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In an opinion piece in the Wall Street Journal, Johns Hopkins professor Martin Makary wrote that COVID-19 would be “virtually extinct” in the United States in April.
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The drop in coronavirus cases in the U.S. suggests it is close to achieving collective immunity, said Makary.
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But many doctors and scientists say that collective immunity is still a long way off in the United States.
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Daily coronavirus cases in the United States fell 65% last month – a record drop during the outbreak in the country. The new cases reached a record high of 312,000 on 8 January. Since then, they have dropped to a weekly average of around 73,000 a day.
Dr. Martin Makary, professor of surgery at the Johns Hopkins School of Medicine, suggested in The Wall Street Journal that the most likely explanation for the decline is that the United States may be close to achieving collective immunity.
In an opinion piece on Thursday, Makary predicted that COVID-19 would be “practically dead” in April.
He wrote that infections have probably been far more widespread than the data suggest – so much, in fact, that the United States will soon reach a limit beyond which the virus will not be able to pass easily from person to person.
“The consistent and rapid decline in daily cases since 8 January can be explained only by natural immunity,” wrote Makary. “The behavior didn’t suddenly improve during the holidays; Americans traveled more at Christmas than they did since March.”
He added that vaccines “do not explain the sharp decline” since early January, because “vaccination rates were low and it took weeks to take effect”.
But many other doctors and public health experts continue to warn that collective immunity is still a long way off in the United States – particularly as more contagious variants spread.
“We are nowhere near the immunity of the community or the population or what people want to call it right now,” Dr. Cindy Prins, an epidemiologist at the University of Florida, told Insider. “We are nowhere near that yet.”
Could 55% of Americans already have natural immunity?
Researchers generally estimate that the reproductive value of the coronavirus – that of the original strain, at least – is between 2 and 3, in the absence of vaccines or public health measures. This means that in order to obtain herd immunity, about 50% to 67% of the population would need to have some immunity to the virus – either through vaccination or natural infection.
“In theory, the numbers are around 70% – some say 65%, some say 75%, 80% – but it is usually around those numbers. So it takes a while before you get there, ”Dr. Eyal Zimlichman, deputy general director of Sheba Medical Center, Israel’s largest hospital, told Insider in January.
But Makary’s article suggested that “observational data” indicates that the United States is close to the herd’s immunity limit.
Assuming the test captures only 10% to 25% of infections, he said, about 55% of Americans would already have natural immunity, based on the number of tests reported. Add to that 15% of Americans who have been vaccinated so far, he wrote, “and the number is increasing rapidly.”
Makary did not respond to Insider’s request to comment on this story.
Other factors may explain the drop in US cases
Experts say collective immunity is not the only possible explanation for the drop in the number of cases in the United States.
California’s second blockade, which began in December, may have partially contributed to the decline. At the peak of its outbreak, California accounted for about 40,000 of the daily coronavirus cases in the United States, on average.
Other factors, such as wearing a mask, social distance and decreased travel after holidays, probably also had their influence.
“If I were classifying the explanations for the decline in COVID-19, the behavior would be number one,” Ali Mokdad, professor of global health at the University of Washington, told The Atlantic. “If you look at the mobility data in the week after Thanksgiving and Christmas, activity has dropped.”
Thompson also pointed out that certain communities may have greater participation in immunity than others.
“Immunity is likely to be concentrated among people who have had few opportunities to prevent the disease, such as homeless people, frontline and essential workers and people living in crowded multigenerational homes,” he wrote. “It may also include people who are more likely to encounter the virus because of their lifestyle and values, such as risk-tolerant Americans who will eat in closed restaurants.”
Even if the United States is nowhere near collective immunity, it is possible that high levels of immunity among those with frequent social interactions may help delay transmission.
But there is still no hard data to suggest that most Americans are immune to the coronavirus.
The Centers for Disease Control and Prevention estimate that a quarter of the US population has been infected with the coronavirus so far. Even in New York City, where the virus spread widely in early 2020, studies found that 22% of the city’s population had been infected by April. A more recent study found that, in mid-November, about 14% of the US population had antibodies to the coronavirus.
“Even after adjusting for underreporting, there remains a substantial gap between the estimated proportion of the infected population and the proportion of infected people needed to achieve collective immunity,” wrote the authors.
Variants make herd immunity a moving target
Zimlichman said the very idea that a nation can achieve collective immunity with the coronavirus “has never been put to the test”. This is because the required threshold is often a moving target – and can increase as new, more contagious variants spread.
Studies have shown that the most contagious variant of the coronavirus discovered in the UK, called B.1.1.7, can increase the reproductive value of the virus by 0.4 to 0.9. In that case, up to 75% of the US population would likely need to develop some form of immunity.
“When you have a new variant of COVID, if the reproductive number is higher, it means that the virus will be able to spread even if fewer people are susceptible,” Rahul Subramanian, data scientist at the University of Chicago, recently said Insider.
With that in mind, he said, “I would hesitate to say that we have achieved collective immunity.”
Achieving collective immunity can be even more difficult if vaccines are less effective against new variants or if people refuse to get vaccines.
Some research suggests that vaccines may not work as well against the most infectious variant discovered in South Africa. And 13% of adults in the United States say they will not get the coronavirus vaccine, according to a recent survey by the Foundation. Kaiser family.
“Obviously, you will have problems with people who refuse to be vaccinated for any reason,” said Zimlichman, “so obtaining collective immunity from vaccination is difficult to achieve.”
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