Researchers in Brazil say a coronavirus vaccine developed by China’s Sinovac has been found to be just 50.4% effective.
It shows the vaccine is significantly less effective than previous data suggested.
The Chinese vaccine is one of two that the Brazilian government has lined up for its citizens.
Brazil has been one of the countries worst affected by Covid-19.
Sinovac, a Beijing-based biopharmaceutical company, is behind CoronaVac, an inactivated vaccine.
It works by using killed viral particles to expose the body’s immune system to the virus without risking a serious disease response.
Several countries, including Indonesia, Turkey and Singapore, have placed orders for the vaccine.