After 6 months, CoronaVac’s protection falls ‘significantly’, shows study commissioned by the Ministry of Health

SAO PAULO — Partial results of the study commissioned by the Ministry of Health on the third dose for people vaccinated with CoronaVac for Covid-19 indicate that, six months after application, there is a “significant drop” in the levels of total antibodies and neutralizing antibodies.

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The analysis of the data ends this month and should be published in a scientific journal in December and, therefore, the numbers cannot yet be released. But the study coordinator, Sue Ann Clemens, responsible for bringing the Oxford/AstraZeneca vaccine studies to Brazil, head of the scientific committee of the Bill and Melinda Gates Foundation, and director of the first master’s degree in vaccinology in the world, at the University of Siena, said that the study scientifically proves what experts have already warned:

— Antibody levels fall in all groups, especially among the elderly. It’s significant – he says.

The study, with 1,200 volunteers, from Hospital São Rafael, in Salvador, and from the Federal University of São Paulo (Unifesp), also verified the effectiveness of a booster dose for these individuals using vaccines available in Brazil: Pfizer, Oxford/AstraZeneca , Janssen and CoronaVac itself.

– All vaccines stimulated the immune system, but the heterologous booster, that is, made with a different vaccine, is substantially greater – says Clemens.

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The best result obtained was with Pfizer, followed by Oxford/AstraZeneca, then Janssen and finally CoronaVac. Messenger RNA or viral vector vaccines (the first three) also promote greater cellular immunity, which is not the strong point of the inactivated virus vaccine, CoronaVac.

— This corroborates what has been seen in practice, with an increase in cases in the vaccinated group after six months, and in the effectiveness studies that have been carried out. This is the recommendation, although there are states still giving the third dose of CoronaVac in Brazil, which is only justified if the others are not available. We are talking about evidence-based health policy.

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The study has ended, but researchers can submit an amendment in order to take blood samples from the volunteers within six months. Clemens’ expectation is that, with heterologous vaccination, the duration of protection will be longer. There is also the intention to evaluate the possibility of using a half dose for booster, doubling the vaccination capacity.