Rome, November 24, 2021 – “From December 1st it will be possible to book and take a booster dose “of the anti-Covid vaccine” above the age of 18 “, announced the Minister of Health Roberto Speranza, during the press conference at the end of the Council of Ministers which approved the decree on the new anti-Covid measures. “In recent days – he explained – we have already made the choice that goes in the direction of an advance on the possibility of having the recall at 5 months. This indication has already been formalized by the Italian drug agency Aifa, the opinion already published in the Gazzetta official and from today it is possible to have the recall at 5 and no more at 6 months “from the second dose. “Now we are preparing a further modification that will be in force from 1 December and that enables us to further expand the registry of people who are entitled to the booster dose. Until now this audience was limited to people with more than 40 years old ”, from 1 December it opens for ages 18 and up.
“We have an advantage, also due to the courageous choices made in the previous months – concluded Speranza – and we want to try to preserve it by anticipating the virus”. The race for the third dose has begun, but it is difficult to understand how long it will protect against the infection. For the virologist Francesco Broccolo, of the Bicocca University of Milan, “no one is currently able to know how long the third dose will last, and it is possible that it may not be the final one”.
The hypothesis, according to the expert, is that “the rapid decay of immune protection could be due to a variant other than the vaccine for which protection is induced”. In other words, the current Covid-19 vaccines have been designed to respond to the original strain of the SarsCoV2 virus, which however has mutated over time, leaving room for Alpha variant, now completely supplanted by the Delta. “Another reason is that, unlike what happens with traditional vaccines, we are inducing a very targeted immunity on protein S”, continues the expert referring to the Spike protein, which is currently the main target of anti Covid vaccines. .
The vaccines we have known so far were instead “constructed with inactivated viruses or with protein subunits”, consequently they target different regions of the virus and not just one. In light of all these uncertainties, the data on the duration of vaccines they are what health authorities and governments are relying on to decide on the third dose. The data of Israel on the Pfizer / BioNTech vaccine, developed by the research institute of Leumit Health Services, are based on data relating to 83,057 adults (mean age 44 years) who between May and September were subjected to a molecular swab at least three weeks after the second dose of vaccine and who had never previously shown signs of SarsCoV2 infection.
The results indicate that, after the second dose of the vaccine, the positivity rate increases over time: it is equal to 1.3% between 21 and 89 days, 2.4% between 90 and 119 days, 4.6% between 120 and 149 days, 10.3% between 150 and 179 days, finally 15.5% after 180 days. Compared to the first 90 days after the second vaccine dose, the risk of infection is 2.37 times higher after 90-119 days, 2.66 times higher after 120-149 days and 2.82 times higher after 150 days .
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