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The study by Israel’s Clalit Research Institute and Harvard confirms research showing a fading of the COVID vaccine’s effectiveness after a few months.

Starting a week after the third dose of the COVID-19 vaccine, patients have a 92% lower risk of severe COVID and an 81% lower risk of COVID-related death, scientists from Israel’s Clalit Research Institute and Harvard University have found.

These patients also have a 93% lower risk of COVID-related hospitalization, the researchers said in an article published in The Lancet on Friday night. Israel is predominantly using the Pfizer-BioNTech vaccine.

The scientists analyzed anonymous data from over 728,000 patients of Clalit Health Services – one of Israel’s four health maintenance organizations – who received the booster shot. The researchers compared these Israelis to an equal number of patients who had gone more than five months since receiving the second dose. The data covered vaccinated patients between July 30 and September 23.

Also, based on an analysis of the general population, the researchers found that infection rates fell across all age groups within seven to 10 days of each group’s eligibility date to receive the booster.

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The researchers say the correlation between the results of the two analyses increases the certainty of the studies’ accuracy. This is because the two studies used different methods, one at the patient level and one at the general-population level.

“The extensive nationwide rollout of Israel’s third-dose ‘booster’ COVID-19 vaccination campaign provided the Clalit Research Institute with a unique opportunity to assess, through its rich and comprehensive digital datasets, the effectiveness of the third dose in a real-world setting against the less common but severe complications of COVID-19,” Prof. Ran Balicer, the senior author of the study, said in a statement. Balicer is also the head of the Clalit Research Institute and chief innovation officer at Clalit Health Services.

“These results show convincingly that the third dose of the vaccine is highly effective against severe COVID-19-related outcomes in different age groups and population subgroups, one week after the third dose. These data should facilitate informed policy decision-making,” said Balicer, who is also chairman of Israel’s National Expert Advisory Team handling the coronavirus crisis.

Prof. Ben Reis, a predictive medicine expert at Boston Children’s Hospital and Harvard Medical School, said that so far “one of the main drivers of vaccine hesitancy has been a lack of information regarding the effectiveness of the vaccine. This careful epidemiological study provides reliable information on third-dose vaccine effectiveness, which we hope will be helpful to those who have not yet decided about vaccination with a third dose.”

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Clalit’s study confirms research showing a fading of the vaccine’s effectiveness and patients’ antibody levels after a few months. It also confirms that the booster restores immunity comparable to a fresh vaccination, even against the delta variant.

Last month, a study by the Technion technology institute and the KSM Maccabi Research and Innovation Center found that the Pfizer-BioNTech booster significantly reduces viral load in people infected with the delta variant, thus reducing the chance of transmission.

According to the researchers, the vaccine’s effectiveness at shrinking viral load dissipates about six months after the second dose. But they found that a third dose slashes viral loads by four, restoring the vaccine’s effectiveness to its level shortly after the second dose.

That research appears on the MedRxiv website for papers that have not yet been published in a scientific journal. The researchers analyzed 11,000 PCR swab tests by the Maccabi HMO on people who had been infected with the delta variant.

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These patients were divided into three groups – people who were never vaccinated, people who were infected within six months of the second dose and people who were infected after receiving the booster shot.

“We discovered that the vaccine’s effectiveness regarding viral load gradually wanes over time, until after six months [viral load] reaches a high level, similar to that of an unvaccinated person,” said Matan Levine-Tiefenbrun, a doctoral student at Tel Aviv University who is also affiliated with the Technion and was the lead researcher.

The Technion-KSM study came on the heels of a study appearing a few days earlier in The New England Journal of Medicine.

The researchers in that study, using data on over 1 million Israelis 60 and older, found that at least 12 days after the booster, the infection rate in the non-booster group was 11.4 higher than in the booster group, with the rate of severe illness 19.5 times higher.


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