Third dose, Abrignani: “With recall, protection returns to 90%, hopefully last years”

The administration of the third dose of the anti-covid vaccine, which started yesterday for the frail categories “is not a change of strategy. It was to be taken into account that it would have been necessary to strengthen the immunological memory produced by only two close doses of vaccine”. This was stated by Sergio Abrignani, immunologist of the State University of Milan and member of the technical-scientific committee, in an interview with ‘Il Corriere della Sera’. “In the history of vaccines, boosters with a third dose spaced several months in time are the norm – he adds – Why didn’t we immediately establish that two inoculations had to be followed by a third? There was a need to have the vaccines as soon as possible and waiting another 6-8 months to conclude a triple dose trial would have meant resigning oneself to seeing so many other people die “. Isn’t that a fallback, an admission by science of not having planned well? “This is not the case at all. The two doses of vaccine confer protection and also respond to the Delta variant – replies Abrignani – But it has been seen that, like most of the close cycles, they induce a short-term immune response and therefore protection after 6- 8-months it is reduced from 90 to 60% approximately. With a third booster, after at least 6 months, not only is the efficacy brought back to initial levels but we hope, in analogy with many other vaccines, that it will last for years ” .No fourth dose, are you sure? “With this virus, nothing is certain. Let’s wait to see if and when those who receive the third dose today will be reinfected. But the experience with many other vaccines (such as those for hepatitis B, meningococcus B, poliomyelitis, haemophilus, tetanus, diphtheria, pneumococcus, pertussis) gives us hope that further recalls, if necessary, will affect us after 5-10 years “, recalls the immunologist. Will the third dose be equivalent in quantity of active ingredient to the previous two? “Yes, because we speak in terms of micrograms, minimal quantities compared to those of drugs. It takes very little to trigger the immune system response”, recalls Abrignani. Will those who have been vaccinated with two doses of AstraZeneca be able to switch to Pfizer and Moderna, the messenger RNA compounds that will be used for boosters? “Yes, it has been shown that heterologous vaccination, with two different products, does not give side effects superior to the homologous one”, highlights. Is the third dose safe? “According to the data coming from Israel, the possible side effects are comparable to those already observed after the second dose. Nothing different and worrying”, he concludes.