The COVID-19 vaccine developed by China's Sinovac Biotech is effective against the UK and South African variants, the vaccine's Brazilian partner said on Wednesday, citing test results in Chinese trials.

"We have tested this vaccine in China against the English and the South African variants, with good results," said Dimas Covas, head of the Butantan biomedical center in Sao Paulo, which leads domestic trials of the Chinese vaccine and is supplying doses to Brazil's Health Ministry.

Covas did not give any more details on exactly how effective the vaccine proved against these strains.

Butantan is also testing the vaccine, known as CoronaVac, against the Brazilian variant of the virus which appeared in the city of Manaus, he said.

"Soon we will have the results and we are very positive it will do the job," Covas said.

Covas was speaking at a news conference in the small city of Serrana, in the interior of Sao Paulo state, where Butantan began a mass vaccination campaign on Wednesday aimed at inoculating the entire adult population against COVID-19 to test whether it lowers the infection rate.