An initial set of serological tests, the first conducted in Israel, has indicated that some 200,000 Israelis, 2.5 percent of the population, have had the coronavirus — more than ten times the confirmed number of patients, a report said Tuesday.
The antibody tests are seen as a key component in finding out who already had the disease in order to better understand its spread and shape policy ahead of a possible second outbreak.
The results indicate a far greater infection rate than previously thought — estimates by the Health Ministry and the National Security Council put the rate at no more than 1% of the population — but still nowhere near the 60% or so that is required to achieve herd immunity. It also indicates a far greater chance than previously thought for carriers to feel no symptoms.
They also indicate that the rate of men who contracted the virus is more than double the rate for women, a far greater gender gap than indicated in the confirmed cases.
The set of 1,700 antibody tests was conducted by a Health Ministry team led by Prof. Daniel Cohen, the acting head of Tel Aviv University’s School of Public Health, with help from the Magen David Adom ambulance service. Those tested are a representative sample of the population in age, gender and place of residence, the Haaretz daily said in its report Tuesday.
Antibody tests are different from the nasal swab tests currently used to diagnose active infections. Instead, the tests look for blood proteins called antibodies, which the body produces days or weeks after fighting an infection. Most use a finger-prick of blood on a test strip. An antibody test might show if the subject had COVID-19 in the recent past, which most experts think gives people some protection.
But studies are still underway to determine what antibody level would be needed for immunity. It is also not yet known how long any immunity might last or whether people with antibodies can still spread the virus.
The reliability of the tests is said to be between 95% and 98%. They don’t say whether the person still has the coronavirus or if they have recovered.
For most viruses, the presence of antibodies confers immunity from future infections. However, in light of reports of people being reinfected with COVID-19, more research is needed to learn what level of protection is granted by its antibodies and for how long.
“The data from the tests is generally similar to information we saw elsewhere,” Cohen told Haaretz. “For instance, we saw there was a higher exposure rate for men than women. Among women the infection rate was 1.2% compared with 2.6% for men.”
Those infection rates would mean that almost 70% of the Israelis who had the coronavirus are men. Among confirmed cases, only about 55% are men.
Data from elsewhere in the world has recorded only slightly higher infection rates for men than women, though the disease tends to affect men more severely than women.
The initial tests also found that the highest infection rate, 3.6%, was recorded among those aged 40-59. Among those up to 19 years old, the rate was 0.8%.
In total, taking into consideration the sample size and the test’s sensitivity, the researchers estimated that about 2-3% of the population has been infected — between 180,000 and 270,000.
A much bigger set of 150,000 to 200,000 tests is planned to start in the coming days, which will give a fuller and more accurate overview of the Jewish state’s outbreak.
A separate study will focus on Bnei Brak, which in the beginning of April was the first city placed under a strict lockdown, with residents only allowed to leave municipal boundaries to work in key industries or to receive medical care.
Though outgoing Health Ministry director Moshe Bar Siman-Tov announced the program in early May, it has faced delays and the ministry has offered little information about the testing, its scope or when it would begin.
The antibody tests come as the country has seen an uptick in COVID-19 cases over the last week, raising concerns of the virus’s resurgence and a possible second wave.
On May 5, Bar Siman-Tov told The New York Times that 100,000 serological test kits were being prepared for use by health clinics across the country within a couple of weeks. Some 2.4 million tests were obtained by Israel from firms in the United States and Italy for almost $40 million, that report said.
Channel 12 said the Health Ministry purchased 2 million tests, of which 250,000 are currently languishing in storage and are set to expire by early July.
The project was held up by disagreements among health officials on how to implement the plan, including on the sample size within the population, work guidelines for labs and recruitment protocols of those being tested.
The serological pilot program will focus on three groups: families where there was a verified patient, symptom-free families living in a building where a verified patient lives, and a random selection of families and individuals in the city.
The government hopes that by conducting such widespread testing, it will be able to determine if Israel is approaching herd immunity or if it is unprepared for a resurgence of the virus.
Bar Siman-Tov has said that if only a small percentage of Israelis are found to have COVID-19 antibodies, that could indicate the country’s health system may become swamped during a future outbreak.
Health experts around the world have regarded antibody tests as an acceptable means of determining lockdown policies and useful for monitoring purposes, even though the World Health Organization (WHO) has not yet declared that antibodies necessarily mean their carrier has immunity from reinfection.
Despite many reports of reinfections — including at least two cases in Israel — and the WHO saying last month that there was no evidence that people who have recovered from COVID-19 and have antibodies are protected against a second infection, most experts say those reports are likely due to problems with coronavirus tests, as opposed to a lack of immunity from reinfection.
Some experts around the world, including a senior official at the World Health Organization, have argued that reports of reinfected patients have been false positives, with the tests picking up on dead virus fragments.
Agencies contributed to this report.