How contagious is COVID-19?
COVID-19 is very contagious, and a huge portion of the global population is vulnerable.
Scientists quantify the contagiousness of a disease with a figure called R0 - pronounced R-nought.
The figure refers to how many other people one sick person is likely to infect on average in a group that’s susceptible to the disease (meaning they don’t already have immunity from a vaccine or from fighting off the disease before)
An R0 of 2, for example, means each infected person is expected to spread the virus to two others, on average. COVID-19 is currently believed to have an R0 between 2 and 2.5.
The R0 is “a combination of the properties of the virus, and the way that humans interact.”
That makes it more contagious than the seasonal flu. With the flu, there are people in the population who have some level of immunity to it — either because of a vaccine or because they have been exposed to that strain of flu in the past. That’s not the case here.