Against Omnic, Studies Suggest Boosting Pfizer or Astrazeneca After Coronavac

Two new studies bring more evidence in favor of the so-called vaccine mixture (heterologous scheme) in vaccination against Covid.

The studies, conducted in Brazil, evaluated the real-life efficacy (or effectiveness) of vaccines to protect against symptomatic Covid (having or not having Covid symptoms), hospitalization and death, and the protection provided by neutralizing antibodies (capable of blocking the entry of the virus into the cells) in the omicron period.

Despite being two independent studies, the findings were similar: two doses of Coronavac followed by a third dose of the same immunizing agent (called a homologous regimen) confers low protection, while an additional dose of Pfizer or Astrazeneca is more effective against symptomatic cases, hospitalization and deaths, in addition to conferring a high production of neutralizing antibodies.

The two studies compared the effectiveness and protection of the omicron with those conferred for the delta variants and the ancestral form of Wuhan.

The first survey, published last Thursday (6) in the scientific journal Nature Communications, evaluated individuals with a positive RT-PCR or antigen test result for the coronavirus and with those with a negative result from a total of 1.24 million tests. , from September 2021 to April 2022. Data from this study had already been released in April.

Scientists have found a significant drop in the effectiveness of Omicron vaccines for both symptomatic Covid and for hospitalization and death, across all vaccines. This drop, however, was greater for subjects who received three doses of Coronavac compared to those who received two doses of Coronavac and the Pfizer or Astrazeneca booster.

The second study, also released on Thursday (6) on the medRxiv platform in the form of a pre-print (still without peer review) compared the levels of antibodies produced against the Spike S protein (or spike, used by the virus to enter the cells), against receptor binding region (known by the acronym RBD) and neutralizing antibodies up to 28 days after a booster dose in subjects who received two doses of Coronavac from November 2021 to February 2022.

The results indicate that in those with the homologous regimen, the production of neutralizing antibodies against the Ômicron variant was very reduced.

On the other hand, in people who received two doses of Coronavac and a third dose of Pfizer or Astrazeneca, there was an increase in the rate of antibodies of the three types (anti-Spike, anti-RBD and neutralizing), including those specific against the omicron.

When separated by age group (older or younger than 50 years), the production of antibodies after three doses of Coronavac was more pronounced in the younger ones, although it was also lower than in individuals with a heterologous vaccination schedule.

The infectologist and researcher at Fiocruz Julio Croda, who participated in the two studies, explained that both provide evidence for the best use of vaccines currently in use in the country.

“While real-life efficacy data indicate that the third dose, especially for older people, should be a heterologous regimen, laboratory data give the first results on humoral protection. [de anticorpos] against Ômicron, indicating a significant reduction of the Coronavac antibodies against Ômicron, even with three doses”, he says.

With the omicron, vaccines around the world had their efficacies reduced, especially in protecting against infection. However, some vaccines have a much more marked reduction than others when compared to protective antibody responses.

The cellular response, an important defense mechanism of our body, has not been evaluated and should maintain good levels of protection, especially against hospitalization and death, say experts.

“There is an anti-Spike and anti-RBD antibody protection, but it is more pronounced for the ancestral variant, whereas for the VOCs [variantes de preocupação] neutralizing antibodies are more important. In this context, a heterologous booster is most effective in individuals vaccinated with Coronavac,” he explains.

For him, these data are important, as they can help coordinate vaccination strategies. “Of course, any vaccine is better than no vaccine, so in groups that have not yet been vaccinated, such as children aged 3 to 4 years, a primary regimen with Coronavac is better than none at all. But in adults who have already received two doses it is more efficient that the third dose is different”, he says.