Universal mask wearing decreases the chance of infection and, if infected, decreases the amount of virus particles (inoculum) a mask-wearer is exposed to thus causing only asymptomatic infection or mild COVID-19 disease.
The idea of allowing people to get naturally infected with novel coronavirus in order to achieve herd immunity even before safe and effective vaccines become available has now been dismissed. Now, a few researchers are suggesting an alternative hypothesis. According to the hypothesis, universal mask wearing decreases the chance of infection and, if infected, decreases the amount of virus particles (inoculum) a mask-wearer is exposed to thus causing only asymptomatic infection or mild COVID-19 disease.
Dr Monica Gandhi and Dr Eric Goosby from the University of California, San Francisco and Dr Chris Beyrer from the Johns Hopkins Bloomberg School of Public Health , Baltimore, argue that exposure to the virus “without the unacceptable consequences of severe illness” through universal masking can lead to greater spread of immunity in the community thus eventually slowing down the spread of the virus even as the world awaits an effective vaccine.
Advantages to the mask wearer
Depending on the type and fit of masks common people use, the amount of virus particles a person is exposed to may be reduced even if infected. According to Dr Beyrer, cloth masks can screen out between 65% and 85% of viral particles.
While much attention has been on the role of masks in reducing or preventing the spread of viral from an infected person to others, the possibility of a healthy mask-wearer getting exposed to only smaller amount of virus and the possible effects of such exposure has not received equal attention, the researchers write in an article published in the Journal of General Internal Medicine. Dr Gandhi and Dr George W. Rutherford from the University of California, San Francisco advance the same idea in a recently published perspective piece in The New England Journal of Medicine.
A growing body of virologic, epidemiologic, and ecologic evidence suggest that universal masking can reduce the severity of disease among people who do become infected, they write. “We have known for more than 50 years that lower inoculums of other viruses, including flu, lead to milder illnesses. Since this is a basic principle in virology, it likely holds true for COVID-19,” Dr Beyrer told Johns Hopkins.
Virologic evidence
In a study on health participants exposed to wild-type influenza A virus, more severe symptoms were seen in those exposed to higher amounts of the virus.
A study involving hamsters helped understand the connection between novel coronavirus dose and disease severity. In the study, a surgical mask partition helped reduce the risk of infection in healthy hamsters that were separated from infected ones. And those healthy animals that did get infected had only milder manifestations of infection.
Epidemiological evidences
The best epidemiological evidence comes from Diamond Princess cruise ship and a ship in Argentina. While only 18% of passengers in the Diamond Princess cruise ship were asymptomatic, universal masking in the Argentina ship resulted in 81% (128 of 217 passengers and staff) of the infected remaining asymptomatic.
In a seafood processing plant in Oregon, U.S. universal masking could not completely prevent infection but among the 124 who were infected, 95% were asymptomatic. Similarly, in a Tyson chicken plant in Arkansas, masking resulted in 95% asymptomatic rate of infection.
Ecologic evidence comes from many Southeast Asian countries that had adopted universal masking from the beginning of the pandemic reporting fewer cases and deaths.
“If this theory bears out, population-wide masking, might contribute to increasing the proportion of SARS-CoV-2 infections that are asymptomatic,” they write in The New England Journal of Medicine. Since universal masking decreases viral inoculum leading to increase in asymptomatic infection that induces strong T cell immunity for some duration, “could masking be a crude vaccine until we get to a real vaccine?” Dr Gandhi asks in a tweet.
While a few studies have shown that immune responses are seen in asymptomatically infected individuals, the differences in the duration of protection between asymptomatic and symptomatic infection are not known yet.
No room for complacency
It is important that people do not misinterpret the hypothesis to think that one can intentionally inoculate oneself with the virus by wearing a mask. Since studies have not been conducted with the sole purpose of studying the effects of universal masking on COVID-19 severity through reduced virusinoculum, people who wear masks should not become complacent nor should people think that masks are useless as they cannot completely prevent infection in some individuals.
“I am not suggesting pox parties. Just saying masking could be good on multiple levels — decrease transmission, decrease disease severity, help drive up immunity,” Dr Gandhi tweeted.
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