The double, even the triple effect of the mask? In addition to reducing the risk of catching COVID-19, it would reduce the severity of the disease in the event of infection and increase the immunity of the population, as a first step towards a vaccine, hope researchers.
“We believe that masks can be a kind of '' bridge '' towards a vaccine”, explains to AFP Prof. Monica Gandhi, specialist in infectious diseases at UCSF (University of California at San Francisco).
She set out her theory in a noted article published on September 8 by the prestigious American medical journal New England Journal of Medicine (NEJM).
This theory is based on a hypothesis: even if they catch COVID-19, a masked person is likely to develop a less severe form than if they had had their face uncovered, because they absorb a smaller amount of the virus (the ” inoculum ”).
“We are launching several studies to test this hypothesis, for example by looking at whether the requirement to wear a mask in certain cities around the world has reduced the severity of the disease there,” continues Professor Gandhi.
If the mask “increases the rates of asymptomatic infections” (without symptoms, editor's note), its generalized wearing would therefore theoretically “increase immunity” in the population and thus lead to “an intermediate control of the epidemic. while waiting for a vaccine, ”argues Professor Gandhi.
What “to give people an additional reason to wear the mask”, told AFP Professor George Rutherford, who co-authored the article with her.
The two researchers draw a parallel with “variolation”, a rudimentary technique used in the 18th century before the appearance of vaccines: it involved exposing a healthy person to a small quantity of smallpox virus, in the hope of immunize it.
The publication of the article in the NEJM had a strong echo.
“Of course, it remains a theory, but there are many arguments in its favor”, assures AFP Professor Bruno Hoen, director of medical research at the Institut Pasteur in Paris.
According to him, “we must take a different look at the use of the mask”, first deemed unnecessary by the health authorities, against a background of shortage, then advised to avoid contaminating others.
“It's an interesting theory based on a reasonable assumption,” adds Prof Archie Clements, an epidemiologist at Curtin University of Australia.
“I'm quite skeptical,” however tweeted Dr. Angela Rasmussen, virologist at New York University of Columbia. “It's an interesting idea, but there are too many unknowns.”
Its reservations: we are not sure that a lower dose of the virus results in a less severe form of COVID, we do not know how much the mask reduces this dose and the duration and the level of immunity are still poor known.
“Currently, there is no data proving that the mask attenuates the severity (of the disease) or that this would provide protection via variolation,” insisted Professor Rasmussen.
Hypothesis not verified
The problem is that the hypothesis of a link between the dose of virus and the severity of the disease cannot be verified other than by comparing existing situations, therefore with a lower level of proof than a study specifically set up for this. Indeed, from an ethical point of view, “we cannot deliberately expose humans to the virus”, underlines Professor Gandhi.
To develop her theory, however, she relied on several works.
Among other things, she cites a study carried out on hamsters by researchers in Hong Kong.
They simulated wearing a mask by placing it between cages containing on the one hand infected hamsters and on the other healthy hamsters. Verdict: Hamsters were less likely to catch COVID if they were “masked” and, even if they did catch it, their symptoms were milder.
Another argument is the comparison of the situation on different cruise ships affected by contamination.
On one of them, where the mask had been systematized, “the proportion of asymptomatic patients was 81%”, against “40%” in other vessels on which the mask was not generalized, argues Prof. Gandhi.
So many elements which show that this theory did not emerge “by chance”, according to Professor Hoen: “Monica Gandhi is the first to have made the synthesis, in a very elegant way, but the reflection had started before her”.
The person concerned recalls that the mask is not a panacea: “It must be accompanied by physical distancing, hand hygiene and other public health measures. We must not let our guard down and neglect them ”.