China’s Sinovac Biotech has said a clinical trial in Brazil showed its Covid-19 vaccine was almost 20 per cent more effective in a small sub-group of patients who received their two doses longer apart.

The protection rate for 1,394 participants who received doses of either CoronaVac or a placebo three weeks apart was nearly 70pc, a Sinovac spokesman said. The spokesman said a small number of participants received their second shot late due to various reasons, without elaborating on them.

While Sinovac’s researchers had said early-stage trials showed a four-week interval induced the stronger antibody response than two weeks, this is the first time the company has released efficacy data from a Phase III trial with dosing patterns that differ from its trial protocol.