Covid, the study: stronger response with vaccine mixes

Classic vaccination with a single Covid vaccine for first and second dose, or a mix? This is the dilemma they have faced in many, in different countries of the world. In Italy, for example, the under 60 vaccinated with AstraZeneca, for whom the booster was recommended to continue with an mRna vaccine. But which of the two schemes offers the best performance in terms of protection even against Sars-CoV-2 variants? If some researches have highlighted a greater reactogenicity (production of adverse reactions) for the mix, a new study published in ‘Nature Medicine’ explores the immunogenic aspect of the two vaccination protocols under several profiles, one homologous with AstraZeneca and the other heterologous with two shield products: AstraZeneca and BioNTech / Pfizer. And he concludes that although both regimens potentiate both humoral and cellular responses, the group that received the heterologous booster exhibit “significantly stronger immune responses.” The work has as its first authors scientists from the Institute of Immunology, Hannover Medical School (Germany). The experts specify that any confounding factors could not be completely excluded, in any case they analyze various details of the immune response. For example, in the heterologous recall group the subjects were found to have developed higher titers of antibodies to Spike protein of both the IgG and IgA subclasses. Antibodies, which were highly efficient in neutralizing all three variants of concern tested in the study: Alpha first identified in the UK, Beta isolated for the first time in South Africa and Gamma, originally detected in Brazil. On the other hand, it was not possible to collect data on the Delta variant. Another aspect: heterologous and homologous vaccinations instead led to a similar extent to the expansion of memory B cells. As it highlights the importance in any case of the double dose to obtain complete protection from Sars-CoV-2 infection. The data used by the researchers are those of the participants in the cohort of a study – Covid-19 Contact (CoCo) – which involved health workers, healthy and relatively young. Now, they conclude, it will be of particular importance to examine the neutralizing activity against the Delta variant and to measure how long protective immune responses are maintained.