Chinese Covid-19 vaccine also found safe, induces immune response

Results from an early-phase randomised clinical trial of a Chinese vaccine candidate based on the inactivated whole SARS-CoV-2 virus (CoronaVac) show that the formulation appears safe and induces an antibody response in health volunteers aged 18 to 59 years.

The results, published on Tuesday in The Lancet Infectious Diseases Journal, add to the number of vaccine candidates under trial that have been found safe. The Chinese trial involved more than 700 volunteers recruited in China between April 16 and May 5.

“The vaccine appeared to be safe and well tolerated at all tested doses. The most common reported side effect was pain at the injection site. Within 14 days of the final dose, study detected robust antibody responses after two injections of the vaccine candidate were given 14 days apart, even at lowest dose tested (3µg)”, the journal said.

The results showed that antibody levels induced by the vaccine were lower than those seen in people who have been infected by and recovered from Covid-19, but researchers said they still expect the vaccine could provide protection from the virus.

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Antibody responses could be induced within 28 days of the first immunisation by giving two doses of the vaccine candidate 14 days apart, the results showed. The study also identified the optimum dose to generate the highest antibody responses, while taking account of side effects and production capacity: 3µg.

Fengcai Zhu, joint lead author of the study, from the Jiangsu Provincial Center for Disease Control and Prevention, Nanjing, China, said: “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”.

“We believe that this makes the vaccine suitable for emergency use during the pandemic. In the longer term, when the risk of Covid-19 is lower, our findings suggest that giving two doses with a one month interval, rather than a two week interval, might be more appropriate for inducing stronger and potentially longer-lasting immune responses. However, further studies are needed to check how long the antibody response remains after either vaccination schedule.”

CoronaVac is a chemically-inactivated whole virus vaccine based on a strain of SARS-CoV-2 that was originally isolated from a patient in China. The phase 1/2 clinical trial was carried out in the Suining County of Jiangsu province in China.

Writing in a linked Comment, Naor Bar-Zeev from Johns Hopkins University, who was not involved in the study, said: “Like all phase 2 trials, the results must be interpreted with caution until phase 3 results are published. But even then, after phase 3 trial completion and after licensure, we should prudently remain cautious.”