Johns Hopkins professor predicts U.S. will achieve collective immunity by April, but many experts aren’t so optimistic

• In a Wall Street Journal editorial, Professor Martin Makary of Johns Hopkins wrote that COVID-19 would be “mostly gone” to the United States in April.

• The decline in coronavirus cases in the United States suggests that it is close to achieving collective immunity, Makary said.

• But many doctors and scientists say herd immunity is still a long way off in the United States.

• Visit Insider’s Business section for more stories.

Related: What Coronavirus Stress Does To Your Brain & Body

Daily cases of coronavirus in the United States fell 65% last month – a record drop during the outbreak in the country. New cases hit an all-time high of 312,000 on January 8. Since then, they have fallen to a weekly average of around 73,000 per 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 could be on the verge of achieving collective immunity. .

In an editorial Thursday, Makary predicted that COVID-19 would be “almost gone” in April.

He wrote that the infections were likely much more widespread than the data suggests – so much so, in fact, that the United States will soon reach a threshold beyond which the virus will not be able to easily pass from person to person. the other.

“The steady and rapid decline in daily cases since January 8 can only be explained by natural immunity,” Makary wrote. “Behavior didn’t suddenly improve over the holidays; Americans traveled more on Christmas than they had since March.”

He added that vaccines “do not explain the sharp drop” since early January, as “vaccination rates were low and they take weeks to take effect.”

But many other doctors and public health experts continue to warn that herd immunity is still a long way off in the United States – especially as more contagious variants spread.

“We’re nowhere near community immunity or population immunity or whatever people want to call it at this point,” said Dr. Cindy Prins, an epidemiologist at the University of Florida, to Insider. “We’re still a long way from that.”

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Could 55% of Americans already have natural immunity?

Researchers generally estimate that the reproductive value of the coronavirus – at least that of the original strain – is between 2 and 3 in the absence of vaccines or public health measures. This means that to achieve herd immunity, about 50% to 67% of a population would need some immunity against the virus – whether through vaccination or through natural infection.

“In theory, the numbers are around 70% – some say 65%, some say 75%, 80% – but it’s usually around those numbers. So it takes a while before you can get there,” Dr. Eyal Zimlichman, deputy general manager of Sheba Medical Center, Israel’s largest hospital, told Insider in January.

But Makary’s editorial suggested that “observational data” indicates the United States is near the threshold for herd immunity.

Assuming the tests only capture 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 writes, “and the number is rising rapidly.”

Makary did not respond to Insider’s request for comment on this story.

Other factors could explain the drop in American 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 lockdown, which began in December, may have partially contributed to the decline. At the height of its epidemic, California accounted for about 40,000 daily cases of coronavirus in the United States, on average.

Other factors like mask wear, social distancing and less travel after the holidays likely also played a role.

“If I ranked the explanations for the drop 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 the week after Thanksgiving and Christmas, activity has gone down.”

Thompson also pointed out that some communities may have a greater share of immunity than others.

“Immunity is probably concentrated among people who have been unlikely to avoid the disease, such as the homeless, frontline and essential workers, and people living in overcrowded multigenerational homes,” he said. -he writes. “It could also include people who were more likely to contract the virus because of their lifestyle and values, such as risk-tolerant Americans who ate at indoor restaurants.”

Even though the United States is far from immune to herds, it is possible that high levels of immunity in people with frequent social interactions could help slow transmission.

But there is no concrete data yet to suggest that the majority of Americans are immune to the coronavirus.

The Centers for Disease Control and Prevention estimates that a quarter of the American 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 was infected by April. A more recent study found that as of mid-November, about 14% of the American population had antibodies to the coronavirus.

“Even after adjusting for underreporting, a substantial gap remains between the estimated proportion of the infected population and the proportion infected necessary to achieve herd immunity,” the authors wrote.

Variants make collective immunity a moving target

Zimlichman said the very idea that a nation can achieve collective immunity with the coronavirus has “never been tested.” This is because the required threshold is often a moving target – and it can increase as new, more contagious variants spread.

Studies have shown that the most contagious variant of coronavirus found in the UK, called B.1.1.7, can increase the reproductive value of the virus by 0.4 to 0.9. In this case, up to 75% of the American population would likely need to develop some form of immunity.

“When you have a new variant of COVID, if the reproduction number is higher, it means that the virus is going to be able to spread even if fewer people are susceptible,” said Rahul Subramanian, a data scientist at the University recently. from Chicago. Insider said.

With that in mind, he said, “I would hesitate to say that we have achieved collective immunity.”

Achieving collective immunity could be even more difficult if vaccines prove to be less effective against the newer variants or if people refuse to be vaccinated.

Some research suggests that vaccines may not work as well against the more infectious variant found in South Africa. And 13% of adults in the United States say they won’t get a coronavirus vaccine, according to a recent Kaiser Family Foundation survey.

“Obviously you will have problems with people who refuse to get vaccinated for whatever reason,” Zimlichman said, “so getting herd immunity through vaccination is hard to come by.”

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