Although Sinovac vaccine is less effective for mild cases of Covid, it is 100% effective for severe cases

New test results for the Chinese Sinovac Covid-19 vaccine show that it is 100% effective against severe cases, including hospitalizations and death, of the virus despite being less effective than other vaccines against milder cases.

A late-stage trial in Brazil, concluded two weeks ago, indicated that Sinovac is only 50.7 percent effective against all cases of Covid but that the effectiveness increases dramatically as severity increases. Sinovac’s Brazilian partner, Butantan, reported its results in a preprint paper posted Sunday, confirming results announced earlier.

Based on results of the Brazilian and other recent data, the World Health Organization says it recommends Sinovac for general use although it adds that testing currently underway will present “a more complete picture” of the vaccine’s effectiveness.

Butantan said that more trials with more participants are needed to gauge long-term results. The authors noted higher efficacy with more time between doses — 21 days rather than 14 — but didn’t provide exact figures. Butantan tested the vaccine in more than 12,000 health workers across 16 sites in Brazil.

The report said the vaccine was generally well tolerated. Some people had pain at the injection site and muscle aches. The report also reported high efficacy against the current variants of the virus, including one in Brazil.

Another test in Turkey, conducted in February and March, found Sinovac much more effective overall, 83.5 percent, but researchers said the trials were too small to provide definitive results

Despite the positive results in Brazil and Turkey, George Fu Gao, head of the Chinese Center for Disease Prevention and Control, said Saturday that the vaccine wasn’t as good as expected and said that CoronaVac, the maker of Sinovac, is considering options, including booster shots and combinations with other vaccines to strengthen protecting against milder cases.

The Brazilian study included people over 60 — about 15 percent of participants — and took place in a country where coronavirus cases are surging.

Sinovac is being distributed worldwide, with more than 20 million doses administered. In Latin America, it is being used in Ecuador, Chile, Brazil, Paraguay, Uruguay and Mexico.

Brazil has more than 330 new cases per million every day, compared with 206 in the US and 22 in the UK, according to Oxford University’s Our World in Data.