Masks appears to do more than protect others during COVID-19. They protect the mask user, too.
That’s the finding of a report written by infectious disease experts that’ll publish soon in the Journal of Internal Medicine.
GV Wire℠ received an advance copy of the report from Dr. Monica Gandhi, one of the study’s co-authors. Gandhi is a professor of medicine at UC San Francisco and associate division chief of the infectious diseases program at San Francisco General Hospital.
Lower Dose of Virus if Wearing Mask
“Masks work,” Ghandi said in an email. “They protect others but they also protect you. You will get in a lower dose of virus if you wear a mask and are exposed to COVID-19 and are very likely to have mild or no symptoms.”
“You will get in a lower dose of virus if you wear a mask and are exposed to COVID-19 and are very likely to have mild or no symptoms.”–Dr. Monica Gandhi, UC San Francisco
Depending on how robust the person’s immune system is, a smaller exposure appears to correlate with milder cases of COVID-19. It’s probably because with a smaller amount of virus to deal with, the body’s immune system has a better chance of mounting a defense, the paper’s authors suggest.
It also appears people who wear masks but contract the disease are much more likely to be asymptomatic, meaning they have COVID-19 but no symptoms.
Theory of Viral Inoculum
Researchers focused on the theory that mask wearers receive less airborne COVID-19 droplets, and therefore give their immune systems a better chance of fighting off the droplets that get through. It’s what the writers call the theory of viral inoculum.
The theory that exposure to a lower dose of any virus (whether respiratory, gastrointestinal, or sexually-transmitted) can make subsequent illness far less likely to be severe has been discussed for some time.
The researchers’ goal was to deliver one of the first perspectives discussing evidence to support this theory.
Read the Study
Hamsters, Cruise Ships & Food Processing Plant Examples
Studying this theory on humans is not possible because exposing humans to varying levels of COVID-19 is not ethical.
But, a frequently-cited study shows that hamsters are less likely to contract SARS-CoV-2 infection with a surgical mask partition. Those hamsters that did contract COVID-19 with simulated masking had milder manifestations of infection, Ghandi’s report says.
One of the earliest estimates of asymptomatic COVID infection was from the COVID-19 outbreak on the Diamond Princess cruise ship. Masks were not provided on the ship and the number of asymptomatic infections was below 20%, the report states.
In a more recent report from a different cruise ship outbreak aboard the Ernest Shackleton, all passengers were issued surgical masks and all staff provided N95 masks after the initial case of COVID-19 on the ship was detected. In that setting with masking, where 128 of 217 passengers and staff eventually tested positive for COVID-19, the study states that 81% of infected patients remained asymptomatic, compared to 18% on the Diamond Princess.
The authors also referenced a recent outbreak in a seafood processing plant in Oregon where all workers were issued masks each day at work. The rate of asymptomatic infection among the 124 infected was 95%.
Faster Immunity & Slower Spread
The authors write, “Exposing society to SARS-CoV-2 without the unacceptable consequences of severe illness with public masking could lead to greater community-level immunity and slower spread as we await a vaccine.”
Says Dr. Gandhi: “We can get through this pandemic much more quickly – in the next 6 weeks, estimates say — if we all wear a mask. So do it as this pandemic is miserable!”