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Opinion: I’m an epidemiologist. Here’s why San Diego Unified’s mask mandate won’t slow COVID-19. | #coronavirus | #kids. | #children | #schools


Ayers, Ph.D., M.A. is a Johns Hopkins- and Harvard-trained epidemiologist. He is the vice chief of innovation in the Division of Infectious Diseases and Global Public Health, associate professor in the Department of Medicine and affiliate scientist in the Qualcomm Institute, all at UC San Diego. He lives in San Diego. His summary of the evidence is his own and is not intended to reflect an official position of his employer.

The San Diego Unified School District adopted a mask mandate on July 18 for the last two weeks of summer school, automatically triggered by the prevalence of COVID-19 infections in the county. The intention of the policy, which could be reinstated for the new school year based on community spread, was to slow infection rates.

Such policies have been the subject of intense national media attention. Sadly, this is a reflection of how masking has become a divisive, political issue. However, San Diego Unified’s masking policy is ultimately about science and should be immutable to political fads.

Pre-pandemic, masking was discouraged by experts because the evidence then was negative on the protective effects of masking for the wearer. For instance, a randomized study of health care providers who wore cloth masks for four weeks in 14 hospitals in Hanoi, Vietnam, during 2011 found they experienced higher rates of respiratory illness, laboratory-confirmed viral infection and influenza-like illness than controls — who followed usual practice while working. Guidance by the World Health Organization in January 2020 stated that “cloth (e.g. cotton or gauze) masks are not recommended under any circumstance.”

With an abundance of uncertainty early during the pandemic, community masking using cloth or reusable surgical masks was encouraged in the hope that despite the lack of supporting real world evidence, there may be a community benefit if we all mask.

Observational studies that compared community practices supported this hope. However, this type of evidence is biased. Communities with higher masking rates are different from those with lower masking rates. For instance, communities with higher masking rates may have higher rates of working from home, social distancing and other protective practices. These differences, instead of masking, may be responsible for community infection rates.

Randomized controlled trials are the evidentiary gold standard. Treatments are assigned randomly to infer their “true effect” in the population. Trials are the basis of Food and Drug Administration full approvals and are intended to provide resolution for important scientific questions.

Misunderstandings about the quality of evidence have resulted in a substantial amount of misinformation and harm. When he was president, Donald Trump’s claims about the benefits of hydroxychloroquine and chloroquine were derived from observational studies and, as my colleagues and I showed, resulted in hundreds of thousands of people seeking and potentially using these medications. Later evidence from trials proved the use of these medications resulted in increased mortality. As a result, San Diego Unified’s policy should be informed by trials.

Fourteen of 16 trials performed before the pandemic found the recommendation to wear a mask did not significantly reduce infection rates compared to unmasked controls. Two trials on community masking have been performed during the pandemic. A trial in Denmark called DANMASK showed the recommendation to wear surgical masks did not reduce infections. A trial in Bangladesh showed reusable cloth masks did not reduce infections.

As designed, San Diego Unified’s masking policy, which includes reusable cloth masks and surgical masks, will likely not reduce the spread of COVID-19.

The larger environment in which the district’s mask policy is being implemented has also changed.

First, infection is about 80 percent less severe for the current variants compared to ancestral variants. Moreover, the risk of death from COVID-19 among children is less than 1/1,000th the risk to the elderly.

Second, the population through a combination of natural and vaccine-induced immunity is also more protected from severe disease. About 75 percent of kids had been previously infected with COVID-19 as of February.

What is the added protection from masking in this environment? If trials did not show a protective effect from community masking while the severity of illness was high and the public lacked any immunity, are masks a useful intervention now?

Similarly, the Centers for Disease Control and Prevention metrics used to trigger the district’s change in mask policy are outdated. These metrics, in part, use raw counts of hospitalized patients who are COVID-19 positive in the county.

Consider, NYU Langone Health reported about 65 percent of its COVID-19 patients were incidentally infected (e.g., the patient was admitted to give birth, because of an accident, elective procedure, etc., and tested positive). Using contemporary hospitalization rates in the same manner as one or two years earlier is comparing apples and oranges.

It is critical that the San Diego Unified school board be aware of the best evidence on masking, grade the quality of competing evidence and consider the underlying context in which policies are implemented.

Children’s compliance with the masking policy should not be a prerequisite to obtain in-person education, especially when the policy itself is not supported by robust evidence.

Editor’s note: A city schools spokesperson declined an offer for the district to contribute an essay on its mask mandate.





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