Ask SciMoms: Why did CDC mask recommendations change again?

On July 27, 2021,  the Centers for Disease Control and Prevention (CDC) updated their masking and other recommendations to help mitigate the spread of SARS-CoV-2. This post will discuss why the recommendations have changed, review the current CDC masking guidelines, and compare the guidelines to masking recommendations from other organizations and countries. 

Why do CDC mask recommendations keep changing? 

CDC updated recommendations because the science has shown that the delta variant has changed the dynamics of the SARS-CoV-2 virus. Delta is more contagious, and many people remain at risk because too many people remain unvaccinated and vulnerable to the virus. Vaccines are still thought to be around 90% effective at protecting us against severe disease and death, but vaccine effectiveness may be lower against transmission. This means that some vaccinated individuals will become infected and could possibly spread the virus to others. However, the data show that those most at risk of being infected and spreading the virus are those who remain unvaccinated. Because a significant percentage of the US remains unvaccinated and at risk, it is critical to take steps to mitigate the spread of the delta variant. The CDC did not think these steps were necessary before the delta variant became dominant in the United States, but new data has changed that decision. One important step to slow the spread of delta is a return to masking. 

Masks and other protective recommendations change because we are dealing with a novel virus, SARS-CoV-2. Scientists worldwide and at the CDC make the best recommendations they can with the scientific information they have at the time.  It might come as a surprise, but experts expected that guidelines would continually change as we learned more about the virus. When new scientific information is discovered, recommendations must change to reflect this new info. 

What are the current CDC mask recommendations in the USA?

If you or your loved one is unvaccinated or partially vaccinated the CDC recommends masking in all public places. This recommendation includes unvaccinated children above the age of two, unless they have a medical condition that prohibits their use. This recommendation has not changed. Simple ways to remember what unvaccinated people should be doing in public settings or when gathering with people outside your own household are: 

  • Practice the 3Ws (wear a mask, watch your distance, and wash your hands)
  • Follow the two out of three rule 

You can read more about these in the previous SciMoms COVID FAQ on masks

In May, the CDC had recommended that vaccinated people could unmask in public settings. (Read about SciMoms’ concerns with the May updates here.) However, as of July 27th, 2021 the CDC recommends that vaccinated people mask in areas of substantial or high transmission, (you can check data for your area at the CDC COVID Data Tracker). They also state that regardless of transmission rate, you should consider masking if you are high risk or immunocompromised, or if you live with someone high risk, immunocompromised, or unvaccinated. This includes living with unvaccinated children.

If you are outdoors, masking is recommended for crowded settings where you may be in close contact with other individuals. If you’re outdoors with vaccinated individuals or with ample space, you can consider your risk tolerance level when deciding whether to wear a mask. The two out of three rule is a simple way to think about these situations and figure out whether you need a mask.

The American Medical Association and the Infectious Disease Society of America have both released statements supporting this decision by the CDC, and agree that the spread of the delta variant means masking is again necessary to help curb the spread of SARS-CoV-2.

What are the CDC mask recommendations for K-12 schools? 

The CDC recommends that all students, faculty, staff, and visitors at K-12 schools wear a mask, regardless of vaccination status. The American Academy of Pediatrics (AAP) also recommends universal masking for all individuals inside of K-12 schools. The reasons for this include: many of our students do not yet have access to vaccines, difficulties in verifying vaccination status, low community vaccination rates, and concerns about more transmissible SARS-CoV-2 variants. 

Both the CDC and AAP agree that in-person schooling should be prioritized, but that we must work to do this safely. Masking is a key component, combined with other layers of protection, to ensure schools can safely remain open. The goal of these recommendations is to ensure that ALL students have access to full-time in person learning. 

What are the current mask recommendations from the World Health Organization (WHO)?

The WHO has consistently recommended that everyone continue to wear a mask indoors regardless of vaccination status. This policy is different from the CDC because the WHO recommends policies for the whole world. Rates of vaccination and viral spread vary dramatically from region to region. Thus, the WHO needs to be conservative and recommend the policies that apply to the most vulnerable of the countries they serve. There are not enough people vaccinated worldwide to curb the spread of SARS-CoV-2 globally without additional mitigation measures. But we are also finding out the hard way that even in highly vaccinated countries like Israel, and highly vaccinated areas within the US like San Francisco and NY, currently experiencing large surges, we still don’t have high enough vaccination rates to curb the spread without additional mitigation measures.

Are there other countries that still have their citizens wear a mask? 

It is easy to feel alone during this pandemic and wonder if your country is making the right decision, but there are many countries besides the USA that still require or recommend masks. Current CDC mask recommendations align with recommendations in many other countries.

In Ireland, it is law to wear masks on public transport, in shops, and in other public indoor settings. Kenya also mandates masking in public. In the UK, it is recommended that people wear masks on public transit and in crowded areas. Japan also recommends masking. In Italy, it is mandatory to have your masks with you and to wear them in indoor places that are not private residences. There are many other countries that could be listed here. None of us are alone in our fight to end the COVID-19 pandemic. Masking is one important tool many countries are utilizing.

How do we know that masks work?

Masking to slow the spread of SARS-CoV-2 is new because the virus is new. However, masking to help control the spread of other pathogens, including other coronaviruses and other respiratory viruses, has been used for centuries. In 1910 Wu Lien Teh helped conduct experiments that showed that cloth masks could help slow the spread of the plague. Since then, masking has been a common mitigation measure used in a variety of settings. Data show that masking does work to help control the spread of many respiratory viruses.

