Pfizer reinforcement after Coronavac raises effectiveness against Covid to 92.7%, study says

A study published this Wednesday (9), in the journal Nature, points out that a booster dose of the Pfizer vaccine after two of the Coronavac increases the effectiveness against the coronavirus to 92.7%.

According to the publication, with the same vaccination schedule it is possible to prevent the worsening of Covid-19 — deaths and hospitalizations — in 97.3% of cases.

The research was based on the analysis of information from about 14.3 million Brazilians who underwent rapid antigen test or RT-PCR — this was done by about 7.3 million individuals of the same amount. The database was made available by the Ministry of Health.

From February 24, 2020 to November 11, 2021, 23.4 million people were tested for Covid for suspected coronavirus infection, with severe outcomes peaking between February 2021 and April 2021.

Of the 13.3 million tests not eligible for the study, 8.8 million were performed before the vaccination campaign in Brazil. These tests only served to know the status of the participants’ previous infections and were not used in the main analysis.

In addition, 2.6 million tests were performed on children under 18, an age group not included in the survey.

Everyone aged 18 and over who reported symptoms similar to those of Covid-19 and underwent a coronavirus test between January 18 and November 11, 2021, was eligible for the study.

From the sample, those vaccinated with Coronavac total 913,052. Of these, 7,863 received a booster dose of Pfizer. Most (93.4%) were tested 30 days after the booster.

According to previous studies with Coronavac, compared to non-vaccinated, from 14 days to one month after applications, the immunizing efficacy was 55% against classic infection and 82.1% in serious outcomes.

After six months, the protection rate dropped to 34.7% and 72.5% against worsening cases.

“You take the two doses of Coronavac and you have protection mainly for serious illness, more or less what we knew. After six months, that protection drops and then, when the person takes the third dose of Pfizer, that protection reaches a level very high, both for uncomplicated infection and for severe disease”, explains Guilherme Werneck, a researcher at the State University of Rio de Janeiro and one of the authors of the study.

“Coronavac is a great vaccine, but protection wanes over time, so Pfizer’s third dose is critical to providing protection especially for severe Covid.”

For the population aged 80 years and over, immunization with three doses is very important. “The protection with the second dose for the elderly was not so good and they were unprotected, but they reached a high level again when they received Pfizer”, says Werneck.

The report asked the researcher about the duration of protection offered by Pfizer, but it is still too early to get an answer, as there is a need for a longer follow-up, according to Werneck.

In all, the study published in Nature had the participation of 14 scientists from Brazilian and international universities.

Other studies

A study by the Ministry of Health carried out in partnership with the University of Oxford shows that the booster dose with the Pfizer vaccine increased the number of neutralizing antibodies by 175 times.

The number is almost three times greater than that of other immunizing agents applied in Brazil. With the AstraZeneca vaccine the increase was 85-fold and with the Janssen vaccine, 61-fold.

Coronavac had the lowest immune response, with a seven-fold increase in neutralizing antibodies.

In another study, released in December last year, Israeli researchers said that applying three doses of Pfizer’s Covid vaccine offers significant protection against the micron.

The research, carried out by the Sheba medical center and the Central Virology Laboratory of the Ministry of Health, compared the blood of 20 people who received two doses 5 to 6 months prior to December with the blood of the same number of individuals immunized with the dose of booster a month ago.