout the entire shift.
- For information on how to safely put on and take off PPE, visit Using PPE.
- For information on what to do if a nurse or other HCP is exposed to a person with the virus that causes COVID-19, visit Guidance for Risk Assessment and Work Restrictions for HCP. For information on when a nurse or HCP can return to work after having COVID-19, visit Return to Work for HCP.
- For information on providing nebulizer treatments in schools and other considerations for asthma treatments in schools, visit FAQs for Schools.
Providing Services in Clinic and Through Telehealth
For nurses and other HCP working in clinics that provide in-person services, visit Get your Clinic Ready for COVID-19. For nurses and HCP providing telehealth services, visit Using Telehealth during the COVID-19 Pandemic.
Supporting Students and Staff
School staff and other trusted adults can play an important role in helping children make sense of what they hear in a way that is honest, accurate, and minimizes anxiety or fear. For tips and discussion topics, visit Talking to Children about COVID-19. CDC has additional resources like Helping Children Cope and Support for Teens.
The pandemic has been stressful for many people. For toolkits and more resources for adults, visit Stress and Coping and How Right Nowexternal icon. For information about coping with stress for staff in the workplace, visit Coping with Stress for Employees and Managing Workplace Fatigue During COVID-19.
Self-Care for Nurses and other Healthcare Personnel
Providing care to others during the COVID-19 pandemic can lead to stress, anxiety, fear, and other strong emotions. How you cope with these emotions can affect your well-being, the care you give to others while doing your job, and the well-being of the people you care about outside of work. For information on coping with stress during the pandemic, visit HCP and First Responders: How to Cope with Stress. For nurses and other HCP who are experiencing stress and burnout, the National Crisis Support Hotlines and Directoriespdf iconexternal icon has resources that can help. For more information on self-care, view the Self-Care for Healthcare Workers Modulespdf iconexternal icon.
For considerations on maintaining daily life during the pandemic, visit Daily Activities.
For the latest information on COVID-19 from CDC, visit CDC’s COVID-19 Website.
1Indicators and data sources may be tailored to align with the context of the intended evaluation and local communities, including what is important and feasible to assess and what data are available. Some data may be available at the local level and may not need to be collected from child care programs independently. It is critical to maintain confidentiality and privacy of the child, staff member, or volunteer as required by the Americans with Disabilities Act and the Family Education Rights and Privacy Act.
2For indicators related to COVID-19 Epidemiology, Community Characteristics, Healthcare Capacity, and Public Healthcare Capacity being tracked, refer to existing data sources: CDC COVID Data Tracker or https://www.cdc.gov/coronavirus/2019-ncov/php/open-america/surveillance-data-analytics.html as well those being monitored in your state/local jurisdiction.
3Ensure the data collection tools and sources used to assess these indicators adequately capture data prior to and following mitigation strategy implementation to ensure changes are attributable to the mitigation strategies. Ensure other environmental and contextual factors are taken into account that may have an impact on these indicators. It is important to establish a process to collect this information that can be used to compare to previous data and to monitor for changes in social/behavioral/mental health markers moving forward.
4The National Survey of Children’s Health (NSCH)external icon provides rich data on multiple, intersecting aspects of the lives of children (ages 0-17 years)—including physical and mental health, access to quality health care, and the child’s family, neighborhood, school, and social context. The most recent year of available data is 2018.
5Disclaimer: This data source is provided as an example and does not constitute an endorsement of the entity or its guidance or policies by CDC or the federal government. CDC is not responsible for the content of the individual organization sites listed in this document.
6National Health Interview Survey (NHIS) is used to monitor progress towards national health objectives; evaluate health policies and programs; and track changes in health behaviors and health care use. NHIS includes a Sample Child questionnaire, which collects information on health status, health care services, and health behaviors of children under the age of 18 years. The most recent year of available data is 2018.
Welcome and thank you for being here today. My name is [your name] and I will be the moderator for today’s discussion. I am an [insert role] at [organization or agency name]. The purpose of this discussion is to get feedback on the prevention strategies your school implemented to reduce the spread of COVID-19. Prevention strategies are actions that people and communities, such as K-12 schools, can take to reduce the spread of the SARS-CoV-2 virus that causes COVID-19. Some examples of these prevention strategies for COVID-19 are handwashing, physical distancing (you may have heard of social distancing) and wearing a mask.
