COVID-19 - 40% of Cases Asymptomatic May Point to Pre-existing Partial Immunity and Mask-related Lower Infecting Dose

An article in the Washington Post discusses the level of asymptomatic people within the population and the role of partial immunity and potential impact of infecting dose. Clearly here has been uneven transmission, especially with far less children being infected, but when we look at those who test positive, there are a high percentage who are asymptomatic, a number which CDC estimates to be about 40%. One thought is that these people have partial immunity, perhaps acquired from a past infection from the normal cold virus, or from some childhood vaccination. In fact, in samples of blood from people who had not had the disease, there was some immune reactivity to the virus by T-cells. .

Another interesting factor may be the impact of masks on how much virus a person encounters during an infection event. We had discussed infecting dose a few weeks back and now it does seem that this plays a factor. The evidence they provide is when looking at outbreaks among large groups where mask wearing was and was not used. In cases where the level of masking was high, the levels of asymptomatic infection was higher.

Washington Post - Health
https://www.washingtonpost.com/health/2020/08/08/asymptomatic-coronavirus-covid/
Forty percent of people with coronavirus infections have no symptoms. Might they be the key to ending the pandemic?
New research suggests that some of us may be partially protected due to past encounters with common cold coronaviruses.

By 

Ariana Eunjung Cha

August 8, 2020 at 1:31 p.m. EDT

When researcher Monica Gandhi began digging deeper into outbreaks of the novel coronavirus, she was struck by the extraordinarily high number of infected people who had no symptoms.

A Boston homeless shelter had 147 infected residents, but 88 percent had no symptoms even though they shared their living space. A Tyson Foods poultry plant in Springdale, Ark., had 481 infections, and 95 percent were asymptomatic. Prisons in Arkansas, North Carolina, Ohio and Virginia counted 3,277 infected people, but 96 percent were asymptomatic.

During its seven-month global rampage, the coronavirus has claimed more than 700,000 lives. But Gandhi began to think the bigger mystery might be why it has left so many more practically unscathed.

What was it about these asymptomatic people, who lived or worked so closely to others who fell severely ill, she wondered, that protected them? Did the “dose” of their viral exposure make a difference? Was it genetics? Or might some people already have partial resistance to the virus, contrary to our initial understanding?

Rest of article - https://www.washingtonpost.com/health/2020/08/08/asymptomatic-coronavirus-covid/