COVID-19 Fiocruz vaccine is effective against Delta variant

Effectiveness studies of COVID-19 vaccines have demonstrated the immunization importance for protection against severe cases and hospitalization against the new variants. In June, data showed a 92% effectiveness of the AstraZeneca vaccine for hospitalizations against the Delta variant. Now, a new study coordinated by Oxford University in the United Kingdom points out that the Pfizer and AstraZeneca vaccines, this one produced in Brazil by Fiocruz, also guarantee protection against infection with the Delta variant of COVID-19.

Conducted in partnership with the UK's Office for National Statistics (ONS) and the Department of Health and Social Welfare (DHSC), the survey analyzed 2,580,021 tests from 384,543 people over the age of 18 between December 1, 2020 and May 16 of this year, when Alpha was the main variant circulating in the UK; and 811,624 tests from 358,983 participants from May 17 to August 1, when Delta was already prevalent in the country. Published in preprint form, the analysis concluded that two doses of both vaccines provide at least the same level of protection as if the person had previously contracted Sars-CoV-2. The immunity guaranteed after Pfizer's and AstraZeneca's second doses differs: Pfizer's initial great effectiveness in protecting against high viral load and infection reduces over time. The results suggest that after four or five months the effectiveness of the two vaccines would be similar, and that Pfizer would lose its effectiveness against infection at a faster rate than AstraZeneca, which has its effectiveness sustained for longer. In the 18 to 64 age group, for example, Pfizer's effectiveness rate dropped by about 22% every 30 days after the second dose. With AstraZeneca, the reduction was significantly less, about 7% every 30 days after the full vaccination regimen.

There is no evidence that effectiveness may vary with the interval of dose application, and protection was greatest among those vaccinated who had previously contracted COVID-19. For example, 14 days after AstraZeneca's second dose, the effectiveness rate against infection was 88% in those who had already contracted the virus, versus 68% in those who had never had the disease; among those immunized with Pfizer, it was 93% and 85% respectively.

The effectiveness against the disease after the second dose was shown to be higher also among younger people. In Pfizer's case, it was 90% in the 18-34 age group, and 77% from 35 to 64. With AstraZeneca, 73% were observed among younger people versus 54%.

Prior studies

A study by Public Health England (PHE) showed, this June, that applying two doses of the AstraZeneca vaccine results in 92% effectiveness against hospitalization due to the Delta variant. In the research, the average effectiveness regarding hospitalization rate for Delta vaccinees was similar to that of Alpha, taking both immunizers into account: Alpha with 78% (one dose) and 92% (two doses); Delta with 75% and 94% (respectively).

In Pfizer's case, the vaccine averaged 94% effectiveness after the first dose and 96% after the second against Delta variant hospitalization. AstraZeneca reported 71% effectiveness after the first dose and 92% after the second.