Between 2 percent and 3 percent of the Israeli population has contracted the coronavirus, at least 10 times more than the number of confirmed cases. That is the conclusion of the first Israeli study based on a representative sample of serological (antibody) blood tests.
According to the researchers, this means that as many as 270,000 Israelis may actually have been infected by the virus, most without displaying any symptoms at all. Yet the antibodies in their blood indicate that they’ve been infected.
This paints a decidedly different picture than previous estimates made by other researchers, who believed that the confirmed cases – slightly more than 17,000 as of Monday – constituted the majority of those infected in Israel.
The survey was conducted for the Pandemic Task Force led by Prof. Daniel Cohen of Tel Aviv University’s School of Public Health, in cooperation with the National Center for Disease Control and the Magen David Adom blood service.
The researchers conducted serological tests on blood samples of 1,700 Israelis, culled to form a representative sample of the population in terms of age, gender and geographic location. Some of the blood samples came from healthy people who donated blood to MDA, while others were collected randomly as part of the routine monitoring conducted by the center for disease control (not necessarily to monitor the coronavirus).
The researchers used serological testing kits that have been validated as being 95 percent to 98 percent accurate. During the study the scientists discovered IgG antibodies, the type that appear a week to two weeks after exposure to the virus. When it comes to other viruses, these antibodies are linked to protection from re-infection, but with regard to the coronavirus it still isn’t clear what level of protection these antibodies provide, and for how long.
“The data arising from the survey is generally similar to the information and surveys we’ve seen in other places,” Cohen told Haaretz. “For example, we see that there’s a higher rate of exposure among men than among women. Among women the rate of infection is 1.2 percent, compared to 2.6 percent among men.” The survey also showed that the greatest rate of infection is among ages 40 to 59, with the rate in this age range 3.6 percent. Among those 0 to 19, the rate of infection was 0.8 percent.
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The size of the sampling and the sensitivity of the test lead researchers to believe that between 2 percent and 3 percent of the population is infected – between 180,000 and 270,000 Israelis. This means not only that the number of infected people is far higher than is known, but that in most cases – far more than had been estimated until now – those infected display no clinical symptoms. Nevertheless, Israel is far from a “herd immunity” situation, in which so much of the population has been infected that the spread of the disease will be slowed or even halted. This requires at least 60 percent of the population to have been infected.
“This is the first study in Israel that provides information on the rate of exposure of the general population to the new virus,” says Prof. Lital Keinan-Boker, director of the National Center for Disease Control. “The information indicates that for every known patient, there are between 10 to 15 cases that have not been identified. It’s important to check this with additional samplings of the population, because this is intelligence that’s been missing to date in coping with the disease.”
The question of what percentage of the population has been infected (including those that don’t develop symptoms) is one of the key questions for epidemiologists, because they can learn from this how the virus is spreading and at what pace; obtain more accurate mortality rates, and determine which populations and geographic areas are most affected. A large, nationwide serological survey is meant to begin shortly that will include samples from 150,000 to 200,000 Israelis obtained from the HMOs. A more in-depth serological survey is expected to begin in Bnei Brak, to learn more about the dynamics of the virus’ spread in densely populated areas.
A study conducted recently by Tel Aviv University, based on mapping the genome of the virus and examining the genetic mutations it underwent as it spread, led those researchers to conclude that the rate of infection in Israel was only 1 percent at most, and that it was almost certain that those confirmed cases constituted most of the infections in Israel.
Reports by the team advising the National Security Council, meanwhile, claimed that only 20 percent of those infected show no symptoms and also stated that most of those infected were those who were confirmed cases.