The third dose of the covid-19 vaccine became the new chapter in the long political dispute between the federal government and the state of São Paulo. This week, the Ministry of Health announced the start of a new application of immunizing for September 15 in seniors over 70 years and immunosuppressed.
The announcement took the state government by surprise, which rushed to announce its own start: on September 6 for seniors over 60 years. But one detail irritated the management of João Doria (PSDB) and the Butantan Institute: the ministry removed CoronaVac, produced in São Paulo, from the recommendations for the third dose.
Dimas Covas, director of the institute, said that this was not a technical decision. Doria said the state will use “whatever vaccine it has.” The Ministry argues that the immune response increases with a heterologous boost (ie, with a different vaccine).
Studies on the third dose are still recent and most are in pre-print (when they have not yet been peer-reviewed), but they point out that the combination of different vaccines has shown positive results and indicate that messenger RNA vaccines, such as Pfizer and Moderna, they increase the neutralizing antibodies to the virus.
Researchers heard by UOL they advocate mixing doses, but do not rule out CoronaVac and say it is better to apply the third dose with the available vaccine than with the “ideal”.
Studies indicate better response with ‘mixed’ doses
As vaccination against covid-19 only started in December 2020 in some countries, most studies on the third dose began to emerge from May this year and have shown mixed results, but favorable to the mixture of vaccine types.
Preliminary studies done in Germany and Bolivia indicate that mixing different vaccines can yield a “more robust immune response” and that boosting with messenger RNA vaccines has a greater number of neutralizing antibodies.
Another study from China, where the population was mostly vaccinated with Sinopharm — an inactivated virus, such as CoronaVac — also points to a greater degree of protection with a complement of heterogeneous doses and a preference for messenger RNA vaccines.
I believe that the heterologous dose is more effective. There are good results with a third dose of CoronaVac, but interchangeability studies, especially with the AstraZeneca and Pfizer vaccines, have shown that the heterologous dose is capable of generating a superior response in relation to homologous doses.”
Rafael Dhalia, microbiologist at Fiocruz-PE
The Ministry of Health was on the same argument. In the Technical Note justifying the adoption of the third dose, the folder states that patients immunosuppressed transplant recipients showed “important amplification of both cellular and humoral immune response after administration of an additional dose”.
In conclusion, the ministry indicates, “preferably”, messenger RNA vaccines (Pfizer) or, “alternatively”, viral vector (Astrazeneca and Janssen). Those from inactive virus (CoronaVac) are not mentioned.
CoronaVac cannot be ruled out
The studies are still preliminary and there is no consensus. The immunologist Gustavo Cabral, from USP (University of São Paulo), disagrees with the ministry’s decision and indicates that there are studies that show more promising results with CoronaVac than with AstraZeneca.
“What is difficult to get a good result is using the three doses of the same viral vector vaccine. Because the immune response is not just against a piece of the new coronavirus, it is against the entire viral vector. This vaccine needs to reach inside the cell and the immune response often prevents it,” he argues.
Therefore, he says that, although the heterologous strategy makes sense, CoronaVac cannot be ruled out, especially if there are no doses for everyone. “It’s crazy,” he says.
“The third heterologous dose seems to be better, but there is very little data available, the studies are ongoing. What makes sense is to make the third dose soon for those who need it, homologous or heterologous, even with little data”, agrees the virologist José Eduardo Levi, of the IMT-SUP (Institute of Tropical Medicine of USP).
Different sources have complementary results data. There are a number of field studies in other countries that have seen using a different vaccine, but there is also a study in Asia using CoronaVac with very interesting results. So maybe that’s why this dissent between the two views.”
Fernando Spilki, virologist at Feevale-RS
Sought out by the report, the state health department did not send a position on the scientific findings that support the State Immunization Plan until the publication of this report. If you submit a placement, it will be published.