The “dose” of coronavirus a person gets may determine how sick they get

The “dose” of coronavirus you are exposed to might make a difference as to whether you become asymptomatic, mildly sick or critically ill.

It's not because you need a certain number of particles of virus to infect a cell; it just increases the odds that one of those viral particles will make it into the cell and infect it, setting off the chain reaction.

There's another dimension to viral dose, and it has to do with time. It’s not the dose of the virus you get at one point in time that matters; it may also be the sum of viral doses you get over a certain period of time.

 

In mid-October, the US Centers for Disease Control and Prevention changed its definition of "close contact" to include multiple, brief exposures that add up to 15 minutes or more with an infected person. Previously, the CDC defined a close contact as 15 minutes of continuous exposure to an infected individual.

Then there is the concept of viral load. Viral load is the amount of virus an infected person has in their body. Some, but not all, studies have shown that the sicker a patient is with Covid-19, the higher the viral load.

"If you get less of a viral dose in, then you can calmly take care of it and wall it off. You have this asymptomatic infection, and maybe you are less likely to produce a high viral load. You produce a lower viral load, and thus it's related to less severe disease," says Dr. Monica Gandhi, an infectious disease doctor and professor of medicine at the University of California, San Francisco.

This could help explain why some people never develop symptoms of Covid-19, but still have antibodies to the virus. But more research will need to be done to confirm that.