RIO DE JANEIRO, BRAZIL – A study conducted in Hong Kong found that individuals vaccinated with Pfizer-BioNTech’s coronavirus immunizer have 10 times more antibodies than those vaccinated with Sinovac, and that the latter produce “similar or lower” levels of virus-targeting proteins than naturally produced in recovered Covid-19 patients.
The University of Hong Kong findings, published Friday in the scientific journal Lancet Microbe, may suggest the need for “alternative strategies” – including booster vaccines – to enhance antibody levels in Sinovac-immunized individuals and protection against Covid-19 disease, according to the researchers.
The presence of antibodies is an indication of a previous infection, or that a vaccine is working to protect an individual, but the amount of proteins produced by the body to identify and neutralize the coronavirus does not directly correlate with the level of immunity.
However, according to experts, there is growing evidence that higher levels often correlate with stronger and longer-lasting protection against infection.
In their study, epidemiologists Benjamin Cowling and Gabriel Leung, and virologist Malik Peiris said that the difference in neutralizing antibody levels identified in the study “could translate into substantial differences in vaccine efficacy.”
Cowling noted that moderate levels of protection were still better than nothing, which is why he urged the Hong Kong population to be vaccinated.
As of Thursday, Hong Kong had administered over 4.5 million coronavirus vaccine doses, of which 2.6 million were from Pfizer-BioNTech and 1.8 million from China’s Sinovac.
For the antibody study, researchers tested 1,442 healthcare workers from public and private hospitals and clinics in the city, taking blood samples at different intervals.
In the first batch of 93 fully vaccinated participants, the antibody levels of the 63 Pfizer-BioNTech recipients increased “substantially” after the first dose and again after the second dose. In contrast, the 30 Sinovac recipients had “low” antibody levels after their first shot, and “moderate” after the second.
The researchers found that the average antibody levels of a subset of 12 Pfizer-BioNTech recipients were 10 times higher (269) than those of an equal number of individuals in the Sinovac group, who averaged 27.
The scientists also found that the Pfizer-BioNTech vaccinee with the lowest level of antibodies still had more than the Sinovac vaccinee with the highest number of antibodies. The antibody levels produced by Sinovac were found to be equal to or slightly lower than those detected in Covid-19-recovered individuals.
Cowling said the difference between the two drugs was consistent with what was reported by the manufacturers in their Phase III clinical trials, which found Pfizer-BioNTech to be 95% effective, compared with 50.7% for Sinovac.
The results suggest a potential need for Sinovac recipients – especially the elderly who have a weaker immune response to vaccines – to be administered a third booster dose, Cowling said.
Source: Infobae