 China-based Sinovac Biotech Ltds NASDAQ: SVA two-dose COVID-19 vaccine followed by a booster Pfizer Inc NYSE: PFE -BioNTech SE NASDAQ: BNTX shot showed a lower immune response against the Omicron variant compared with other strains, according to a study. The study was conducted by researchers from Yale University, the Dominican Republics Ministry of Health, and other institutions. 