Your experience and opinions are very important to us. We are especially interested in learning about the prevention strategies implemented at [your school district or school name], the factors that helped or didn’t help your school in implementing these strategies, and how these strategies may have impacted student’s health (including social, behavioral, and mental) and academic achievement at your school.
The format we are using is a focus group that will take no more than [X minutes]. A focus group is a conversation that focuses on specific questions in an environment that is safe from the influence and judgement of others. I will guide the conversation by asking questions that each of you can respond to. There are no right or wrong answers to these questions. Just be honest. You do not have to answer any questions that you do not feel comfortable answering. If you like, you can also respond to each other’s comments. It is my role to make sure everyone gets to participate. [Notetaker’s name] is here to take notes and keep track of the time. We would like to record this focus group. The recording will not be heard by anyone outside of this project. The recording will only be used to make sure [notetaker’s name] notes are correct.
Before we get started, I want to let you all know the information that we learn today will be compiled into a final report. The report will include a summary of your comments and some recommendations. It may be shared with the Superintendent, other district leaders, or public health professionals. This focus group is anonymous and confidential. “Anonymous” means that we will not be using your names and you will not be identified as an individual in our report of this project. “Confidential” means that what we say in this room should not be repeated outside of this room. Although we hope everyone here honors this confidentiality, please remember that what you say here today could be repeated by another focus group member. So please, do not say anything that you absolutely need to keep private. The tape this interview is recorded on will be kept safely in a locked facility until it is transcribed word for word, and then it will be destroyed. May we have everyone’s permission to record this focus group? (Note to moderator: Please obtain a yes from all focus group participants before proceeding. If participant declines permission to record but is willing to participate, the session will not be recorded; however, notes will be taken. Reassure the participants that the notes will not include their names or any other information to reveal their identity.)
Thank You. There are a few ground rules to follow during our focus group. Focus Group ground rules:
- The most important rule is that only one person speaks at a time. There may be a temptation to jump in when someone is talking, but please wait until they have finished.
- There are no right or wrong answers.
- You do not have to speak in any particular order.
- When you do have something to say, please do so. You can raise your hand to speak or speak up after the other person has finished speaking. There are many of you in the group and it is important that I obtain each of your views.
- You do not have to agree with the views of other people in the group.
Does anyone have any questions before we begin?
This interview guidepdf icon is meant to be adaptable for your local context. This tool is meant to help the interviewer obtain more in-depth information about perceptions and experiences of mitigation strategies used to reduce the spread of COVID-19 when schools are in in-person learning mode. The tool is intended for government professionals in public health or education, school district administrators, and administrators of K-12 schools who are interested in conducting their own data collection. It may also be adapted to other settings. Local Institutional Review Board (IRB) guidelines should be explored and implemented as required prior to conducting interview activities/or data collection activities. Potential interviewees could include school or school district administrators, school faculty and staff, school-age children, or parents or guardians of school-age children. Interviews can be conducted by phone, virtually, or in person (ensuring appropriate COVID-19 prevention strategies are in place).
Depending on your needs and local context, you should select the questions provided in this interview guide that are most relevant to the questions you have identified and the in-depth information you are seeking from participants about their perceptions and experiences of mitigation strategies.
- The tool can be adapted for these different audiences. For example, parents may not be aware of all prevention strategies implemented in their child’s school so the interviewer would want to adapt this question accordingly.
- The specificity of the interview guide will depend on the purpose of the interview, the sociodemographic characteristics (e.g., age, gender, race and ethnicity, education level, and income) of the interviewees, and type of interview.
- Not all the interview questions are relevant for all potential interviewees. The questions might be developed or modified for different audiences and presented in separate formats.
You can add, remove, or change the interview questions below to align with the purpose of the interview and your evaluation questions, and to fit within the time allotted to conduct the interview.
