The safety and efficacy of Chinese vaccine is being widely recognized by various countries," Chinese Foreign Minister Wang Yi said at a news conference in March.

The relatively low efficacy rate of Chinese vaccines, however, could hamper credibility and dent Beijing's so-called vaccine diplomacy.

The two pharmaceutical firms that supply the majority of Chinese Covid-19 vaccines to the world have not published comprehensive clinical trial data in medical journals on their vaccines' effectiveness.

But from the interim results announced by the companies, their efficacy falls far behind the new type of vaccines developed in the West that use mRNA to trigger an immune response.

The CoronaVac vaccine developed by Sinovac, a private company, was found to have an efficacy rate of just 50.4% in clinical trials in Brazil.

Another trial in Turkey showed it was 83.5% effective.