BEIJING (Reuters) – Chinese Sinovac Biotech said on Monday that a clinical trial in Brazil showed that the COVID-19 vaccine was nearly 20 percentage points more effective in a small subgroup of patients receiving two doses longer.
The protection rate for 1,394 participants who received doses of 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 the results of more than 9,000 volunteers, most of whom received doses 14 days apart, as set out in the trial protocol.
The spokesperson said that a small number of participants had their second shot received for various reasons, without expanding it.
The dosing interval for COVID-19 vaccines has become an extremely important topic for scientists, regulators and governments.
UK regulators have said a COVID-19 vaccine from AstraZeneca and Oxford University is more effective if there is a longer dose gap than originally planned.
Britain has also decided to allow a longer dose gap between a Pvizer and BioNTech COVID-19 vaccine, although the companies say they only have efficacy data for a shorter period between shots.
The Sinovac spokesperson warned that the robustness of the data from the subgroup is weaker than the 50% result, which is based on the combined data of those who received doses two to three weeks apart.
While Sinovac researchers said that early-stage tests show that an interval of four weeks elicits the stronger antibody response than two weeks, this is the first time the company has released efficacy data from a phase III study with dosing patterns that differ from the trial protocol.
Sinovac has not yet announced worldwide results of its Phase III trials, but the COVID-19 vaccine has been approved for emergency use in several countries, including Brazil, Indonesia and Turkey.
(Reporting by Roxanne Liu and Ryan Woo. Edited by Mark Potter)