BEIJING (Reuters) – A Chinese company, Sinovac Biotech, said on Monday that a clinical trial in Brazil showed that the COVID-19 vaccine was about 20 percentage points more effective in a small subset of patients who received the two longer doses.
A Sinovac spokesperson said the protection rate for 1,394 participants who received doses of CoronaVac or placebo three weeks apart from each other was roughly 70%.
Brazilian researchers announced last week that the vaccine’s overall effectiveness was 50.4% based on results from more than 9,000 volunteers, most of whom received doses 14 days apart, as shown in the trial protocol.
The spokesman said a small number of participants received a second shot late for various reasons, without going into details.
The dosing interval of COVID-19 vaccines has become a hot topic of debate among scientists, regulators and governments.
Regulators in the UK said the COVID-19 vaccine from AstraZeneca and the University of Oxford is most effective when there is a larger gap between doses than was initially envisioned.
Britain has also decided to allow a longer gap between the COVID-19 vaccine doses from Pfizer and BioNTech, although the companies say they only have efficacy data for a shorter period between shots.
A Sinovac spokesperson cautioned that the robustness of the data from the subgroup was weaker than the 50% score, which is based on pooled data for those receiving two or three-week doses.
While the Sinovac researchers said early-stage trials showed that a four-week break caused a stronger antibody response over two weeks, this is the first time the company has released efficacy data from a Phase 3 trial with dosage patterns that differ from its experimental protocol.
Sinovac has not yet released the global results of its Phase 3 trials, but the COVID-19 vaccine has been approved for use in emergency situations in many countries, including Brazil, Indonesia and Turkey.
(Prepared by Roxanne Liu and Ryan Wu. Editing by Mark Potter)