In epidemiology, we determine "heard immunity" by calculating the proportion of the population that is in the Recovered (R) compartment (either through natural

In epidemiology, we determine "heard immunity" by calculating the proportion of the population that is in the Recovered (R) compartment (either through natural or artificial means). If your proportion that is in R is greater than 1-(1/R0) the incidence of the disease will start to decline. Thankfully the R0 of SARS-COV-2 seem to be around 1.4–2.5 (meaning you need ~30% to ~60% recovered), so a vaccine would be actually very effective. I highly suspect "Travel to Europe" (i.e. international travel) may still be delayed for a long bit until we've gotten around to ~50-60% immunized, but it's tough to say. https://academic.oup.com/cid/article/52/7/911/299077 https://academic.oup.com/cid/article/52/7/911/299077 https://en.wikipedia.org/wiki/Compartmental_models_in_epidemiology https://en.wikipedia.org/wiki/Compartmental_models_in_epidem...