The survey, to be conducted at clinics run by Israeli H.M.O.s beginning in a week or two, is one of the largest efforts yet to determine the prevalence of antibodies to Covid-19. has also announced antibody testing using a representative sample.
The results could aid in deciding how quickly businesses and schools should be allowed to return to normal operations. On Monday, Israel announced that citizens could leave their homes after a 40-day lockdown, but many aspects of economic and social life remain curtailed.
Even more important, officials said, the survey’s findings could spur preparations for any strong resurgence of the virus, perhaps when hospitals and health clinics are also busy with seasonal influenza.
But if the tests show that only a tiny percentage of the population has been exposed, the country’s health system could still be overwhelmed by the spread of Covid-19, Mr. Bar-Siman-Tov said. He said estimates of the percentage of Israelis with antibodies range widely, from less than 1 percent to upward of 10 percent.
But Dr. Yair Schindel, a member of a health ministry task force on the virus who pushed for a large survey, said the Israeli study could produce such evidence. “Part of what we’re trying to achieve here is to answer the questions the W.H.O. is raising,” he said.
But in a bleaker scenario, the survey would reveal that only 1 percent of Israelis have antibodies, in which case the number of people needing intensive-care beds in a future wave could exceed 12,000 — well beyond Israel’s capacity, he said.
The blood tests check plasma for specific iterations of Immunoglobulin-M, or IgM, and Immunoglobulin-G, or IgG, that are created by the immune system in response to Covid-19. While IgM is created quickly as part of the body’s response to infection and dissipates soon, IgG lingers in the body and “represents our memory of our immunity,” Dr. Schindel said.
Patients visiting their clinics for blood tests for ordinary reasons will be asked to allow their samples to also be tested for coronavirus.
They will also be asked to complete questionnaires about whether and when they experienced symptoms, whether they were isolated at home or hospitalized, who among their friends and relatives contracted the virus, and so on.
Those whose blood tests show the presence of coronavirus antibodies will be called back for a standard polymerase chain reaction, or P.C.R., test for the virus, to determine the correlation between viral load and antibody levels, Mr. Bar-Siman-Tov said.
If the nationwide survey shows a large portion of the population has gained immunity, that could prompt the government to ease remaining restrictions faster, Mr. Bar-Siman-Tov said. But he said there was no going back to a stricter lockdown based on the serological tests alone.
Though Israelis have complained about chaos and inconsistency in the way the rules have been developed and enforced, the country has fared relatively well, with only 237 dead and 16,268 cases as of Tuesday afternoon. are 27 in Israel, compared to 213 in the United States.