Results of a Brazilian trial show that the Covid-19 vaccine developed by China’s Sinovac Biotech is just 50.4% effective.
This means that it barely meets the threshold for regulatory approval and is well below the initially reported efficacy rate, according to several media reports.
Brazil, with just over eight million infections and more than 200,000 deaths, is the first country to complete a late-stage trial of the vaccine CoronaVac.
The state-run Butantan Institute in Sao Paulo has been criticised for a lack of transparency in making public its trial data. It reportedly delayed the release of trial results three times, blaming a confidentially clause in its contract with China.
The institute, which is the largest vaccine producer in Latin America and one of the largest in the world, announced last week that CoronaVac was 78% effective, but then on Tuesday said that the overall efficacy rate had fallen to 50.4%, reported the Wall Street Journal
In comparison, Covid vaccines from Pfizer-BioNTech and Moderna were found to be about 95% effective in their late-stage trials.
Brazil and other developing nations have pinned their hopes on Chinese vaccines as wealthier countries snap up vaccines developed in the West.
Sinovac’s vaccine is also cheaper and easier to transport because it can be stored in ordinary refrigerators unlike the vaccines from Pfizer-BioNTech and Moderna that must be kept at subfreezing temperatures.
Butantan has requested for CoronaVac to be authorized for emergency use in Brazil, reports Reuters.
The country’s health regulator Anvisa, which has stipulated a minimum 50% efficacy rate for vaccines to be approved, said it will meet on Sunday to decide.
As well as Brazil, other developing countries including Turkey and Indonesia are also conducting CoronaVac trials.
Indonesia on Monday approved the vaccine for emergency use, making it the first country outside China to do so after interim data from a late-stage trial showed that CoronaVac was 65.3% effective, reported Reuters.
Meanwhile, Turkish researchers said their interim analysis showed the vaccine to be 91.25% effective, Reuters reported last month.