Brazil researchers report more modest 50.4% efficacy for China's CoronaVac

A coronavirus vaccine developed by China's Sinovac showed "general efficacy" of 50.4% in a late-stage trial in Brazil, the company's local partners said on Tuesday, revealing a more modest figure after pressure for more transparency.

On Thursday, the Brazilian researchers had celebrated results showing 78% efficacy against mild COVID-19 cases, a rate they have since described as "clinical efficacy." Ricardo Palacios, medical director for clinical research at the Butantan biomedical center in Sao Paulo, said the new figure included infections classified as "very mild" because they did not require clinical assistance.

Piecemeal disclosure from global studies of the vaccine, called CoronaVac, have added to concerns that immunizations developed by Chinese producers are not subject to the same public scrutiny as U.S. and European alternatives. Researchers at Butantan delayed the announcement of their results three times, blaming a confidentiality clause in a contract with Sinovac.

Turkish researchers said last month that CoronaVac was 91.25% effective based on an interim analysis. Indonesia gave the vaccine emergency use approval on Monday based on interim data showing it is 65% effective. Butantan officials said the design of the Brazilian study, focusing on frontline health workers during a severe outbreak in Brazil and including elderly volunteers, made it impossible to compare the results directly with other trials or vaccines.