In reducing the spread of the virus in the environment of infected people when they cough or speak, the port of the mask slows down the spread of the coronavirus Sars-CoV-2, responsible for the epidemic of Covid-19. Experiments in the laboratory, in the hospital and at the national level in some countries demonstrate that the masks are functioning effectively. Based on this evidence, the health authorities have, in many places, made wearing a mask standard. The Centers for disease control and disease prevention recommend, for example, to american citizens to cover their face (editor's NOTE : and the French authorities are doing the same, some municipalities have even made it mandatory to the outside).
I am a physician specialist in infectious diseases and professor of medicine at the university of California, San Francisco. When the port of the mask has begun to be recommended or made mandatory by the governments or on the workplace, my colleagues and I have noticed an interesting trend. In places where the majority of the people had complied with the port of the mask, the people infected by the Covid-19 appeared to be significantly less likely to develop a severe form of the disease compared with people working in places where the wearing of masks was less widespread. In other words, people seem to fall less sick if they are wearing a mask.
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The dose of virus during the infection determines the severity of the disease
When a respiratory virus enters our body, it immediately starts to divert the cells near which it happens to turn them into machines to produce viruses. To stop the spread of virus, the immune system sets in motion and tries to stop this process. The severity of the disease that you will develop it after a viral infection has a lot to do with the amount of virus (the inoculum viral ", or dose viral) to which you have been exposed·e initially. If the dose when the exposure is very high, the immune response may be exceeded. Between the fact that the virus takes hold of a large number of cells and considerable efforts deployed by the immune system to contain the infection, the body undergoes a lot of damage, which can lead to the result that the infected person gets very sick.
On the other hand, if the initial dose of virus is low, the immune system is able to contain the virus by using measures that are less drastic. In this case, the person shows less symptoms, if any. This concept of a link between dose viral and disease severity existed for nearly a century. Numerous studies on animals have shown that the higher the dose of virus administered to an animal is, the higher it is sick. In 2015, researchers have tested this concept in human volunteers using an influenza virus non-fatal. They have got the same result : the higher the dose of influenza virus administered to the volunteers was high, the more the disease was important.
last July, researchers published an article showing that the dose viral was related to the severity of the disease in the hamsters exposed to the coronavirus Sars-CoV-2. The hamsters that received a dose of viral higher fell more seriously ill than the hamsters that received a lower dose. On the basis of this research, therefore, it seems highly likely that, if you are exposed to Sars-CoV-2, the larger the dose will be low, the lower the risk that the symptoms of the disease are serious will be high. Then, how can we reduce the exposure dose ?
The masks reduce the dose viral
most researchers and epidemiologists specialized in infectious diseases believe that the coronavirus is spread mainly by droplets and, to a lesser extent, through aerosols. Research has shown that surgical masks or cloth can stop the majority of the particles that could contain the Sars-CoV-2. Of course, no mask is perfect. However, the goal is not to block 100 % of the virus, but reduce the amount of particles that you could inhale. Gold almost all masks do.
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The latest evidence that masks reduce the dose of virus was again obtained through experiments on hamsters. By placing surgical masks on the tubes that lead the air in their cages, the researchers created a group of rodents " hidden ". Another group of hamsters, which the air hoses were without masks, was witness to " not hidden ".
hamsters infected with the coronavirus have been placed in cages next to the hamsters masked and non-masked, and the air has been pumped from the cages of the "infected" to the cages of the hamsters not infected, masked and non-masked. As expected, the hamsters "hidden" proved to be less likely to be infected by the Covid-19. What's more, those hamsters hidden who have been infected have developed a more benign disease than their counterparts who were not masked.
The port of the mask increases the rate of asymptomatic cases
In July, the CDC estimated that approximately 40 % of persons infected with the Sars-CoV-2 are asymptomatic. A figure confirmed by a number of other studies. However, in places where everyone wears a mask, the rate of asymptomatic infections seems to be much higher. At the end of march, an outbreak of Covid-19 expressed on a cruise ship australian, Greg Mortimer. After the first case of Covid-19 has been identified, the passengers were all given surgical masks and staff had N95 masks (editor's NOTE : masks filter at least 95% of particles of diameter less than 2.5 µm. The european equivalent is FFP2, which the filtration rate is 94 %). The use of masks was very well respected. Result : even if 128 of the 217 passengers and members of the staff have the final tested positive for the coronavirus, 81 % of infected persons remained asymptomatic.
Both outbreaks over recent years have also brought other evidence. The first is stated in a factory for seafood processing in Oregon and the second in a factory chicken processing in Arkansas. In these two places, the workers were provided with masks and were required to wear them at all times. Nearly 95 % of infected people working in these two factories have proved to be asymptomatic.
There is no doubt that wearing a mask generalized slows down the spread of the coronavirus. For my colleagues and myself, a converging beam of indices shows that the masks also protect the wearer, whether the results of the experiments conducted in the laboratory, case studies such as those on epidemic outbreaks are reported on cruise ships and in food processing plants, or of certain biological principles known for a long time. The tools put in place to combat this pandemic have two objectives : to slow the spread of the coronavirus and save lives. The generalization of a mask allows you to achieve both.
*Monica Gandhi is a professor of medicine in the department of HIV, Infectious Diseases and Global Medicine, university of California, San Francisco.p>
Consult our folder : Covid-19 : the spectrum of the second wave