What we do and do not know about COVID-19’s infectivity and viral load

As the COVID-19 pandemic spreads, it has become clear that people need to understand basic facts about SARS-CoV-2, the virus that causes COVID-19, to make informed health care and public policy decisions. Two basic virological concepts have gotten a lot of attention recently – the “infectious dose” and the “viral load” of SARS-CoV-2.

As influenza virologists, these are concepts that we often think about when studying respiratory virus infections and transmission.

What is an ‘infectious dose’?

The infectious dose is the amount of virus needed to establish an infection. Depending on the virus, people need to be exposed to as little as 10 virus particles – for example, for influenza viruses – or as many as thousands for other human viruses to get infected. Continue reading.