Sao Paulo: A leading Chinese Covid-19 vaccine, developed by Sinovac Biotech, has been found to be 50.4 per cent effective in Brazilian clinical trials, researchers have found.
According to the latest results released by researchers, it shows the vaccine is significantly less effective than previous data suggested -- barely over the 50 per cent needed for regulatory approval.
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, BBC reported on Thursday.
Last week, researchers at the Butantan Institute, which has been conducting the trials in Brazil, announced that the vaccine had a 78 per cent efficacy against "mild-to-severe" Covid-19 cases.
But, on Tuesday, they revealed that calculations for this figure did not include data from a group of "very mild infections" among those who received the vaccine that did not require clinical assistance.
With the inclusion of this data, the efficacy rate is now 50.4 per cent, said researchers.
But, the researchers stressed that the vaccine is 78 per cent effective in preventing mild cases that needed treatment and 100 per cent effective in staving off moderate to serious cases.
The Sinovac trials have yielded different results across different countries.
Last month, Turkish researchers said the Sinovac vaccine was 91.25 per cent effective, while Indonesia, which rolled out its mass vaccination programme on Wednesday, said it was 65.3 per cent effective. Both were interim results from late-stage trials.
A figure for efficacy is reached by looking at how many people developed Covid after being given the vaccine, compared with how many were affected when given a dummy injection. Normally, that is based on people developing obvious symptoms but in this Brazilian trial, people with no symptoms also appear to have been included.
Brazil has been one of the countries worst affected by Covid-19.