We’ll Have Herd Immunity by April

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

In large part because natural immunity to previous infections is far more abundant than tests can measure. Tests have only detected 10-25% of infections, depending on when someone got the virus during the pandemic. Applying a time-weighted case capture average of 1 in 6.5 to the cumulative 28 million confirmed cases would mean that about 55% of Americans have natural immunity.

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

There is reason to believe that the country is headed for extremely low levels of infection. As more people became infected, most of whom had mild or no symptoms, fewer Americans needed to be infected. At this point in time, I expect Covid to be largely gone by April so Americans can live normally again.

Antibody studies almost certainly underestimate natural immunity. Antibody tests do not detect antigen-specific T cells, which develop a “memory” once activated by the virus. In 2008 – 90 years later – survivors of the Spanish flu of 1918 were found that memory cells can still produce neutralizing antibodies.

Researcher near Sweden Karolinska Institute found that the percentage of people who showed a T cell response after mild or asymptomatic Covid-19 infection consistently exceeded the percentage with detectable antibodies. T cell immunity was present even in people who were exposed to infected family members but never developed symptoms. A group of British scientists in September indicated that the medical community may underestimate the prevalence of immunity to activated T cells.

Covid-19 deaths in the US also suggest much broader immunity than recognized. Approximately 1 in 600 Americans have died from Covid-19, which translates into a population death rate of approximately 0.15%. The death rate from Covid-19 infections is around 0.23%. These numbers show that roughly two-thirds of the US population had the infection.

In my own conversations with medical experts, I have found that too often they reject natural immunity, arguing that we have no data. The data certainly does not fit the classic model of the randomized, controlled study of the medical establishment of the old guard. There is no control group. However, the observational data are convincing.

I have argued for months that if those with previous Covid-19 infection stopped vaccines until all seniors at risk got their first dose, we could save more American lives. Several studies show that natural immunity should protect those who have had Covid-19 until more vaccines are available. Half of my friends in the medical community said to me, good idea. The other half said that there is insufficient data on natural immunity, although reinfections have re-emerged less than 1% of people– and when they do occur the cases are mild.

However, the consistent and rapid decline in daily cases since January 8th can only be explained by natural immunity. The behavior did not suddenly improve during the holidays. Americans traveled more over Christmas than they had since March. Nor do vaccines explain the sharp drop in January. Immunization rates have been low and take weeks to kick in.

My prediction that Covid-19 will be largely gone by April is based on laboratory data, math data, published literature, and discussions with experts. But it is also based on direct observation of how difficult it was to conduct tests, especially for the poor. If you live in a wealthy community where worried people are on the alert when it comes to getting tested, you may think that testing catches most infections. However, if you’ve seen the many barriers to testing on low-income Americans, you might think that very few infections have been recorded in testing centers. Keep in mind that most infections are asymptomatic, which still triggers natural immunity.

Many experts, as well as politicians and journalists, are afraid to talk about herd immunity. The term has political overtones because some have suggested that the US simply rip Covid up to achieve herd immunity. It was a ruthless idea. However, herd immunity is the inevitable result of the spread and vaccination of viruses. When the chain of virus transmission has been broken in multiple places, it becomes more difficult to spread – and that includes the new strains.

Herd immunity is well documented in the Brazilian city of Manaus Researchers in the Lancet reported a 76% prevalence of previous Covid-19 infection, which resulted in a significant slowdown in infection. Doctors observe a new load that threatens to escape the previous immunity. But also countries in which new variants have appeared, such as Great Britain, South Africa and Brazil, are recording significant decreases in new cases every day. The risk of new variants mutating around previously vaccinated or natural immunity should be a reminder that Covid-19 will persist for decades after the end of the pandemic. There should also be a sense of urgency to develop, approve and administer a vaccine that targets new variants.

Some medical experts privately agreed with my prediction that there may be very little Covid-19 by April, but suggested not to speak publicly about herd immunity as people could become complacent and fail to take precautionary measures or reject the vaccine . But scientists shouldn’t try to manipulate the public by hiding the truth. As we encourage everyone to get vaccinated, we also need to reopen schools and society to limit the damage from closings and prolonged isolation. Contingency planning for an open economy by April can give hope to the desperate and those who have made great personal sacrifices.

Dr. Makary is a professor at the Johns Hopkins School of Medicine and the Bloomberg School of Public Health, chief medical officer of Sesame Care, and author of The Price We Pay.

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