Israel nearing herd immunity threshold, expert says, but some question his claim
Israel’s will soon reach over 1 million COVID-19 cases, including untested infections, and start dropping, predicts Prof. Mark Last, but over 1,000 may still die in coming months
Nathan Jeffay is The Times of Israel's health and science correspondent
Herd immunity is close, and coronavirus cases will soon peak and start falling, but Israel’s death count will increase by 150 percent before the end of the year, according to a new study.
Prof. Mark Last, whose research is being peer reviewed, said a model he developed showed that “we should be at the peak within the next two or three weeks, and start a slow decrease in the number of new cases, assuming there is no change in the current restrictions.”
But at the same time, he warned that until Israel reached that point, infections and deaths would continue piling up. The coronavirus death toll in Israel currently stands at 919, and is rising by about 14 fatalities a day.
“I expect about another 1,300 deaths by the end of the year,” he told The Times of Israel.
Last said that despite the significant number of deaths — roughly similar to the number predicted by coronavirus czar Ronni Gamzu — his research gives cause for “optimism,” as it suggests that hospitals will never exceed capacity, and that infection rates will soon drop.
His claim comes as scientists internationally are revising estimates of how widespread the virus needs to be for of herd immunity — a point at which enough citizens have protective antibodies in order to disrupt the infection chain and significantly slow the spread of the virus.
According to Last, only about one in six Israelis need to have been infected for herd immunity.
According to Health Ministry data published Sunday night, Israelis had racked up just over 114,000 infections since the start of the pandemic. The numbers were likely skewed by 1,000 or so, due to a strike by technicians at publicly funded testing labs.
The number is roughly equal to 1.2 out every 100 Israelis having been confirmed as infected.
But Last argues that given that only a minority of people who are infected go for testing.
According to Last, Israel’s confirmed coronavirus cases reflect just a tenth of the actual cases. He said this assumption is based on international research that has involved populations being subjected to antibody blood tests to show who had the virus at some point.
Last has modeled his statistics over recent months on the logic that only one in 10 of Israel’s coronavirus cases is confirmed, and so far proved accurate.
That means that Israel is only a few weeks away from herd immunity, given the 15% threshold.
A professor unconnected to Last’s study told The Times of Israel that his logic is sound. Prof. Mordechai Gerlic, from Tel Aviv University’s Center for Combating Pandemics, said that Last’s picture of under-reporting matched up with his own.
“Herd immunity will be achieved much faster than people think,” said Gerlic, who is unconnected to Last’s study.
Gerlic, who runs a lab that conducts antibody blood tests for the coronavirus, said Israel has not produced enough data to make a country-specific estimate about how many unconfirmed cases there have been, but based on international studies, this is a fair assumption.
He told The Times of Israel that his own estimate for the number of people required to reach the threshold slightly higher, at one in five Israelis.
Last, a health data specialist and director of the the Data Science Research Center at Ben Gurion University of the Negev, said that his model has proved accurate over the last two months.
But another leading statistician questioned his predictions.
Nadav Katz told The Times of Israel: “It’s good to be optimistic, but the evidence I’m aware of doesn’t support it right now.”
Katz, a professor of physics at the Hebrew University of Jerusalem and part of a specialist COVID-19 stats team, said: “We’re still far away from herd immunity, it’s going to take longer to reach the peak, and I don’t think anyone can really predict the number of fatalities.”
Israeli officials are still considering a possible lockdown over the Jewish holidays, which start on September 17. But according to Last’s research, cases will start to drop before then, and, even without a lockdown, continue to fall.
There is debate among scientists regarding when herd immunity will be achieved. It was widely assumed early in the pandemic that 50% to 60% of a population would need to catch the virus. Now, some experts are putting the figure lower, including Tom Britton, a mathematician at Stockholm University, who estimated 43%, and an international team that suggested 10% to 20% in an article that is not yet peer reviewed.
Last concurs with this low estimate. “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,” he said.
While the jury is still out on how long people retain antibodies for and how long they remain active, he assumes that those who have had the virus will not become infected or pass the infection if they encounter SARS-COV-2.
Last said that local distancing, as well as expected herd immunity, makes him optimistic for Israel. “While another lockdown would certainly reduce infection rates, there is no need at the present time, since social and physical distancing is working to lower infection rates,” he said.
