Sinovac Biotech’s experimental COVID-19 vaccine CoronaVac triggered a quick immune response but the level of antibodies produced was lower than in people who had recovered from the disease, preliminary trial results showed on Wednesday.

While the early to mid-stage trials were not designed to assess the efficacy of CoronaVac, researchers said it could provide sufficient protection, based on their experience with other vaccines and data from preclinical studies with macaques.

The study comes hot on the heels of upbeat news this month from U.S. drugmakers Pfizer and Moderna as well as Russia that showed their experimental vaccines were over 90% effective based on interim data from large, late-stage trials.

CoronaVac and four other experimental vaccines developed in China are currently undergoing late-stage trials to determine their effectiveness in preventing COVID-19.

The Sinovac findings, published in a peer-reviewed paper in medical journal The Lancet Infectious Diseases, came from results in Phase I and Phase II clinical trials in China involving more than 700 participants.

“Our findings show that CoronaVac is capable of inducing a quick antibody response within four weeks of immunisation by giving two doses of the vaccine at a 14-day interval,” Zhu Fengcai, one of the authors of the paper, said.

“We believe that this makes the vaccine suitable for emergency use during the pandemic,” Zhu said in a statement published alongside the paper.

Researchers said the findings from large, late-stage studies, or Phase III trials, would be crucial to determine if the immune response generated by CoronaVac was sufficient to protect people from the coronavirus infection.

Sinovac is currently running three Phase III trials in Indonesia, Brazil and Turkey.

The results must be interpreted with caution until Phase III results are published, Naor Bar-Zeev, a professor from Johns Hopkins University who was not involved in the study, said.

“But even then, after Phase III trial completion and after licensure, we should prudently remain cautious,” he said. (Reuters)