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As SARS-CoV-2 continues its global spread, it is possible that one of the mainstays of controlling the Covid-19 pandemic, universal facial masking, could help reduce the severity of the disease and ensure that greater proportion of new infections are asymptomatic. If this hypothesis is confirmed, universal masking could become a form of “variolation” that would generate immunity and thus slow the spread of the virus in the United States and elsewhere, while we wait for a vaccine.
A major reason for population-wide facial masking became apparent in March, when reports began circulating describing the high rates of SARS-CoV-2 viral shedding from the nose and mouth of patients who were presymptomatic or asymptomatic. : spread rates equivalent to those of symptomatic patients.one Universal facial masking appeared to be a possible way to prevent transmission from asymptomatic infected people. Therefore, the Centers for Disease Control and Prevention (CDC) recommended on April 3 that the public wear cloth face coverings in areas with high community transmission rates, a recommendation that has been unevenly followed in the United States. U.S.
Past evidence related to other respiratory viruses indicates that facial masking can also protect the user from infection by blocking the entry of viral particles into the nose and mouth.two Epidemiological investigations conducted around the world, especially in Asian countries that became accustomed to masking the entire population during the 2003 SARS pandemic, have suggested that there is a strong relationship between public masking and pandemic control. Recent data from Boston shows that SARS-CoV-2 infections decreased among healthcare workers after universal masking was implemented in municipal hospitals in late March.
SARS-CoV-2 has the protein capacity to cause innumerable clinical manifestations, ranging from a total absence of symptoms to pneumonia, acute respiratory distress syndrome and death. Recent virological, epidemiological, and ecological data have led to the hypothesis that facial masking may also reduce the severity of the disease among people who become infected.3 This possibility is consistent with a long-standing theory of viral pathogenesis, which holds that the severity of the disease is proportional to the viral inoculum received. Since 1938, researchers have explored, primarily in animal models, the concept of the lethal dose of a virus, or the dose at which 50% of exposed hosts die (LD50). In viral infections in which host immune responses play a predominant role in viral pathogenesis, such as SARS-CoV-2, high doses of viral inoculum can overwhelm and deregulate innate immune defenses, increasing disease severity. . In fact, downregulation immunopathology is one mechanism by which dexamethasone improves outcomes in severe Covid-19 infection. As proof of concept that viral inoculums influence disease manifestations, higher doses of administered virus led to more severe manifestations of Covid-19 in a Syrian hamster model of SARS-CoV-2 infection.4
If viral inoculum is important in determining the severity of SARS-CoV-2 infection, an additional hypothetical reason to use face masks would be to reduce the viral inoculum the wearer is exposed to and the subsequent clinical impact of the disease. Since masks can filter some virus-containing droplets (with the filtering capacity determined by the type of mask),two masking could reduce the inoculum that an exposed person inhales. If this theory is corroborated, population masking, with any type of mask that increases acceptability and adherence,two could contribute to increasing the proportion of SARS-CoV-2 infections that are asymptomatic. The CDC estimated that the typical rate of asymptomatic infection with SARS-CoV-2 was 40% in mid-July, but asymptomatic infection rates are reported to be greater than 80% in settings with universal facial masking, providing evidence observational of this hypothesis. Countries that have adapted entire population masking have performed better in terms of rates of severe Covid-related illness and death, which, in settings with limited evidence, suggests a shift from symptomatic to asymptomatic infections. Another experiment in the Syrian hamster model simulated surgical masking of animals and showed that with simulated masking, hamsters were less likely to become infected and, if infected, were asymptomatic or had milder symptoms than unmasked hamsters.
The most obvious way to prevent society from suffering the devastating effects of Covid-19 is to promote measures to reduce both the transmission and the severity of the disease. But SARS-CoV-2 is highly transmissible, it cannot be contained with syndromic-based surveillance alone,one and it is proving difficult to eradicate, even in regions that implemented strict initial control measures. Efforts to increase testing and containment in the United States have been ongoing and have met with variable success, due in part to the recent surge in demand for testing.
Vaccine hopes are not just about infection prevention: most vaccine trials include a secondary outcome of decreasing disease severity, increasing the proportion of cases where the disease is mild or asymptomatic it would be a public health victory. Universal masking appears to reduce the rate of new infections; We hypothesized that reducing viral inoculum would also increase the proportion of infected people who remain asymptomatic.3
In an outbreak on a closed Argentine cruise ship, for example, where passengers were given surgical masks and staff were given N95 masks, the asymptomatic infection rate was 81% (compared to 20% in previous outbreaks of cruises without universal masking) . In two recent outbreaks at US food processing plants, where all workers received masks every day and were asked to wear them, the proportion of asymptomatic infections among the more than 500 people who became infected was 95% , with only 5% in each case. outbreak experiencing mild to moderate symptoms.3 Case fatality rates in countries with compulsory or forced masking of the entire population have remained low, even with case resurgence after the closures were lifted.
Variolation was a process by which people susceptible to smallpox were inoculated with material extracted from the gallbladder of a person with smallpox, with the intention of causing a mild infection and subsequent immunity. Variolation was practiced only until the introduction of the variola vaccine, which eventually eradicated smallpox. Despite concerns regarding safety, global distribution, and eventual acceptance, the world has high hopes for a highly effective SARS-CoV-2 vaccine, and as of early September, 34 candidate vaccines were under clinical evaluation. and hundreds more in development.
However, while we await the results of vaccine trials, any public health measure that can increase the proportion of asymptomatic SARS-CoV-2 infections can make the infection less deadly and increase the immunity of the entire disease-free population. serious or fatalities. SARS-CoV-2 reinfection appears to be rare, despite more than 8 months of worldwide circulation and as suggested by a macaque model. The scientific community has been clarifying for some time the humoral and cell-mediated components of the adaptive immune response to SARS-CoV-2 and the insufficiency of antibody-based seroprevalence studies to estimate the level of T cells and memory B more durable. cellular immunity to SARS-CoV-2. Promising data have emerged in recent weeks suggesting that strong cell-mediated immunity results from mild or asymptomatic SARS-CoV-2 infection.5 so any public health strategy that can reduce the severity of the disease should also increase the immunity of the entire population.
To test our hypothesis that population-wide masking is one of those strategies, we need further studies comparing the rate of asymptomatic infection in areas with and without universal masking. To test the variolation hypothesis, we will need further studies comparing the strength and durability of SARS-CoV-2-specific T-cell immunity between people with asymptomatic infection and those with symptomatic infection, as well as a demonstration of the natural slowdown of SARS-CoV-2 spreads in areas with a high proportion of asymptomatic infections.
Ultimately, fighting the pandemic will mean reducing both transmission rates and the severity of the disease. Mounting evidence suggests that population-wide facial masking could benefit both components of the response.