Thank you for agreeing to participate in this [telephone, virtual, or in-person] interview. My name is [your name]. I am an [insert role] at [organization or agency name]. The purpose of this interview is to help us get feedback on the prevention strategies your school implemented to reduce the spread of COVID-19. Prevention strategies are actions that people and communities, such as, K-12 schools, can take to reduce the spread the SARS-CoV-2 virus that causes COVID-19. Some examples of these prevention strategies for COVID-19 are handwashing, physical distancing (you may have heard of social distancing) and wearing a mask.
Your experience and opinions are very important to us. We are especially interested in learning about the prevention strategies implemented at [your school district or school name], the factors that helped or didn’t help your school in implementing these strategies, and how these prevention strategies may have impacted student’s health (including social, behavioral, and mental) and academic achievement at your school.
The interview should take no more than [X minutes]. An interview is a guided conversation where the interviewer asks specific questions and actively listens to the interviewee. There are no right or wrong answers to these questions. Just be honest. You do not have to answer any questions that you do not feel comfortable with. [Notetaker’s name] is here to take notes and keep track of time. We would like to record this interview. The recording will not be heard by anyone outside of this project. The interview is being recorded so that we can fully capture your experience and opinions.
Before we get started, I want to let you know that the information that we learn today will be compiled with other interviews into a final report. The report will include a summary of your comments and some recommendations. It may be shared with the Superintendent, other district leaders, or public health professionals. What you say is confidential, and your name or the name of others will not be used in any reporting. This interview is anonymous and confidential. “Anonymous” means that we will not be using your name and you will not be identified in our report. If, during the interview, you mention other people, we will not use their names and they will not be identified in our report either. “Confidential” means that what we say in this room should not be repeated outside of this room. The tape this interview is recorded on will be kept safely in a locked facility until it is transcribed word for word, and then it will be destroyed. May we have your permission to record this interview?
(Note to interviewer: Please obtain a yes from participant before proceeding. If participant declines permission to record but is willing to participate, the session will not be recorded; however, notes will be taken. Reassure the participant that the notes will not include their name or any other information to reveal their identity.)
Thank you. What questions do you have before we begin?
(Instruction for notetaker: begin taking notes on the interview as the interviewer asks the following questions)
I would like to give you a few minutes to think about your experiences with changes that were made in [your school district, school, or classroom] to reduce the spread of COVID-19. We’ll talk about these as ‘prevention strategies’ (Note to interviewer: consider offering a brief overview of mitigation strategies that can help participants better understand the mitigation strategies that may be discussed and the implementation of such prevention strategies.)
- What prevention strategies were implemented in [your school district, school, or classroom] to reduce or prevent the spread of COVID-19? (Notes to interviewer: prompt if don’t hear anything about the following categories: masks, physical/social distancing, keeping students in a group throughout the day (cohorts or pods), screening for symptoms at home or in school, changes to meal service, washing hands or using hand sanitizer, changes to extracurricular activities including sports)
- How were the prevention strategies implemented in [your school district, school, or classroom]?
- When were the prevention strategies implemented in [your school district, school, or classroom]?
- In your opinion, how well did [students, teachers, staff] follow or practice these prevention strategies?
- In your opinion, what strategies were the easiest for [students, teachers, or staff] to implement?
- What made them easy?
- In your opinion, what strategies were the hardest for [students, teachers, or staff] to implement?
- What made them hard?
- In your opinion, what strategies were the easiest for [students, teachers, or staff] to implement?
- What are your school plans for when a [student, teacher, or staff] has been diagnosed by a doctor with COVID-19 or suspected to have COVID-19?
- Is there a designated area where students, teachers, or staff with symptoms of COVID-19 are asked to wait until they can go home?
- Is there a number of days [students, teachers, or staff] with suspected or confirmed COVID-19 are asked to stay home from school? (Note to Interviewer: Ask the interviewee to answer the best they can.)
- To the best of your knowledge, does the [school district or school] try to notify people who came into contact with an individual who has been diagnosed with COVID-19?
- How did the [school district or school] communicate prevention strategies to [students, parents, teachers, and staff]?
- What were the messages the [school district or school] communicated to [students, parents, teachers, and staff]?
- In your opinion, were these messages helpful in communicating prevention strategies?
- What was it about these messages that made them helpful?
- What was it about these messages that made them not helpful?
- What else can be done to help prevent COVID-19 in [your school district, school, or classroom]?