  • There are trials that looked at the benefit of masking and other mitigation measures, like handwashing, to slow the spread of the flu. Results demonstrated that these mitigation measures worked to slow flu transmission (1, 2 and 3).
  • Another study showed that face masks could reduce the amount of viral RNA detected in respiratory droplets in people infected with the flu or a coronavirus that causes the common cold. 
  • A randomized control trial also looked at masking to control the spread of respiratory viruses, they found that adherence to mask wearing was low. However, when worn correctly, they were highly effective. 
  • Controlled laboratory studies demonstrate that masks can help block the spread or inhalation of respiratory droplets. (1, 2, 3 and 4)

While the previous studies were not specific to SARS-CoV-2, we do also now have direct evidence that shows masks are also an important mitigation measure for this virus. (This data is reviewed comprehensively here.) CDC mask recommendations reflect his body of evidence.

  • Studies comparing countries or regions that did have masking with those that did not mask demonstrate reduction in transmission and/or lower mortality when masks were worn.
  • Studies that model airborne exposure, including this one, demonstrate that face masks lower the chance of transmission of SARS-CoV-2, especially when everyone is wearing a mask to keep viral levels low and when masks are combined with other layers of protection.
  • Epidemiological studies have also repeatedly demonstrated reduced transmission with mask wearing. These studies include:
  1. The case of infected hairdressers not transmitting to their clients when all were masked.
  2. Case studies from the U.S Naval ship and China showed show that those who wear masks are less likely to catch SARS-Cov-2 from infected household members.
  3. A study from Thailand that shows wearing a mask at all times in public was associated with a lower risk of infection compared to not wearing a mask.  

Masks are an important, safe, inexpensive, and powerful tool to help control the spread of COVID, especially when most people wear them. Until we have higher vaccine coverage, continued use of masks in combination with other mitigation strategies will be necessary.

These precautions are meant to be practiced together. Each is like a slice of Swiss cheese. Alone, each precaution is imperfect, but when we layer them, we close more holes.  Layers of protection, including masks, remain our key to controlling this pandemic. 

Are masks safe?

In addition to wondering if masks really work, you might be wondering if masks are safe for you and your kids. The answer to that question is yes! The American Lung Association supports masking and its safety for kids over two years of age, as does the American Academy of Pediatrics

Scientific studies show that masks are not detrimental, including this one that showed no detrimental effects of wearing a surgical mask in healthy people or those with chronic obstructive pulmonary disease. A highly publicized study that has been shared as evidence of harm from masking has been retracted by JAMA Pediatrics after major methodological flaws were identified. In addition, more informative than any single study, we have extensive real-life evidence that masks are safe. Kids and adults with certain health conditions regularly mask without adverse effects. We also have the experience of millions of people and millions of children who have been successfully and safely wearing masks for the past year and a half. If masks were harmful, we would see adverse health events reported worldwide, but we do not.

Another common concern is that wearing masks will impair the development of children, particularly for learning to infer emotions from people around them. However, studies like this study show that children can still accurately infer emotion from people masking. We also must consider the effects of the alternative (not masking) on children’s development. Not masking jeopardizes children being in school and interacting with friends and family, which are clearly important for kids’ development. Masking allows this all to happen, while also minimizing health risks. 

In addition, most school districts provide accommodations for children who cannot wear masks (like those with hearing loss or speech delay), and this underscores why it is so important for everyone else who is able to protect them by masking, vaccinating, and adhering to other guidelines. There are also accommodations, like clear masks or sensory-friendly masks, that can help protect kids in these situations.

Given the severity of the COVID-19 pandemic, it is critical to do what we can to help slow the spread of SARS-CoV-2. Wearing a mask is a safe and effective way to help do this.

CDC mask recommendations will likely change as we learn more

Even though the COVID-19 pandemic has been with us for many months there are a lot of things we are still learning about this virus and the pandemic is continually changing. This means recommendations about masks and other precautions will continue to change as evidence is updated and the virus continues to spread.  The United States is not alone in requiring masks to slow the spread of SARS-CoV-2. Other countries, professional organizations, and our current understanding of the virus supports this policy. The delta variant has changed the dynamics of the pandemic. We have accumulated scientific knowledge and direct evidence that masks really do work to slow the spread. So, if you retired your mask, please pull it back out. We are in a better position than we were last year, but the pandemic isn’t over yet.


Our recommended posts about new mask guidelines:


Liz’s Instagram post about the new mask guidance

Do masks still protect kids if no one else is masking? — Dear Pandemic

Advocating for kids: Resources that can help – Your Local Epidemiologist

SciMoms COVID FAQ: Masks

SciMoms COVID FAQ: SARS-CoV2 spread

SciMoms COVID FAQ: Immunity and Herd Immunity

Elisabeth Marnik PhD (she, her, hers) is a scientist, mom, and an Assistant Professor of Molecular Biochemistry & Microbiology. She completed her PhD at Tufts University where she used genetic tools to understand the role of specific CD4+ T cells in our immune system. Liz is passionate about making science understandable and accessible to everyone, so in her spare time she communicates science on social media. You can find her on Instagram or Facebook. When she’s not doing science she enjoys spending time with her family and is an avid runner.