As Israel grapples with a new wave of coronavirus cases, its health ministry reported on Thursday that although the efficacy of the Pfizer-BioNTech vaccine remains high against serious illness, its protection against infection with the coronavirus has declined significantly compared to this winter and early spring.

Analyzing national government health statistics, the researchers concluded that Pfizer’s vaccines, while giving vaccinated people 90% lower risk of serious illness, gave them only 39% lower risk of infection. late June and early July, compared to 95% from January to early April. .

Israeli scientists have warned that the new study is much smaller than May’s and measured cases within a narrower window of time. As a result, a much wider range of uncertainties surround their estimates, which could also be skewed by a variety of other factors.

Nonetheless, the new estimates raise concerns in Israel and elsewhere, including the United States. Possible reasons for the apparent loss of efficacy against infection include an increase in the highly contagious Delta variant or a decrease in protection against injections over time.

Dr Ran Balicer, chairman of Israel’s National Expert Advisory Group on Covid-19, said the challenges of making accurate estimates of vaccine effectiveness are “immense”. He said more careful analysis of the raw data was needed to understand what was going on.

Israel launched an aggressive campaign with the Pfizer vaccine on December 20, and 58% of the population is now fully vaccinated, one of the highest rates in the world. Cases have risen 165% in the past two weeks, but hospitalizations, a measure of serious illness, continue to decline, according to Our World in Data, a University of Oxford project.

The vaccinations, coupled with the government’s tight restrictions on travel and meetings, have reduced the country’s daily case count from a peak of more than 8,600 cases per day in January to a few dozen.

Israel began to relax its restrictions in the spring. At the end of June, with the spread of the Delta variant, cases increased again. Today, more than 1,000 people test positive every day, including those who have been fully vaccinated. Epidemiologists expected such revolutionary infections, as they do with all vaccines.

Adding to the uncertainty of the new findings, the push has not spread evenly across the country. Some travelers infected with the highly contagious Delta variant have brought it back to neighborhoods with relatively high vaccination rates, while new epidemics have yet to overwhelm Orthodox Jewish and Arab-Israeli communities, where vaccination rates are low. weaker. This imbalance might seem to make the vaccine less effective.

Also, the people vaccinated at the start of the campaign were over 60 years old; those who had them later were younger. Infections among those who were vaccinated early may have more to do with their age, or some other factor the researchers have yet to consider.

However, if the vaccine’s protection against infection does wane after six months, the implications could be huge, including on deliberations on whether to give people a third injection.

Dr Balicer said he and his colleagues at Clalit Health Services, where he is the director of innovation, were working on their own study on the effectiveness of the vaccine, using Clalit’s healthcare records to take into account. account for these confounding factors.

“I think there is definitely a decline, but not as much as expected based on the raw data,” Dr Balicer said, noting that other factors may be at play. “We are now trying to figure it out d ‘a clean way. “