In Brazil Study, Sinovac’s COVID-19 Vaccine is Just 50 Percent Effective

Brazil’s Butantan Institute has reported that Sinovac’s COVID-19 vaccine, CoronaVac, demonstrated an overall efficacy of only 50.38 percent in a phase 3 trial, putting it barely over the World Health Organization’s 50 percent efficacy threshold for approval.

The late-stage trial included 12,500 volunteers, all healthcare workers, across 16 sites in the country. The researchers previously said that the vaccine offered 78 percent efficacy against mild-to-severe infections, but they failed to include data from volunteers who contracted mild cases.

Brazil’s drug regulator, the National Health Surveillance Agency, said it is now reviewing the data for a possible emergency-use approval. But vaccine experts have concerns about the data’s reliability because of varying efficacy rates reported by different countries and a lack of transparency by Sinovac.