In a study published on May 26 in JAMA, Sinopharm researchers reported results suggesting that their inactivated virus vaccine was up to 78 percent effective against symptomatic COVID-19 cases. But the study was done mainly in young, healthy men, and the results were not conclusive regarding whether the vaccine was effective against severe disease or asymptomatic cases. Unpublished data out of Serbia suggested that some people given the vaccine may not produce antibodies to fight off the pandemic coronavirus three months after vaccination, according to reporting by the Wall Street Journal. “The Sinopharm vaccine is not immunogenic enough, and it appears that its impact is especially low on elderly recipients,” said Olgica Djurkovic-Djakovic, of the University of Belgrade, who led the unpublished study and shared the findings with the Journal.