China's SinoVac Vaccine Shows 'No Detectable Neutralization' Against Omicron Variant: Study

A two-dose regimen of China’s Sinovac COVID-19 vaccine, CoronaVac, may not be enough to protect recipients against the highly transmissible and heavily mutated Omicron variant, a new study has found.

The study, conducted by researchers from Yale University, the Dominican Republic’s Ministry of Health and other institutions, found that two doses of the Sinovac vaccine alone did not show any detectable neutralization against the B.1.1.529 variant. The data was based on plasma samples from 101 participants who received the China-made vaccine in the Dominican Republic.

“In CoronaVac fully vaccinated (2x) people, there was NO detectable neutralization against the infectious Omicron virus. Antibodies were assayed at mean days from second Coronavac shot of 113 days,” Prof. Akiko Iwasaki, one of the study’s authors, said on Twitter.

The study also found that two doses of the Sinovac vaccine along with one booster shot of the Pfizer vaccine only produced antibody levels similar to those produced by a two-dose regimen of an mRNA vaccine.

Antibody levels of those who received two doses of CoronaVac and one dose of the Pfizer vaccine were 6.3-fold lower against Omicron when compared with the original strain and 2.7-fold lower when compared with the Delta variant.

Prof. Iwasaki said Sinovac recipients may need to get two booster doses to achieve antibody levels needed to fight against the Omicron variant.

“In terms of public health, CoronaVac 2x is insufficient to neutralize Omicron. Even with CoronaVac 2x plus Pfizer booster, NAb is only 1.4x higher than 2x mRNA alone. Thus, CoronaVac recipients may need 2 additional booster doses to reach levels needed against Omicron,” she wrote in a tweet.

The study comes after research published last week by researchers from the University of Hong Kong said that none of the samples from 25 CoronaVac vaccine recipients showed any detectable antibodies that neutralized the Omicron variant.

The study also found that people who received only two doses of the Pfizer-BioNTech vaccine only had 24% of detectable neutralizing antibodies against the highly transmissible COVID-19 variant.

A spokesperson for Sinovac later cited its own laboratory testing that showed a booster dose of its vaccine was 94% effective against the Omicron variant.