The reduction in immunity against Sars-CoV-2 recorded 75 days after the second dose of Coronavac and ChAdOx1 (Oxford-Astrazeneca) vaccines can be significantly reversed with the Pfizer/Biontech booster, according to a study conducted at Escola Paulista de Medicina , from the Federal University of São Paulo (EPM-Unifesp).
Research has shown that the third dose of Pfizer increases the antibody level measured after two applications of Coronavac by up to 25 times and by up to seven times that achieved after full immunization with ChAdOx1. The results were published in the Journal of Infection.
Supported by FAPESP through two projects (17/20106-9 and 20/08943-5), the study was carried out with a non-randomized cohort of 48 health professionals from regional hospitals and institutions. They have an average age of 30 years for those vaccinated with Coronavac and 40 years for those receiving ChAdOx1.
“We have seen that adherence to the booster dose of the Covid-19 vaccine is not as high as it could be. Our study, however, shows the importance of the population taking the third dose because there is a significant increase in the immune response and cell, indicating higher levels of protection” Alexandre Keiji Tashima, professor at the Department of Biochemistry at EPM-Unifesp and corresponding author of the article, tells Agência FAPESP.
Until March 1, Brazil had 30.6% of the population immunized with the booster dose against Covid-19 (about 65.073 million people). With complete vaccination (two doses or a single dose) were 73% of Brazilians (155.071 million people), according to data from Our World in Data, from the University of Oxford, in the United Kingdom.
“With the pandemic, we set up a group of researchers at Unifesp to work on studies involving Covid-19. The objective is to carry out a complete biochemical characterization of the antibodies”, says Tashima, who is a doctoral advisor to Jackelinne Yuka Hayashi, first author of the article. The work also had the participation of four researchers from Euroimmun Brasil, a company specialized in solutions for laboratory diagnosis.
The group’s results corroborate studies already published by scientists from Hong Kong and from North American universities.
In addition, other research had shown the effectiveness of the booster dose. One of them, published in early February in Nature Medicine, showed that the application of the third dose of Pfizer vaccine six months after immunization with two of Coronavac confers an efficacy of 92.7% against the disease. Already against severe cases of Sars-CoV-2, protection rises to 97.3%. Data from about 14 million Brazilians were analyzed.
Assessments
Research participants from the Unifesp group had blood samples collected at five times: before vaccination; 28 days after the first dose; 14 days after the second dose, 75 days after the second dose and 14 days after the third booster. Clinical tests were performed for IgG (which determines the presence and amount of antibodies in the body), with evaluation of neutralizing antibodies, capable of preventing infection, and cellular responses.
In the group immunized with Coronavac and Pfizer booster, mean IgG values increased from 19.8 BAU/ml (binding antibody units per milliliter of blood) after the first dose to 429 BAU/ml with the second. Values equal to or above 35.2 BAU/ml are considered positive.
This protection declined significantly over the next ten weeks, dropping to 115.7 BAU/ml. After the boost, however, the IgG concentration rose again, growing 25-fold and reaching 2843 BAU/ml. Regarding the levels of neutralizing antibodies, there was an increase from 23.5% between the second dose and 99.3% after the booster.
Among those immunized with Astrazeneca vaccine and the third dose of Pfizer, median IgG responses increased from 86.8 BAU/ml to 648.9 BAU/ml during the first two applications. Then they dropped to 390.9 BAU/ml. But with the booster, they went up sevenfold – to 2,799.2 BAU/ml. The levels of neutralizing antibodies increased from 63.2% to 98.9%.
“It is possible to see that even with the reduction of immunity in the period after the second dose, there is still a relevant cellular response against the coronavirus antigens. However, the interesting thing is that, after the third dose, both groups had a significant increase in both the response cell phone like humoral [de anticorpos]. This was something that impressed us, indicating a good response in both groups”, explains Tashima.
One of the limitations of the study was the fact that it was not possible to compare the results with data from the general population or specific groups, such as the elderly.
Some volunteers who participated in the study were contaminated by the variant omicron after booster vaccination. The researchers are now in a new stage of collecting blood from these people to analyze possible impacts of the variant, which in early January accounted for 97% of Covid-19 cases in Brazil.