Next, I would like to hear about things that may have helped or hindered your ability to implement the prevention strategies in [your school district, school, or classroom] to reduce the spread of COVID-19.
- What did you find to be helpful when implementing the prevention strategies in [your school district, school, or classroom]?
- What were the challenges that [you or your school] encountered when implementing the prevention strategies in [your school district, school, or classroom]?
- What may have led to these challenges?
- Were these challenges resolved? If so, how? If not, what prevented these challenges from being resolved?
- What would have helped prevent the challenges?
- What trainings or resources were provided to help [students, teachers, or staff] implement the prevention strategies to reduce spread of COVID-19? (Notes to interviewer: This could include technology, excused absences, etc.)
- What resources provided by [school district or school] were most helpful?
- What resources provided by the [school district or school] were not helpful?
- What is missing that may have been helpful for successful implementation?
- How did the [school district] support the implementation of the prevention strategies?
- What changes have been made to the prevention strategies since the start of the school year?
- To the best of your knowledge, what factors contributed to [your school district or school] decisions to reduce or expand COVID-19 prevention strategies over [time period; e.g., fall 2020]?
- How well do you think [your school district, school, or classroom] did in working to prevent or reduce the spread of COVID-19?
- What do you think [your school district, school, or classroom] could have done differently to reduce or prevent the spread of COVID-19?
Next, I would like to hear your opinions about the impact of the prevention strategies on [student, teachers, and staff] health (social, behavioral, and mental) and academic achievements.
- How would you describe any impact the prevention strategies have had on reducing the spread of COVID-19 in your [school district or school] among [students, families, teachers, or staff members]?
- How many [students, teachers, or staff] have been diagnosed by a medical professional with COVID-19 in [specify time period, e.g., fall 2020]? (Note to Interviewer: Ask the interviewee to answer the best they can.)
- How many [students, teachers, or staff] believed they had COVID-19, but did not get a COVID-19 test? (Note to Interviewer: Ask the interviewee to answer the best they can.)
- During the school year, were there any increases of COVID-19 among [students, teachers, or staff] who knew each other? (Note to Interviewer: Ask the interviewee to answer the best they can)
- How many days was the school shut down [specify time period, e.g., spring or fall 2020] because of COVID-19? (Note to Interviewer: Ask the interviewee to answer the best they can.)
- What differences did you observe in academic outcomes among students? (Notes to interviewer: This could include student grades, level of engagement in class, comprehension of the material, and other similar outcomes.)
- How do you think fall 2020 academic outcomes compare with fall 2019 at the [school or classroom level]?
- How would you describe any impact the prevention strategies have had on social health outcomes (e.g., treating others with respect or developing and maintaining friendships with peers) among [students, teachers, or staff members]?
- How would you describe any impact the prevention strategies have had on behavioral health outcomes (e.g., bullying, fighting, or defiance of practicing prevention strategies) among [students, teachers, or staff members]?
- How would you describe any impact the prevention strategies have had on mental health outcomes (e.g., anxiety, sadness, frustration, or anger) among [students, teachers, or staff members]?
- How have the prevention strategies affected different populations or groups?
Lastly, I have a few more questions for you about future implementation of prevention strategies.
- What are your overall suggestions for improving the implementation of prevention strategies in [your school district, school, or classroom]?
- What advice would you give to [teachers or other schools]?
- Do you have any other thoughts or comments you would like to share?
Thank you so much for sharing this useful information with us. Today, we have learned [summarize interview information]. I would like to remind you that any information you provided is anonymous and confidential. If you have any questions or concerns about today’s interview, please contact me at [provide contact information].
The identification of the novel coronavirus SARS-CoV-2 in December 2019 has led to a growing and continually evolving body of knowledge about the virus and the disease it causes, COVID-19.
In peer-reviewed literature and public discussion, persistent symptoms are being reported among COVID-19 survivors, including individuals who initially experience a mild acute illness. These persistent symptoms pose new challenges to patients, healthcare providers, and public health practitioners. The natural history of SARS-CoV-2 infection and COVID-19 is a current area of investigation, and the prevalence, type, duration, and severity of persistent symptoms following resolution of acute SARS-CoV-2 infection, as well as risk factors associated with their development, are currently being studied.
