We’ll Have Herd Immunity by April

Covid cases have dropped 77% in six weeks. Experts should level with the public about the good news.

By Marty Makary. Excerpts:

"Amid the dire Covid warnings, one crucial fact has been largely ignored: Cases are down 77% over the past six weeks. If a medication slashed cases by 77%, we’d call it a miracle pill. Why is the number of cases plummeting much faster than experts predicted?

In large part because natural immunity from prior infection is far more common than can be measured by testing. Testing has been capturing only from 10% to 25% of infections, depending on when during the pandemic someone got the virus. Applying a time-weighted case capture average of 1 in 6.5 to the cumulative 28 million confirmed cases would mean about 55% of Americans have natural immunity.

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.

Researchers at Sweden’s Karolinska Institute found that the percentage of people mounting a T-cell response after mild or asymptomatic Covid-19 infection consistently exceeded the percentage with detectable antibodies. T-cell immunity was even present in people who were exposed to infected family members but never developed symptoms. A group of U.K. scientists in September pointed out that the medical community may be under-appreciating the prevalence of immunity from activated T-cells.

Covid-19 deaths in the U.S. would also suggest much broader immunity than recognized. About 1 in 600 Americans has died of Covid-19, which translates to a population fatality rate of about 0.15%. The Covid-19 infection fatality rate is about 0.23%. These numbers indicate that roughly two-thirds of the U.S. population has had the infection."

 "But the consistent and rapid decline in daily cases since Jan. 8 can be explained only by natural immunity. Behavior didn’t suddenly improve over the holidays; Americans traveled more over Christmas than they had since March. Vaccines also don’t explain the steep decline in January. Vaccination rates were low and they take weeks to kick in."

"Herd immunity has been well-documented in the Brazilian city of Manaus, where researchers in the Lancet reported the prevalence of prior Covid-19 infection to be 76%, resulting in a significant slowing of the infection. Doctors are watching a new strain that threatens to evade prior immunity. But countries where new variants have emerged, such as the U.K., South Africa and Brazil, are also seeing significant declines in daily new cases."