Now add people getting vaccinated. As of this week, 15% of Americans have received the vaccine, and the figure is rising fast. Former Food and Drug Commissioner Scott Gottlieb estimates 250 million doses will have been delivered to some 150 million people by the end of March.

There is reason to think the country is racing toward an extremely low level of infection. As more people have been infected, most of whom have mild or no symptoms, there are fewer Americans left to be infected. At the current trajectory, I expect Covid will be mostly gone by April, allowing Americans to resume normal life.

Antibody studies almost certainly underestimate natural immunity. Antibody testing doesn’t capture antigen-specific T-cells, which develop “memory” once they are activated by the virus. Survivors of the 1918 Spanish flu were found in 2008—90 years later—to have memory cells still able to produce neutralizing antibodies.