While older patients may have an increased risk for severe disease, young survivors, including those physically-fit prior to SARS-CoV-2 infection, have also reported symptoms months after acute illness (Assaf, Asthma UK and British Lung Foundation, Godlee). Research is underway to differentiate symptoms of a prolonged course of COVID-19 illness from sequelae following resolution of acute SARS-CoV-2 infection, achieve consensus on the time period at which to define the post-acute and long-term phases of COVID-19, and distinguish health effects exclusively related to infection with SARS-CoV-2 from consequences of procedures and treatments required for care of persons with severe disease of any etiology.
Characterization of the etiology and pathophysiology of late sequelae is underway, and may reflect organ damage from the acute infection phase (Ngai), manifestations of a persistent hyperinflammatory state (Yende, Tay), ongoing viral activity associated with a host viral reservoir (Hartley), or an inadequate antibody response (Wu). Factors in addition to acute disease that may further complicate the picture include physical deconditioning (Gemelli) at baseline or after a long disease course (Thornton), pre-COVID-19 comorbidities (O’Keefe), and psychological sequelae following a long or difficult disease course (Yende) as well as those relating to lifestyle changes due to the pandemic (Galea). Likely, the persistent sequelae of COVID-19 represent multiple syndromes resulting from distinct pathophysiological processes along the spectrum of disease.
Though there is limited information on late sequelae of COVID-19, reports of persistent symptoms in persons who recovered from acute COVID-19 illness have emerged (Tenforde, Carfi, Halpin, COVID Symptom Study, Greenlaugh, del Rio). The most commonly reported symptoms include fatigue, dyspnea, cough, arthralgia, and chest pain (Tenforde, Halpin, O’Keefe, Calfi, Assaf, Banda, Lambert). Other reported symptoms include cognitive impairment, depression, myalgia, headache, fever, and palpitations (Tenforde, Halpin, O’Keefe, Calfi, Assaf, Banda, Lambert). More serious complications appear to be less common but have been reported. These complications include:
- Cardiovascular: myocardial inflammation, ventricular dysfunction (Sardari, Puntmann, Rajpal)
- Respiratory: pulmonary function abnormalities (Huang, Zhao)
- Renal: acute kidney injury (Peleg)
- Dermatologic: rash, alopecia (Lambert)
- Neurological: olfactory and gustatory dysfunction, sleep dysregulation, altered cognition, memory impairment (Otte, Paderno, Halpin, Lambert, Assaf, Banda)
- Psychiatric: depression, anxiety, changes in mood(Halpin, Lambert, Singh)
Post-COVID-19 care centers are opening at academic medical centers in the United States, bringing together multidisciplinary teams to provide a comprehensive and coordinated treatment approach to COVID-19 aftercare. The National Institutes of Health have published interim guidelines for the medical management of COVID-19external icon, including a section on persistent symptoms or illnesses after recovery from acute COVID-19. These guidelines will be updated as new information emerges. Survivor support groups are connecting individuals, providing support, and sharing resources with survivors and others affected by COVID-19 (Body Politic, Survivor Corps). Multi-year studies will be crucial in elucidating longer-term sequelae. CDC continues active investigation into the full spectrum of COVID-19 to establish a more complete understanding of the natural history of SARS-CoV-2 infection and COVID-19 related illnesses, which can inform care strategies as well as the public health response to this virus.
Disease surveillance and laboratory detection are at the heart of CDC’s mission and fundamental to the COVID-19 public health response. They underpin CDC’s work with federal, state, tribal, local, and territorial (STLT), academic, and commercial partners to better understand the burden of COVID-19 disease and efforts to mitigate its diverse impacts, including the disproportionate impacts of COVID-19 on people at increased risk for health disparities and inequities. CDC supplements surveillance and laboratory methods with the modern tools of viral genomics and mathematical modeling.
Objective 1. Develop new, or modify existing, methods of epidemiologic surveillance for COVID-19
CDC has established multiple systems of surveillance to monitor trends in COVID-19 disease in the United States and measure the impact of interventions. Surveillance studies are helping to estimate the proportion of cases that are asymptomatic or mild versus those that are severe or fatal. A key priority is the development, implementation, and evaluation of innovative, targeted strategies to rapidly detect early signals of COVID-19 in communities or settings of special interest such as schools, workplaces, or congregate living facilities.
