A: Although we ❤️ the part where it promotes mask-wearing, this intriguing idea has not been proven.
For now, keep wearing your mask (because it DOES reduce your likelihood of infecting others) and wait for the science to catch up with this hypothesis. It is not safe to put on a mask and purposely expose yourself to someone with COVID-19.
A recent commentary in the New England Journal of Medicine hypothesized that wearing a face mask may result in a lower “dose” of active virus, which decreases disease severity and maybe even provides immunity to COVID-19. This is a hypothesis–an idea yet to be tested.
The level of viral exposure does seem to have an effect on disease severity, but there is no known safe low dose of SARS-CoV-2–a dose that would be just enough to provoke an immune response but not enough to infect you.
Very likely, there is no one safe dose for everyone, because some people are more vulnerable than others.
Moreover, even if the safe dose was known, there’s no way to figure out the precise dose you might be getting with so many unknowns in the environment.
Finally, immune response from asymptomatic infections may not provide lasting immunity. So more questions than answers at this point.
The amount of virus needed to cause disease is called the minimum infectious dose. There is a link between viral exposure level and severity of disease for COVID-19. Higher levels of viral exposure are more likely to result in illness, and higher doses are related to more severe illness.
Due to examples of transmission from casual contact as well as pre-symptomatic transmission, researchers believe that the minimum infectious dose of SARS-CoV-2 is relatively low–likely in the range of hundreds of viral particles. The virus that caused the SARS outbreak in 2003 also had a low infectious dose.
A healthy person may have a mild illness from a low infectious dose. However, people with pre-existing conditions may have a serious illness even from a similarly low exposure. Individual risk factors such as age, immunocompromised status, hypertension, cardiovascular disease, and diabetes also play a role in disease severity for the same dose. That’s because people who have these risk factors may have an impaired immune system, resulting in more difficulty clearing the virus from their body. In addition, people with these risk factors may have increased viral entry receptor expression (ACE2 levels) or a predisposition to blood clots. Because each person’s body reacts differently to viral exposure, there is no low dose of virus considered “safe”.
The second part of the question is whether mild or asymptomatic illness can lead to protective immunity at all. There is also a link between disease severity and the immune response to SARS-CoV-2. Those with mild illness tend to have lower levels of antibody responses compared with patients who had a more severe disease course. Researchers have found that SARS-CoV-2-infected patients who were asymptomatic had lower levels of protective antibodies afterward, and they circulated for a shorter amount of time compared to patients who had symptoms. At this time, the minimum antibody levels that are sufficient to prevent infection with SARS-CoV-2 is unclear.
Vaccines have additional tricks that can boost immunity and make them even more effective than exposure to the live wild virus in terms of long-term protection from illness. Strategies like including immune-enhancing agents and boosters (multiple shots in series) can increase the immune response to provide long-term protection.
We will see from clinical trials whether vaccines can provide strong lasting immunity to the virus. Immune responses from populations wearing facemasks will also be monitored over time and provide further insight into immunity.
In short, there is no known “safe” exposure level and there is no guarantee that low viral exposure will lead to long-term protective immunity.
But, face masks are fantastic! They DO reduce the spread of the disease, protect you, and protect those around you –even if they do not result in long-term immunity for all wearers. Having a less severe infection or avoiding infection altogether is ideal from a personal level (no one wants to be critically ill) and from a public health point of view.