Why and when the third dose of the coronavirus vaccine will be given

Why and when the third dose of the coronavirus vaccine will be given
Why and when the third dose of the coronavirus vaccine will be given

The goal is to vaccinate 80% of the population in September, 54.3 million Italians, including 12-15 year olds. And herd immunity is a goal that is beginning to be seen and that could become a reality very soon in some regions: Campania on August 20, while the national average is set at around 31. Abruzzo and Lombardy on 24, Puglia on 26, Molise on 29, Lazio on 30. All the others in September. But to complete the immunization “at least one more dose may be necessary”, as the emergency commissioner Francesco Paolo Figliuolo admitted yesterday. That is the third for vaccines that require booster or the second for single-dose such as Johnson & Johnson’s Janssen.

Why and when the third dose of the coronavirus vaccine will be given

The third (or second) dose will be administered when the effect of the first cycle, probably at the end of the year for the first immunized, decreases. And it will require a booster with the new vaccines at that point already reset in anti variant mode. But what exactly is the third dose of the coronavirus vaccine for and when will it be done? It all starts with the problem of the duration of immunization. To date, no one can say for sure how long the protection will be valid even if, explains today the Corriere della Sera, Phase 3 studies that started 8-9 months ago tell us that vaccinated people are still protected and that in Britain and Israel, where vaccinations started in December, the protection given by the first vaccinations is still valid.

In addition, the newspaper explains, we do not know the correlation of protection, or the numerical level of immune response that is decisive for establishing immunization or the possibility of still being infected with the Sars-CoV-2 coronavirus. In theory, exposure of vaccinated people to the virus “refreshes” the immune memory and raises antibody levels. For this we are based on empirical data deriving from the continuous measurement of the immune response over time (antibody and T lymphocytes) and the number of infections in the population already fully vaccinated. The immune response decreases over time but it is not known where the protection falls.

For this reason, vaccine boosters are studied, which can be of two types: homologous, or against the same virus, or heterologous. In the second case, which is typical of viruses such as influenza, the vaccine must be reformulated every year to combat a different viral strain. If the recall is homologous, it means that the immune response is rapidly fading. If it is heterologous, then it will be necessary due to the new variants. That they may have found a way around the serum protection in the meantime.

Which vaccines may require the third dose and which not?

What vaccines may require the administration of the third dose? Are there any serums that could maintain the same high protection? The answer to date is impossible. And therefore, as Sergio Abrignani, immunologist of the University of Milan explains, “we must take into account that many vaccines in use are products on which there is no experience: messenger RNA drugs (such as those from Pfizer and Moderna) are not existed before, viral vector vaccines (such as AstraZeneca and Johnson & Johnson) did exist, but they had never been used extensively to vaccinate entire populations. We don’t know if one type of vaccine will provide a longer lasting memory than another. “

To date, for the third dose, a time horizon is imagined ranging from 6 to 9 months up to a maximum of twelve. Nicola Coppola, full professor of infectious diseases and director of the division at the Polyclinic Vanvitelli in Naples, says today in the Morning that already in September the topic could end up on the commissioner’s table because nine months will have passed since the first dose administered to doctors and health personnel. Also according to Anthony Fauci a booster of the vaccines will be necessary within twelve months. And, according to Coppola, it might be a good idea to give a different vaccine as a third dose than the two with which the first and the booster was made. Alternating adenovirus vaccines such as AstraZeneca and Johnson & Johnson with mRna vaccines such as Pfizer-BioNTech and Moderna. And this is in order to induce a stronger immune response.

The mix with the second dose, in the few studies in which it was analyzed, has not yet found any particular contraindications. Certainly Britain has announced the start of the first large-scale trial of the effectiveness of the vaccine booster against the coronavirus. AstraZeneca, Pfizer, Moderna but also Novavax, Valneva, J&J and Curevac will be used in the trial. In the US, the experimentation of the third dose has already started. With a lower dosage and against the South African variant. A few months will be enough to have a definitive answer.

Because after the case of the 18-year-old with thrombosis, the AstraZeneca vaccine should only be intended for over 60s

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