Herd immunity to coronavirus may have been reached in New York, California, scientist claims

NEW YORK — While the wait for a coronavirus vaccine continues across the globe, one scientist believes that herd immunity to the virus is now a reality for some Americans. Data scientist Mark Last, a professor at Ben-Gurion University of the Negev in Israel, says that New York and California may have hit this potentially all-important mark.

He also suggests that Israel is quite close to reaching herd immunity as well, if it hasn’t already.

Herd immunity, or the idea that if enough people become infected with COVID-19 it will lead to immunity on a wide scale, is seen as a possible solution to the pandemic. Scientists and doctors rely on what’s known as the “reproduction number” or “R” to determine herd immunity. This refers to how many people an infected person is likely to transmit the virus to. When that number falls below one, herd immunity is achieved.

Herd immunity by the numbers

It’s believed that 60% of a population must have been infected to reach herd immunity. One recent study shows that number may actually be even lower at just 43%.

Professor Last is using what’s known as the SIR Model of Infection Dynamics for his analysis of the coronavirus. The model labels segments of the population as either “S” for susceptible, “I” for infectious, or “R” for recovered. He says that New York wasn’t far off from herd immunity in June when there was 400,000 confirmed cases. Antibody tests, however, suggested that there may have been six times that many infections (2.4 million).

If his numbers hold up, the state’s reproduction rate at the time would be 1.14. Since then, the state continues to report a consistent decrease in coronavirus cases. Last believes it may be enough of a drop for herd immunity. He calculates similar results for California as well as Israel.

“In California, it appears that herd immunity was reached around July 15 with slightly more than 10% of their population (4.05 million) being infected,” he says in a media release. “This means that their basic reproduction number R0 under current restrictions is only 1.1.

Coronavirus peak over in Israel?

“In Israel, a further lockdown is not necessary if the current restrictions are maintained and there are no unusual spreading events,” Last adds. “If we maintain the current restrictions, then my model predicts that we are at the end of this peak, which should tail off at the end of August or the beginning of September. Moreover, according to my calculations, we need 1.16 million people with antibodies in order to achieve herd immunity and we are very close to that number.”

It’s important to recognize, of course, that these findings are simply estimates from Last’s model. It’s impossible to know the true accuracy without actual test results.

“We cannot know the actual number of cases of infection unless we test the entire population every day. Initial serological tests conducted in Israel indicate the ratio of confirmed cases to actual cases is about 1:10. Using those numbers, we now have slightly above one million people with antibodies in Israel and we need at least 1.2 million,” he says.

Still, Last doesn’t want officials to ease up yet on restrictions, including social distancing and mask mandates.

“We are heading in the right direction, but it is important not to relax our restrictions or get overconfident,” he warns.

Last’s study was presented virtually at the International Conference on Artificial Intelligence in Medicine (AIME) on August 26.

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