People who were originally fully vaccinated with the Chinese-made Sinovac COVID-19 vaccine were shown to develop a high degree of immunity after receiving booster doses of either AstraZeneca, Pfizer or Johnson & Johnson vaccines.
In the Brazilian government-funded phase 4 study conducted by researchers from Brazil and Oxford University, patients who received an initial vaccination from Sinovac shots were found to develop significantly higher immune responses when given a booster shot from another vaccine manufacturer. The study found, however, that those who received a Sinovac booster also had a signifcantly stronger immune response.
There was concern in several Latin American countries in December when two studies indicated people vaccinated with Sinovac had less immune resistance to the Omicron variant than those vaccinated with other vaccines. Sinovac has been widely administered in Ecuador, Chile, Brazil and other countries in the region.
Researchers noted only around a fifth of participants aged 18-60 and less than 10 percent of those over the age of 60 had detectable levels of antibodies when the study began. In all observations, the three vaccines that came from companies other than Sinovac were found to induce a greater immune response.
According to researchers, mixed vaccine doses were shown to induce antibodies at “8–22-fold higher” than when older adult patients were given another Sinovac dose. They also found that administering vaccines other than Sinovac’s increased immunity against both the omicron and delta variants.
The study observed over 1,200 participants in Brazil who had received the Sinovac vaccine around six months before the study. Participants were randomly chosen to receive one of the four vaccines that were used.
“This study shows that the inactivated vaccine, CoronaVac, can be successfully boosted with a range of different vaccines, with the strongest responses when a viral vector or RNA vaccine is used,” Sir Andrew Pollard, director of the Oxford Vaccine Group said.
“The global priority remains first and second doses but this study provides important options for policymakers in the many countries where inactivated vaccines, like CoronaVac, have been used.”
Credit: The Hill