Mixing Covid-19 vaccines in the 2nd and 3rd doses can boost immunity, says Pfizer researcher

Mix vaccines against Covid-19 at the time of the second or third dose it may increase immunity. This is what Cristiano Zerbini, coordinator of the clinical trial of the vaccine at Pfizer in Brazil, says. “Two doses of Pfizer’s vaccine give 88% protection against the Delta variant, for example, while two from AstraZeneca give 77%. Now, if you take one from AstraZeneca and then one from Pfizer, you will get almost the same protection as Pfizer. This interchangeability is good”, said Zerbini, in an interview with CNN.

The same should apply to booster doses, which are widely discussed not only in Brazil, but worldwide, with the emergence of new variants of the coronavirus. Recent research carried out by Janssen shows that the application of an extra dose of the company’s vaccine, originally applied once, can increase antibodies up to nine times – without necessarily the first application having been of the vaccine produced by the Belgian pharmaceutical company. This indicates that, in theory, whoever took two doses of Coronavac could take a third of Janssen as a backup. Studies still need to be done to confirm the interchangeability between the two immunizers.

“This has not yet passed through Anvisa. But we know that studies carried out abroad show that a second dose produces antibodies in very high numbers”, says Zerbini.

Regarding Pfizer’s vaccine, made with messenger RNA, the third booster dose of the vaccine against Covid-19 should start in September this year for elderly and immunosuppressed people.

Before that, however, Zerbini warns: it is necessary to carry out stronger and more effective vaccination campaigns so that Brazilians take the second dose of vaccines. Immunity with just one dose exists, but it is much lower than with the correct doses. “The first dose gives good immunity, but much less than when taking the second dose. We need to think about the application of the second dose and, especially, the third dose for the elderly and immunosuppressed people — such as those who had cancer and are undergoing treatment, those on kidney dialysis and those who had autoimmune diseases”, he says.

Regarding the booster dose, Zerbini calculates that Brazil has around 4 million people over 80 years old and “more or less” 4 million people with a degree of immunosuppression. Another urgent step, for the specialist, is to vaccinate adolescents and children. “If we don’t immunize everyone, we will generate other variants — and this will be a serious problem”, he says.

When it comes to taking the second or third dose, for Zerbini, the vaccine manufacturer doesn’t matter. “The second dose or the third dose can be given with the available vaccine. And it is important that all Brazilians take at least the second dose”, he says.

To facilitate the production of Pfizer vaccines in Brazil, an agreement was signed with Euroforma. Zerbini believes that this “will facilitate the logistics and may reduce the price of the immunizing agent”. Next year, he said, vaccine trials against a flu vaccine based on messenger RNA could be started.

*Produced by Layane Serrano and Thiago Félix, from CNN São Paulo