The Covid-19 vaccine Sinovac, two-dose, followed by a Pfizer-BioNTech booster injection, showed a lower immune response against the variant Omicron compared to other mutations, according to a study by researchers.
The study, which has not yet been peer-reviewed, was conducted by researchers from Yale University, the Dominican Republic’s Ministry of Health, and other institutions.
The two-dose Sinovac regimen in conjunction with the Pfizer injection produced an antibody response similar to that of a two-dose mRNA vaccine, according to the study.
Antibody levels against Omicron were 6.3 times smaller compared to the original variant and 2.7 times smaller compared to delta.
Akiko Iwasaki, one of the study’s authors, said on Twitter that CoronaVac recipients may need two additional booster doses to reach the necessary levels of protection against Omicron.
The two-dose Sinovac vaccine alone did not show any detectable neutralization against Omicron, according to the study that analyzed plasma samples from 101 participants in the Dominican Republic.
A study conducted last week in Hong Kong noted that even three doses of the Sinovac vaccine did not produce a sufficient antibody response against Omicron and had to be boosted with an injection of Pfizer-BioNTech to achieve “levels of protection.”
The CoronaVac vaccine from Sinovac and the BBIBP-CorV vaccine from the state-owned company Sinopharm are the two most widely used vaccines in China and the main Covid-19 injections exported by the country. Hong Kong has been using vaccines from Sinovac and Pfizer-BioNTech.