Pfizer Vaccine Is Just as Effective Against COVID U.K. Strain, Israeli Data Shows

New studies by Israeli HMO based on patient data demonstrate coronavirus vaccine effectiveness in real world

Ronny Linder
Ronny Linder
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A coronavirus vaccine being administered at a Leumit vaccination center in Tel Aviv, this week
A coronavirus vaccine being administered at a Leumit vaccination center in Tel Aviv, this week Credit: Moti Milrod
Ronny Linder
Ronny Linder

The coronavirus vaccines administered in Israel are effective at curbing infection rates, the incidence of serious COVID-19 cases and at protecting against the British variant of the coronavirus, according to new studies conducted by an Israeli health maintenance organization based on real-world data and reported here for the first time.

The first study, conducted by Leumit Health Services on the basis of patient data collected since Israel's vaccination campaign began in December, provides invaluable insight into the effectiveness of the vaccine in the real world, as opposed to efficacy rates measured in the course of controlled experiments in laboratories. According to the second study, the Pfizer vaccine is similarly effective at affording protection against the U.K. variant – which is becoming the dominant strain – with respect to the original coronavirus.

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The studies' findings are especially encouraging in Israel, where multiple factors have concocted a situation that is worlds apart from the sterile laboratories where controlled efficacy tests are conducted. Infection rates remain high despite a massive vaccine drive and the country's third nationwide lockdown, amid intensifying social unrest, new and fast-spreading variants and a public split between those who want to be inoculated and those who do not.

"Ten days after [the second dose] there are almost no new confirmed cases,” says Prof. Shlomo Vinker, the head of the medical division at Leumit Health Services, of the first study, explaining that “In the first days following the first dose, there is an increase in the number of confirmed cases since the vaccine is not yet effective. But beginning on the tenth day, you start seeing a drop. When you move to the second dose, you see another downward step, with a further drop a week later."

According to Vinker, the study's findings demonstrate that the vaccine is effective in the real world, protecting both the individual and the wider community. However, he notes that "the vaccine does not afford 100 percent protection" and is less effective “when there are many infected people all around … because one is constantly exposed to the virus."

In conducting the study, Leumit's team collected and cross-analyzed various data points: how many people had contracted the virus after having received at least one vaccine dose, whether they contracted it after the first or second dose, the number of days that lapsed from the last vaccine received. The team also drew on other metrics at their disposal, such as coronavirus test results, and information about the trajectory of each confirmed case, such as whether they became seriously ill or were hospitalized.

Prof. Eran Segal, a computational biologist at the Weizmann Institute of Science in RehovotCredit: Prof. Eran Segal, a computational biologist at the Weizmann Institute of Science in Rehovot

Leumit began to collect and analyze the data on December 20, when Israel's vaccine drive began. According to Vinker, "2,300 of our customers have fallen ill after the first dose, to date. We checked how many sick people and how many vaccinated people there are for each day after the first dose was administered, and then we did the same for the second dose. We then constructed a graph showing the incidence of sick people per 1,000 people inoculated as a function of the number of the days following vaccination.”

U.K. variant

The Pfizer vaccine is similarly effective at protecting against the British variant of the coronavirus, according to the second study conducted in collaboration with Dr. Ariel Yehuda, Leumit's head of research.

Although at first glance it seemed to researchers that most of the people who had contracted the virus after having been vaccinated had been infected by the U.K. variant, which suggested that the vaccine was less effective against this strain, Vinker explains that upon closer examination, this no longer seemed to be the case: “After a complex analysis that averaged different populations, ages and location along a timeline, we concluded that the vaccine protected against the British mutant equally effectively as compared to the original virus.”

The study cross-analyzed some 9,000 samples taken from patients who had contracted the virus since Israel's vaccination campaign began. Laboratory testing allowed researchers to ascertain whether infection had been caused by the British mutant or not.

"Of the 9,000 infected people, 800 had been vaccinated” says Vinker. “That’s not surprising since in the first days after the vaccine there is no protection. The more time elapses, the more protection there is.”

Although Leumit is the smallest of four health funds in Israel, in global terms, it is a large health organization that insures and provides health services for some 730,000 people. According to Vinker, almost 200,000 Leumit patient-clients have received the first jab, with at least ten days having lapsed since 153,000 of them received it, and slightly more than 100,000 of them having received the second dose.

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