We will have herd immunity by April

Amid the dire Covid warnings, one crucial fact has been largely ignored: cases have fallen by 77% in the past six weeks. If a drug reduced cases by 77%, we would call it a miracle pill. Why is the number of cases dropping much faster than experts predicted?

In large part because natural immunity to a previous infection is much more common than what can be measured by tests. The tests captured only 10% to 25% of infections, depending on when during the pandemic someone contracted the virus. Applying a time-weighted case capture average of 1 in 6.5 to the 28 million cumulative confirmed cases would mean that about 55% of Americans have natural immunity.

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

There is reason to believe that the country is heading towards an extremely low level of infection. As more and more people have become infected, most of whom have mild symptoms or no symptoms, fewer Americans remain infected. On the current trajectory, I think Covid will be all but gone by April, allowing Americans to resume normal lives.

Antibody studies almost certainly underestimate natural immunity. Antibody tests do not 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 – with memory cells still capable of producing neutralizing antibodies.