The protection offered by the vaccine against Covid-19 decreases after about six months from vaccination and continues to progressively reduce until exposing itself to the risk of incurring the infection, especially where the Delta variant is more widespread. This is what emerges from a study conducted by several Israeli institutions, including the Ministry of Health, published in the New England Journal of Medicine.
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Israel was the first country in the world to launch a mass vaccination campaign against Covid-19. Despite the high rates of vaccination coverage, from June the cases of infection have started to grow again in tandem with the spread of the Delta variant in the country, prompting the government to indicate a third booster dose as early as August.
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The study has now analyzed the infections that occurred during the summer peak, looking at data from 5 million people who had been fully vaccinated with two doses before the summer. Between 11 and 31 July, 13,426 cases of Covid-19 occurred in this population, 403 of which were severe.
“The SARS-CoV-2 infection rate showed a clear increase as a function of the time elapsed since vaccination,” the researchers write. For example, among the over-60s vaccinated in January, the infection rate was 3.3 per 1,000 people, in those vaccinated in February it dropped to 2.2 infections per 1,000 people, and in those vaccinated in March it was as high as 2.2. 1.7 infections per 1,000.
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For the researchers, it is proof that the summer resurgence of Covid-19 was caused, not by the ineffectiveness of the vaccine against the Delta variant, but by a progressive decline in acquired protection: “If there were no drop in immunity, no there would be differences in infection rates between people vaccinated at different times, “they explain.
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The results of the study, according to the researchers, therefore support the decision to start the administration of the third dose of vaccine taken by the authorities of Israel, a country where today there are less than a thousand cases of Covid-19 per day.
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