Dec 31 (Reuters) - Sinovac's two-dose COVID-19 vaccine followed by a booster Pfizer-BioNTech shot showed a lower immune response against the Omicron variant compared with other strains, according to a study by researchers.
The study, which has not been peer-reviewed yet, was conducted by researchers from Yale University, the Dominican Republic's Ministry of Health and other institutions.
The Sinovac (SVA.O) two-dose regimen along with the Pfizer (PFE.N) shot produced an antibody response similar to a two-dose mRNA vaccine, according to the study. Antibody levels against Omicron were 6.3-fold lower when compared with the ancestral variant and 2.7-fold lower when compared with Delta.
Akiko Iwasaki, one of the authors of the study, said on Twitter that CoronaVac recipients may need two additional booster doses to achieve protective levels needed against Omicron.
The two-dose Sinovac vaccine alone did not show any detectable neutralization against Omicron, according to the study that analysed plasma samples from 101 participants in the Dominican Republic.
A study from Hong Kong last week said that even three doses of the Sinovac vaccine did not produce enough antibody response against Omicron and that it had to be boosted by a Pfizer-BioNTech shot to achieve "protective levels."
https://www.reuters.com/world/china/chinas-sinovac-covid-19-booster-weaker-against-omicron-hong-kong-study-2021-12-23/
Dec 23 (Reuters) - Three doses of Sinovac's CoronaVac COVID-19 vaccine do not produce adequate levels of antibodies to fight the Omicron variant of the coronavirus, researchers from Hong Kong said in a statement.
Their analysis revealed Pfizer-BioNTech vaccine was more effective, as a third dose of the shot administered after two doses of the same or China's Sinovac vaccine provided "protective levels" of antibody against Omicron.
Pfizer (PFE.N) and its German partner BioNTech have said their three-shot course was able to neutralise the new Omicron variant in a laboratory test.
The latest study was conducted by researchers from the University of Hong Kong and the Chinese University of Hong Kong, and funded by the Health and Medical Research Fund and the Government of Hong Kong.
The statement did not say how many samples were used in the analysis. Sinovac did not immediately respond to a request for comment.
Sinovac's CoronaVac and state-owned Sinopharm's BBIBP-CorV vaccine are the two most-used vaccines in China and the leading COVID-19 vaccines exported by the country. Sinopharm also has a second vaccine in use in China.
Hong Kong has been using the Sinovac and Pfizer-BioNTech shots. But people aged 12-17 are eligible only for the BioNTech vaccine.
Referencei
- Immunogenicity of heterologous BNT162b2 booster in fully vaccinated individuals with CoronaVac against SARS-CoV-2 variants Delta and Omicron: the Dominican Republic Experience https://www.medrxiv.org/content/10.1101/2021.12.27.21268459v1
- Statement from Akiko Iwasaki, PhD
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