Covid vaccine, second doses moved to cover people at risk: are lives saved? – Corriere.it

by time news

Is it possible to delay the second dose of Covid vaccines without risking an increase in infections?
The choice made by the English health authorities to favor the first doses is a positive example: from January to today the infections have gone from 55 thousand to 2 thousand per day and deaths from 1,200 to 10 (also thanks to the lockdown). There are about 36 million people vaccinated, including 19 million with two doses. In Italy, the Medicines Agency (Aifa) and the Technical Scientific Committee (CTS) have established that, as regards the mRna-based vaccines, Pfizer and Moderna, the second dose can be administered 42 days after the first, despite the indication of pharmaceutical companies (21 and 28 days respectively). As explained Giorgio Pal, president of Aifa and exponent of the CTS, the effectiveness of vaccines is not compromised if the recall moves to 42 days. Furthermore, this choice allows for the rapid protection of 3 million over 60s with the first dose, who have a significant risk of mortality from Covid. The confirmation comes from a study by the Mayo Clinic in Rochester (USA), published in the British Medical Journal, according to which delaying the second dose of mRna vaccines in under 65s could reduce deaths by up to 20%, thanks to the increase in availability of first doses, provided that the vaccine is at least 80% effective and the rates of daily vaccinations of the population are between 0.1% and 0.3%. According to the researchers, between 26 and 47 deaths per 100,000 people could be avoided.

What kind of protection do vaccines induce?
The activation of the immune system occurs 10-14 days after the first dose and is stronger than that which occurs in those recovered from Covid. The most important role is that of the so-called memory cells, namely B lymphocytes (which stimulate the production of IgG and IgM antibodies) and T lymphocytes (which destroy virus-infected cells). The second dose of vaccine serves to enhance the response of the memory cells. A study published in Science showed that, after recovery from Covid, the immunological memory of B and T lymphocytes remains active for at least 8 months, even in the face of a decrease in antibodies. This is why a low level of antibodies (for example in a serological test report) does not mean lack of protection.


Is it possible to receive the second dose with a different vaccine than the first?
In Italy this unauthorized practice and the WHO itself advises against it, in the absence of conclusive data on the matter. A preliminary study conducted in Great Britain (published in Lancet) shows that using AstraZeneca for the first dose and Pfizer for the second (or vice versa) there was an increase in mild or moderate side effects in the 24-48 hours following the booster (fever, fatigue, headache, joint and muscle pain) compared to people vaccinated with two doses of the same preparation. None of the 830 participants reported severe reactions that required hospitalization.

Can anyone who has received AstraZeneca receive the second dose of the same vaccine without fear?
Yes, the very rare episodes of thrombosis occurred after the first dose, while no episodes were recorded after the booster. In the latest AIFA Pharmacovigilance Report, 29 intracranial venous thrombosis and 5 cases of atypical venous thrombosis were reported after the first dose of AstraZeneca (out of 4 million administrations).

Can those recovered from Covid be vaccinated?
Those who have overcome the infection can receive a dose after 3 months and no later than 6 months. Immunosuppressed people should instead receive the full vaccination course.

(Mario Clerici, full professor of Immunology at the University of Milan and scientific director of the Don Gnocchi Foundation collaborated)

May 13, 2021 (change May 13, 2021 | 23:22)

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