New theory: masks may provide immunity unnoticed

Man wears mouth and nose protection on the train.

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Whether on the train, on the bus or in business: mouth and nose protection is currently an indispensable part of everyday life for Germans. Masks have been shown to protect against coronavirus infections by shielding a large portion of the viral load expelled when speaking, coughing, or sneezing.

However, masks do not protect one hundred percent. Small droplets laden with the virus can penetrate outside with the air despite mouth and nose protection. According to a new scientific theory recently presented in the New England Journal of Medicine, this initially threatening-sounding scenario could have a decisive advantage.

Mild course, strong immune reaction

The researchers suspect that the small amount of pathogens ingested by the counterpart could only lead to a mild or asymptomatic infection, but the body’s immune response is strong enough to develop immunity against the virus. Masks could thus enable a kind of live vaccine, according to the theory of Monica Ghandi and George Rutherford of the University of California at San Francisco.

“In principle, the article is very interesting and plausible in many points,” said Melanie Brinkmann from the Helmholtz Center for Infection Research at the “Science Media Center”. “But I am a bit skeptical because it is based on two assumptions that have not yet been scientifically proven for SARS-CoV-2: First, that a lower dose of the virus causes less severe symptoms or illness and, second, that mild or asymptomatic infections are one trigger long-lasting immune protection, ”continues Brinkmann.

The theory that a small amount of a pathogen leads to a mild course and nevertheless to a strong immune reaction is not entirely new.

Before the invention of the smallpox vaccine, the first vaccine in medical history, so-called variolation was common. Doctors applied a small amount of pustular secretions from people with smallpox to the skin of healthy people. This should lead to a mild illness and immunity in the previously healthy person.

However, since this treatment had hardly foreseeable effects and also led to severe or even fatal courses of the disease, it was abolished with the introduction of the vaccine.

Many questions remain open

How the amount of viral load of the novel coronavirus will affect the course of the disease in people is still uncertain. According to Brinkmann, a “dose-response effect” is only known from studies with animals. A study on hamsters showed that the animals became ill to different degrees depending on the amount of viruses to which they were exposed. A similar study with humans is difficult to conduct for ethical reasons.

And there are still a lot of uncertainties about the immune response. Although immune responses have also been demonstrated in people with mild disease courses, it is still uncertain how long protection will last.

The researchers’ thesis is therefore initially being put to the test. You yourself write in the article: “To test our hypothesis, we need further studies that compare the proportion of asymptomatically infected people in areas with and without everyday masks.”


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