The CoronaVac vaccine reduces coronavirus mortality by 97 per cent, according to early results of the immunisation campaign in Uruguay, which relies heavily on the Chinese jab.
In people who had received two doses, it reduced infection with the coronavirus by 57 per cent and intensive care admissions by 95 per cent, said a report by the health ministry of the South American nation.
Compared to other vaccines in use, there have been few scientific publications on the efficacy of CoronaVac, produced by Chinese firm Sinovac, and widely divergent reported results.
Coronavac is nevertheless widely used in China and in some two dozen other countries including Pakistan.
Chile reported last month that early results from its immunisation campaign showed CoronaVac to be 67 per cent effective at preventing symptomatic Covid-19 and 80 per cent at preventing death.
Trial results with CoronaVac in Brazil showed efficacy of about 50 per cent in preventing symptomatic infection, while Turkish data said it was more than 80 per cent effective.
Uruguay, which started vaccinating on March 1, has used CoronaVac in more than 80 per cent of cases.
It has reserved the Pfizer-BioNTech jab for older people, health workers, and people other illnesses.
The results are based on outcomes two weeks after administering two shots to some 862,000 people — more than 712,000 who received CoronaVac and almost 150,000 Pfizer.
The Pfizer shot, the results showed, was 75 per cent effective at preventing infection, 99 percent effective at preventing illness requiring ICU admission, and 80 per cent effective at preventing death.
The results with the two vaccines are not directly comparable, as recipients of Pfizer in Uruguay fell into higher-risk categories, the ministry said.
Other studies have attached much better outcomes to Pfizer.
The largest real-world Pfizer study yet, in Israel, said this month it provided more than 95 per cent protection against Covid-19.
CoronaVac is a traditional type of vaccine, using inactivated virus to trigger immunity, while Pfizer uses RNA messenger technology.
The ministry said the results are preliminary and should be interpreted with caution, as some data has yet to be processed.