Israeli Information Suggests Attainable Waning in Effectiveness of Pfizer Vaccine

As Israel grapples with a new surge in coronavirus cases, its Ministry of Health reported Thursday that while the effectiveness of the Pfizer BioNTech serious disease vaccine remains high, its protection against infection by the coronavirus compares to this Winter and early spring may have subsided significantly.

When analyzing the government’s national health statistics, researchers estimated that the Pfizer syringe was only 39 percent effective against infection in the country in late June and early July, compared with 95 percent in January through early April. However, in both periods, the syringe was more than 90 percent effective in preventing serious illness.

Israeli scientists warned that the new study is much smaller than the first and that cases were measured in a tighter window of time. As a result, their estimates flank a much wider range of uncertainties, which can also be skewed by a variety of other factors.

Dr. Ran Balicer, chairman of the Israeli Covid-19 National Expert Advisory Panel, said the challenges in accurately estimating the effectiveness of vaccines are “immense”. He said more careful analysis of the raw data is needed to understand what is going on.

“I think data should be very careful because of the small numbers,” said Eran Segal, a biologist at the Weizmann Institute of Science and advisor to the Israeli government on vaccines.

Still, the new estimates raise concerns both in Israel and elsewhere, including the United States, that the vaccine may lose some of its effectiveness. Possible reasons are the rise of the highly contagious Delta variant or protection against the gunshots that diminishes over time.

Israel launched an aggressive campaign with the Pfizer vaccine in January, and the country has achieved one of the highest vaccination rates in the world, with 58 percent of the population fully vaccinated. At the beginning of the campaign, government researchers began assessing how much the shot reduced people’s risk of developing Covid-19.

They released their results in May based on records from January 24th to April 3rd. They estimated the vaccine was 95 percent effective in preventing infection from the coronavirus in the country. In other words, the risk of developing Covid-19 was reduced by almost 100 percent in vaccinated people compared to unvaccinated people. The researchers also estimated that the vaccine was 97.5 percent effective against serious illnesses.

From a peak of over 8,600 cases per day in January, cases declined in the months that followed until only a few dozen people tested positive daily across Israel. The vaccine most likely played a role in this decline, along with the strict restrictions the government placed on travel and meetings.

Israel began easing its restrictions in the spring. Cases rose again at the end of June. Now over a thousand people are testing positive every day, causing Israel to restore some restrictions this week.


July 24, 2021 at 11:34 a.m. ET

Some of the people who tested positive for the coronavirus in the new surge were fully vaccinated. Epidemiologists had expected such breakthrough infections, as with all vaccines.

Health Department researchers re-examined the vaccine’s effectiveness and limited their analysis to the June 6-July 3 surge. During this period, they estimated the vaccine’s effectiveness in preventing infections had dropped to 64 percent.

More recently, they did another analysis. This time they investigated cases between June 20th and July 17th. During this period, they estimated that the vaccine was even less effective: only 39 percent against infection.

Still, they estimated that the major disease vaccine effectiveness remained high at 91.4 percent.

If a vaccine is 39 percent effective, that doesn’t mean 61 percent of those vaccinated were infected with the coronavirus. Instead, the risk of infection is 39 percent lower for those who have been vaccinated than for those who have not been vaccinated. Even at this lower percentage, the data show that vaccinated people have a significantly lower risk of infection than unvaccinated people.

The small number of people in the latest study means the actual effectiveness could be lower or higher. The numbers are made even more uncertain by the fact that the new increase has not yet spread evenly across the country. Travelers who ingested the highly contagious Delta variant have brought it back to areas where vaccination rates are relatively high.

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The new outbreaks have yet to flood communities of Orthodox Jews or Arab Israelis where vaccination rates are lower. This imbalance can make the vaccine appear less effective than it really is.

The age of the vaccinated persons also varied considerably in the various periods examined. For example, the people who were vaccinated in January were different from those who received them in April in one important way: They were over 60 years old. If more people who were vaccinated in January become infected now, it may not have anything to do with it. to do the vaccine themselves, but with their advanced age – or some other factor that researchers have yet to consider.

Still, the new estimates made some researchers think about what could happen to the vaccines. The Delta variant became increasingly common in Israel in June, raising the possibility that it might well escape the vaccine.

In the UK, where Delta started rising earlier this year, researchers estimated the effectiveness of the Pfizer BioNTech vaccine against the variant based on a review of everyone in the UK who were vaccinated by May 16. On Wednesday, they reported in The New England Journal of Medicine that it is 88 percent effective against symptomatic Covid-19.

Another possibility is for the Pfizer BioNTech vaccine to gradually lose its effectiveness. The Ministry of Health researchers found that people who were vaccinated in January were more likely to have breakthrough infections than people who were vaccinated in April.

If the vaccine actually wears off after six months, the effects can be huge. It can influence the current deliberations of the Israeli government as to whether the people should be given a third chance. Dr. Segal says it might be wise to introduce boosters to combat the outbreak caused by Delta if the vaccines are actually losing some of their effectiveness.

“If a third booster is safe and it looks like it will be of real benefit, I think we should definitely do it as soon as possible,” he said.

Dr. Balicer, who is also the chief innovation officer at Clalit Health Services, said he and his colleagues are working on their own study of the vaccine’s effectiveness in Israel, using Clalit’s health data to account for such confounders.

“I think it definitely takes off some, but not as much as the rough data suggests, and it’s not just the fault,” said Dr. Balicer. “We’re trying to figure it out cleanly now.”

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