CDC is utilizing serology testing to better understand how many infections with SARS-CoV-2 have occurred at different points in times in different locations. Seroprevalence surveys include large-scale geographic surveys, community level surveys, and smaller-scale surveys focusing on specific populations such as healthcare workers.
Surveillance strategies in international settings may include adaptation of established disease testing systems for other diseases (e.g., human immunodeficiency virus [HIV]) and leveraging existing partnerships (e.g., polio eradication programs).
Objective 2. Develop and optimize testing for SARS-CoV-2
Identifying new detection methods and strategies that improve the speed, accuracy, and sensitivity of diagnostics and are not reliant on reagents that can limit testing are a high priority.
CDC is pursuing multiple lines of research including evaluation of different types of specimens, assays, and serial testing strategies to optimize detection of acute and past SARS-CoV-2 infection; development of rapid, point-of-care diagnostic tests and multiplex testing systems to concurrently detect SARS-CoV-2 and influenza A and B; and identification of the most useful assays to advance understanding of community levels of protection needed to interrupt transmission (i.e., herd immunity). Determining the optimal testing approach to differentiate natural infection from vaccination and developing other laboratory tools are essential to support the development and monitoring of COVID-19 vaccines.
CDC is continuing its work with the U.S. Food and Drug Administration and the National Institutes of Health to validate tests produced by commercial labs and other entities.
Objective 3. Utilize viral genomics to advance understanding of COVID-19 and mitigate its impact
CDC is using genomic sequencing to investigate the evolution, emergence, and spread of COVID-19 infections in communities and defined populations. Incorporation of viral genomic data with patient genomic, clinical, and epidemiologic data can lead to a better understanding of patient risk factors, clinical outcomes, and transmission dynamics. CDC, through its establishment of a new national viral genomics consortium,3 is accelerating the release of SARS-CoV-2 sequence data into the public domain.
Large-scale sequencing studies to monitor the genetic diversity and stability of SARS-CoV-2 have the potential to offer clues on the impact of new virus variants on diagnostics, therapeutic agents, and vaccines.
Objective 4. Use mathematical modeling and other technological tools to forecast COVID-19 trends and measure the impact of interventions across a range of populations
Mathematical modeling is an important tool to help inform public health decision making. CDC, working with academic groups, uses probabilistic models to forecast the timing and trajectory of COVID-19 infections; the demand for hospital-based services; and deaths at the national, state, and sub-state levels. Models to forecast the impact of therapeutics, testing, vaccine, and mitigation strategies are also a priority.
Novel technological tools such as cell phone mobility data, for example, when used in combination with social, behavioral, and ethnographic information, offer the potential to assess the impact of community mitigation efforts, but require a thorough assessment of their practical utility.
Objective 5. Assess and limit the impact of the COVID-19 response on healthcare services and public health programs in domestic and international settings
The COVID-19 pandemic is affecting people’s healthcare seeking behaviors for routine preventive and medical care. CDC is working with domestic and international clinical and public health partners to assess pandemic-related impacts on healthcare, special-needs care, routine public health activities, and priority disease elimination/control programs such as HIV, tuberculosis (TB), and neglected tropical diseases. Findings from these studies can be used to identify the best strategies and policies to maintain access to care, treatment, and preventive services with a focus on populations at increased risk for health disparities and inequities.
SARS-CoV-2 infection is transmitted predominately by respiratory droplets generated when people cough, sneeze, sing, talk, or breathe. CDC recommends community use of masks, specifically non-valved multi-layer cloth masks, to prevent transmission of SARS-CoV-2. Masks are primarily intended to reduce the emission of virus-laden droplets (“source control”), which is especially relevant for asymptomatic or presymptomatic infected wearers who feel well and may be unaware of their infectiousness to others, and who are estimated to account for more than 50% of transmissions.1,2 Masks also help reduce inhalation of these droplets by the wearer (“filtration for personal protection”). The community benefit of masking for SARS-CoV-2 control is due to the combination of these effects; individual prevention benefit increases with increasing numbers of people using masks consistently and correctly.
