Covid-19 vaccine more effective with longer dose interval, says China's Sinovac

China's Sinovac Biotech said on Monday that a clinical trial in Brazil showed its Covid-19 vaccine was almost 20 percentage points 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 placebo three weeks apart was nearly 70%, a Sinovac spokesman said.

Brazilian researchers announced last week that the vaccine's overall efficacy was 50.4% based on results from more than 9,000 volunteers, most of whom received doses 14 days apart, as outlined in the trial protocol.

Read | What's behind varying efficacy data for Sinovac's Covid-19 vaccine?

The spokesman said a small number of participants received their second shot late due to various reasons, without elaborating.

The dosing interval for Covid-19 vaccines has become a hot topic of debate among scientists, regulators and governments.

UK regulators have said a Covid-19 vaccine from AstraZeneca and Oxford University is more effective when there is a longer gap between doses than initially envisaged.

Britain has also decided to allow a longer gap between doses of a Covid-19 vaccine from Pfizer and BioNTech, even though the companies say they only have efficacy data for a shorter period between shots.

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The Sinovac spokesman cautioned the robustness of the data from the sub-group was weaker than the 50% result, which is based on the combined data of those receiving doses two or three weeks apart.

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.

Sinovac has yet to release global results of its Phase III trials, but its Covid-19 vaccine has been approved for emergency use in several countries, including Brazil, Indonesia and Turkey.