Israeli Data Suggests Possible Waning in Effectiveness of Pfizer Vaccine
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 may have declined significantly compared to this winter and early spring. .
Analyzing national government health statistics, the researchers estimated that the Pfizer vaccine was only 39% effective in preventing infection in the country in late June and early July, compared to 95% from January to early April. In both periods, however, the shot was over 90 percent effective in preventing serious illness.
Israeli scientists have warned that the new study is much smaller than the first 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.
Dr Ran Balicer, chairman of Israel’s National Expert Advisory Group on Covid-19, said the challenges of making accurate estimates of vaccine effectiveness were “immense”. He said more careful analysis of the raw data was needed to understand what was going on.
“I think the data should be taken with a lot of caution due to the small numbers,” said Eran Segal, a biologist at the Weizmann Institute of Science and the Israeli government consultant on vaccines.
Nevertheless, the new estimates raise fears both in Israel and elsewhere, including the United States, that the vaccine could lose some of its effectiveness. Possible reasons include the increase in the highly contagious Delta variant or a decline in shot protection 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% of the population fully vaccinated. At the start of the campaign, government researchers began to estimate how the shot reduced the risk of contracting Covid-19.
They released their results in May, based on records from January 24 to April 3: They estimated the vaccine to be 95% effective in preventing coronavirus infection in the country. In other words, the risk of contracting Covid-19 was reduced by almost 100% in vaccinated people compared to unvaccinated people. The researchers also estimated the vaccine to be 97.5% effective against serious illness.
From a peak of more than 8,600 cases per day in January, cases plummeted over the following months until only a few dozen people tested positive daily across Israel. The vaccine has most likely played a role in that drop, along with the tight restrictions the government has placed on travel and meetings.
Israel began to relax its restrictions in the spring. At the end of June, the cases increased further. Today, more than a thousand people test positive every day, which led to Israel reinstating some restrictions this week.
Some of the people who tested positive for the coronavirus in the new wave have been fully vaccinated. Epidemiologists expected such revolutionary infections, as they do with all vaccines.
Researchers from the Department of Health re-examined the vaccine’s effectiveness, limiting their analysis to the June 6-July 3 wave. During this period, they estimated, the vaccine’s effectiveness in preventing infections had fallen to 64%.
More recently, they did another scan. This time, they reviewed the cases between June 20 and July 17. During this period, they estimated, the vaccine’s effectiveness was even lower: only 39% against infection.
Still, they estimated the vaccine’s effectiveness against serious illnesses remained high, at 91.4%.
If a vaccine is 39% effective, that does not mean that 61% of people vaccinated have been infected with the coronavirus. Instead, it means the risk of getting infected is 39% lower in people who are vaccinated compared to people who are not. So even at this lower percentage, the data shows that vaccinated people are significantly less likely to be infected than unvaccinated people.
The small number of people in the latest study means that the true effectiveness could be lower or higher. What makes the numbers even more uncertain is the fact that the new surge has not yet spread evenly across the country. Travelers who caught the highly contagious Delta variant have brought it back to neighborhoods with relatively high vaccination rates.
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The new epidemics have yet to overwhelm communities of Orthodox Jews or Arab Israelis, where vaccination rates are lower. This imbalance can make the vaccine appear to be less effective than it actually is.
In addition, the ages of people vaccinated vary considerably over the different periods studied. For example, people who received their vaccines in January were different from those who received them in April in one major respect: they were over 60 years old. If more people vaccinated in January are now infected, it may not have to do with the vaccine itself, but with their advanced age – or some other factor the researchers have yet to consider.
Still, the new estimates have made some researchers wonder what could happen to vaccines. The Delta variant became more common in Israel in June, raising the possibility that it may be effective in evading the vaccine.
In Britain, where Delta began to increase earlier in the year, researchers estimated the effectiveness of the Pfizer-BioNTech vaccine against the variant, based on a review of all people in the UK who were vaccinated until May 16. On Wednesday, they reported in the New England Journal of Medicine that it is 88% effective against symptomatic Covid-19.
Another possibility is that the Pfizer-BioNTech vaccine will gradually become less potent. Researchers from the Department of Health found that people vaccinated in January had flare-up infections at a higher rate than people vaccinated in April.
If the vaccine does decline after six months, the implications can be huge. This may influence the Israeli government’s current deliberations on whether to give people a third chance. Dr Segal says that if vaccines do lose some of their effectiveness, it might be wise to deploy boosters to tackle the outbreak caused by Delta.
“If a third recall is safe and if it looks like it would really bring an advantage, I think it’s something that we absolutely should do as quickly as possible,” he said.
Dr Balicer, who is also director of innovation at Clalit Health Services, said he and his colleagues are working on their own study on the effectiveness of the vaccine in Israel, using Clalit’s medical records to take these into account. confounding factors.
“I think there is definitely a decline, but not as much as expected based on the raw data, and it’s not just a decline to blame,” Dr Balicer said. “We are now trying to understand it in a clean way.”
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