Source Control to Block Exhaled Virus
Multi-layer cloth masks block release of exhaled respiratory particles into the environment,3-6 along with the microorganisms these particles carry.7,8 Cloth masks not only effectively block most large droplets (i.e., 20-30 microns and larger)9 but they can also block the exhalation of fine droplets and particles (also often referred to as aerosols) smaller than 10 microns ;3,5 which increase in number with the volume of speech10-12 and specific types of phonation.13 Multi-layer cloth masks can both block up to 50-70% of these fine droplets and particles3,14 and limit the forward spread of those that are not captured.5,6,15,16 Upwards of 80% blockage has been achieved in human experiments that have measured blocking of all respiratory droplets,4 with cloth masks in some studies performing on par with surgical masks as barriers for source control.3,9,14
Filtration for Personal Protection
Studies demonstrate that cloth mask materials can also reduce wearers’ exposure to infectious droplets through filtration, including filtration of fine droplets and particles less than 10 microns. The relative filtration effectiveness of various masks has varied widely across studies, in large part due to variation in experimental design and particle sizes analyzed. Multiple layers of cloth with higher thread counts have demonstrated superior performance compared to single layers of cloth with lower thread counts, in some cases filtering nearly 50% of fine particles less than 1 micron .14,17-29 Some materials (e.g., polypropylene) may enhance filtering effectiveness by generating triboelectric charge (a form of static electricity) that enhances capture of charged particles18,30 while others (e.g., silk) may help repel moist droplets31 and reduce fabric wetting and thus maintain breathability and comfort.
Human Studies of Masking and SARS-CoV-2 Transmission
Data regarding the “real-world” effectiveness of community masking are limited to observational and epidemiological studies.
- An investigation of a high-exposure event, in which 2 symptomatically ill hair stylists interacted for an average of 15 minutes with each of 139 clients during an 8-day period, found that none of the 67 clients who subsequently consented to an interview and testing developed infection. The stylists and all clients universally wore masks in the salon as required by local ordinance and company policy at the time.32
- In a study of 124 Beijing households with > 1 laboratory-confirmed case of SARS-CoV-2 infection, mask use by the index patient and family contacts before the index patient developed symptoms reduced secondary transmission within the households by 79%.33
- A retrospective case-control study from Thailand documented that, among more than 1,000 persons interviewed as part of contact tracing investigations, those who reported having always worn a mask during high-risk exposures experienced a greater than 70% reduced risk of acquiring infection compared with persons who did not wear masks under these circumstances.34
- A study of an outbreak aboard the USS Theodore Roosevelt, an environment notable for congregate living quarters and close working environments, found that use of face coverings on-board was associated with a 70% reduced risk.35
- Investigations involving infected passengers aboard flights longer than 10 hours strongly suggest that masking prevented in-flight transmissions, as demonstrated by the absence of infection developing in other passengers and crew in the 14 days following exposure.36,37
Seven studies have confirmed the benefit of universal masking in community level analyses: in a unified hospital system,38 a German city,39 a U.S. state,40 a panel of 15 U.S. states and Washington, D.C.,41,42 as well as both Canada43 and the U.S.44 nationally. Each analysis demonstrated that, following directives from organizational and political leadership for universal masking, new infections fell significantly. Two of these studies42,44 and an additional analysis of data from 200 countries that included the U.S.45 also demonstrated reductions in mortality. An economic analysis using U.S. data found that, given these effects, increasing universal masking by 15% could prevent the need for lockdowns and reduce associated losses of up to $1 trillion or about 5% of gross domestic product.42
Experimental and epidemiological data support community masking to reduce the spread of SARS-CoV-2. The prevention benefit of masking is derived from the combination of source control and personal protection for the mask wearer. The relationship between source control and personal protection is likely complementary and possibly synergistic14, so that individual benefit increases with increasing community mask use. Further research is needed to expand the evidence base for the protective effect of cloth masks and in particular to identify the combinations of materials that maximize both their blocking and filtering effectiveness, as well as fit, comfort, durability, and consumer appeal. Adopting universal masking policies can help avert future lockdowns, especially if combined with other non-pharmaceutical interventions such as social distancing, hand hygiene, and adequate ventilation.