A nationwide serological survey conducted by the Health Ministry from July to September found that 5.5 percent of Israelis have coronavirus antibodies, indicating that the country is far from achieving so-called “herd immunity” from the pandemic.
The study released Thursday indicated that the virus was far more widespread than known, but fell short of assessments that had predicted the pathogen had gone undetected in the vast majority of cases.
According to the study, up to half a million people may have caught the virus, about double the number of cases that had been confirmed by the end of September, and about four times the number who had been confirmed infected at the start of September.
The Health Ministry announcement did not say whether the study had included September, and a spokesperson could not be reached for clarification.
Either figure would still fall well short of predictions. Earlier this month, Dr. Michael Ryan, head of emergencies at the World Health Organization, estimated that one-tenth of the planet may have been infected, some 20 times the number of confirmed cases worldwide. The coronavirus that causes COVID-19 is known to have vastly different effects on people. For some it is fatal, but many others do not experience any symptoms.
Israeli researchers had estimated that only one-tenth of cases had been found here. At the start of September, that would have represented 1.2 million cases.
“The findings of the survey show that the rate of exposure in Israel is far from what could be defined as ‘herd immunity.’ In addition, high rates of antibodies in the blood does not necessarily attest to long-term immunity,” the ministry said, urging Israelis to continue wearing masks, social distancing and washing their hands, even if they were found to have generated antibodies to the virus.
The serological testing program, first announced in May and initially scheduled to begin later that month, had been touted as an important tool in finding the true level of infection in Israel and determining the level of community-wide immunity.
However, the plan was plagued by delays and pared down considerably to 55,000 tests, only launching in July, when infection rates in Israel had ebbed before ramping back up in August. The ministry said it may carry out additional serological surveys in the future.
The study found infection numbers varied widely from community to community and city to city; those in ultra-Orthodox areas were far more likely to have antibodies than the rest of the country, a finding consistent with indications of sky-high infection rates in those communities.
The blood tests collected in hundreds of towns and cities around the country revealed that Jerusalem had the highest rate of past infection, with 9.5% of samples gathered from the capital confirmed to have an immune response to the virus, the Health Ministry said Thursday.
There have been nearly 40,000 confirmed COVID-19 cases in Jerusalem, a city of nearly 900,000 residents, as of Thursday — some 4.5% of its population.
Overall, the rate of antibodies found in ultra-Orthodox areas was five times higher than among other populations, it said. Antibodies were also four times more prevalent among residents of towns and cities flagged as virus hotspots during the first wave of the pandemic in March-May than in low-infection areas, it said.
Men were more likely to have been infected than women (4.9% vs 3.1%), while 8.1% of children had antibodies, the survey found.
In Tel Aviv, just 2.2% had antibodies, while in the Central Israel district, 2.9% did. In the north, just 1.9% showed traces of antibodies, and Haifa had an even lower rate of 1.1%. The rates of past infection were higher in cities than small towns.
Even as it warned that the presence of antibodies did not prove immunity from the virus, the ministry signaled that those exposed in the past could soon be exempted from quarantine requirements.
“It’s possible that a serological test will soon be adopted as a method to identify people who have been infected in the past… to reduce/prevent quarantine for people who had the virus in the past and recovered,” the Health Ministry said.
Infection rates have soared in Israel in recent months, with over 165,000 new cases recorded since September 1, indicating a far larger number of Israelis have since been exposed. As of Thursday, there have been 283,532 cases since the start of the pandemic and 220,046 have recovered. The death toll is 1,846.
In August, an Israeli researcher claimed only about one in six Israelis need to have been infected in order to achieve herd immunity, the point at which the virus can no longer maintain a foothold within a community due to prevalent antibodies. Prof. Mark Last predicted at the time that Israel was just weeks away from herd immunity, though his research was doubted by other experts.
“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,” Last said at the time.
Antibody tests are said to be between 95% and 98% accurate. Research has suggested that antibodies that the immune system makes to fight the new coronavirus may only last a few months in people with mild illness, but their protective powers may remain. Researchers in a recent study found that the antibodies had a half-life of 36 days, which means that half of them would be gone after that much time. It dovetails with a previous report from China also suggesting antibodies quickly fade.
While some policymakers have pinned hopes on herd immunity in the absence of a vaccine, others believe the gamble too risky, especially given unknowns about the threshold needed to achieve it.
The WHO in August scotched notions that 50 percent of people having developed resistance to the new coronavirus would be enough to achieve “herd immunity” and thereby stop transmission. People should “not live in hope of herd immunity being our salvation. Right now, that is not a solution,” said emergencies head Ryan at the time.
The WHO’s chief scientist, Dr. Soumya Swaminathan, in August estimated: “We think it needs at least 60 to 70% of the population to have immunity to really break the chain of transmission.”
Agencies and Nathan Jeffay contributed to this report.