Study with AstraZeneca reinforces importance of booster dose

As with other COVID-19 immunizers, a booster dose of AstraZeneca vaccine is also required after the complete vaccination schedule. This is indicated by a new study involving Brazil and Scotland, and published in the scientific journal The Lancet on Monday (12/20). The research, of which Fiocruz is part, shows the decrease in vaccine protection over time and in face of the new variants’ emergence.

The assessment, carried out at a time of intense variants of concern circulation and the Omicron emergence, reinforces the importance of the pandemic dynamics surveillance. The follow-up, which is being done by the same group, also reinforces the great benefits observed from vaccination in Brazil, where the Astrazeneca/Fiocruz immunizer has been the most widely used so far with evidence of high effectiveness - as recently published in the Vigivac bulletin.

“Vaccines are very protective, but, in general, the protection decreases with time, and this is not only the case with COVID-19 immunizers. In the case of Influenza, the immunization lasts a year or less. Finding out how long the protection lasts helps to plan better”, explains Manoel Barral Netto, a researcher from Fiocruz Bahia who participates in the research.

The study points out a drop in the vaccine's effectiveness of about three times around the fourth month when compared to the maximum protection period. The data from Brazil and Scotland could be compared because both adopt the same interval between doses, 12 weeks. The conclusions were similar.

“The findings have important implications for the vaccination policy. In combination with immunological and emerging trial data suggesting that the vaccine’s effectiveness decreases with time after the second dose, our findings highlight the need to consider providing booster doses. Further evidence in support of booster doses comes from real-world data in Israel, which found that BNT162b2 booster doses (Pfizer) [after two doses of the same vaccine] were associated with a reduction in the COVID-19 severe form”, the study says.

“We noted that some people have not been looking for the booster dose here in Brazil. It is necessary to insist on this, even more at a time when the Omicron variant is emerging. The research on the Omicron variant is still in its early stages, but we know that a booster dose has been able to protect against the variants that have emerged”, highlights Barral.