BEIJING/NEW YORK • Sinovac Biotech's experimental Covid-19 vaccine 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 yesterday.
While the early to mid-stage trials were not designed to assess the efficacy of the vaccine, known as CoronaVac, researchers said it could provide sufficient protection, based on their experience with other vaccines and data from pre-clinical studies with macaques.
The study comes hot on the heels of upbeat news this month from United States drugmakers Pfizer and Moderna that showed their experimental vaccines were over 90 per cent effective, based on interim data from large, late-stage trials.
CoronaVac and four other experimental vaccines developed in China are 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 one and phase two 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," said Professor Zhu Fengcai, one of the authors of the paper.
"We believe that this makes the vaccine suitable for emergency use during the pandemic," Prof Zhu said in a statement published alongside the paper.
Researchers said the findings from large, late-stage studies, or phase three 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 three trials - in Indonesia, Brazil and Turkey.
Dr Naor Bar-Zeev from Johns Hopkins University, who was not involved in the study, said the results must be interpreted with caution until phase three results are published. "But even then, after phase three trial completion and after licensure, we should prudently remain cautious," he said.
CoronaVac is one of three experimental Covid-19 vaccines that China has been using to inoculate hundreds of thousands of people under an emergency-use programme. The other two are developed by institutes linked to Chinese pharmaceutical company Sinopharm.
The Sinopharm vaccines, as well as another one from CanSino Biologics, were also shown to be safe and triggered immune responses in early and mid-stage trials, according to peer-reviewed papers.
Dr Gang Zeng, a Sinovac researcher involved in the CoronaVac study, said the vaccine could be an attractive option as it can be stored at normal fridge temperatures of 2 deg C to 8 deg C and may remain stable for up to three years. "(It) would offer some advantages for distribution to regions where access to refrigeration is challenging," he said.
Another promising vaccine candidate being developed by French drugmaker Sanofi would not need to be super-cooled either.
In contrast, vaccines developed by Pfizer/BioNTech and Moderna use a new technology called synthetic messenger RNA to activate the immune system against the virus and require far colder storage.
Pfizer's vaccine must be stored and transported at minus 70 deg C, though it can be kept in a normal fridge for up to five days, or up to 15 days in a thermal shipping box. Moderna's vaccine is expected to be stable at normal fridge temperatures for 30 days but for storage of up to six months, it needs to be kept at minus 20 deg C.
Separately, Pfizer's chief executive Albert Bourla said on Tuesday that the firm plans to submit its vaccine data to the US Food and Drug Administration for emergency-use authorisation.