How often do we have to get COVID to stop getting COVID?

In October 2020, a few weeks before the experimental trial results for the BioNTech-Pfizer, Moderna and Oxford/AstraZeneca COVID-19 vaccines were released, German virologist Christian Drosten cautioned that the shots would be of limited effectiveness in preventing the spread of the disease.

"We are dealing here with an infection of the mucous membrane, i.e., in the nose and the throat and then later the lungs,” he said on Episode 62 of Das Coronavirus-Update, the podcast launched by broadcaster NDR in March 2020 that helped make Drosten a household name in Germany. "The mucous membranes already have their own special local immune system. With the current vaccines, which are more likely to be injected into the muscle, you don’t reach this local immune system so well.” As a result, the vaccines "probably protect more against the severe course (of the disease) than against infection.”

Which is of course exactly how things played out. The vaccines have been spectacularly effective at preventing severe disease and death, much less so at preventing transmission.