Leading Chinese vaccine induces ‘robust’ immune response against coronavirus, study shows

Sinovac’s candidate appears to be safe and well-tolerated, with further analysis ongoing to determine its efficacy levels

A leading coronavirus vaccine developed by the Chinese pharmaceutical firm Sinovac has shown to be capable of triggering a “robust” immune response in healthy people, according to a preliminary study.

The candidate, called CoronaVac, appears to be safe and well-tolerated, researchers said, adding that the most common reported side effect was pain at the injection site.

Antibody levels induced by the vaccine were lower than those seen in people who have been infected by and recovered from Covid-19, but scientists believe it will still be able to provide protection from the virus.

The new findings come from a phase-two trial that involved more than 700 healthy volunteers aged 18-59 years recruited in China between 16 April and 5 May.

Participants received two doses of the CoronaVac candidate 14 days apart, with a “robust antibody response” detected within two weeks of the final injection.

The primary objective of the trial was to evaluate the immune response and safety of the vaccine – not to assess how effective it is at preventing infection.

This will be determined in Sinovac’s ongoing large-scale trials, which have enrolled more than 24,000 people across Brazil, Bangladesh, Turkey and Indonesia.

CoronaVac is considered a global frontrunner in the race to develop a protective shot against Sars-CoV-2 – the virus that causes Covid-19. It is one of 12 experimental vaccines that are currently in the phase-three trials.

In September, Sinovac said that its vaccine would be ready by early 2021 for distribution worldwide.

The company is developing one of China’s top four vaccine candidates along with state-owned Sinopharm, which has two in development, and military-affiliated private firm CanSino.

Addressing the latest findings from the phase-two trial, professor Fengcai Zhu, joint lead author of the study, 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.”

He said the persistence of the antibody response needs to be verified in future studies to determine how long-lived any protection might be.

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-two trial was carried out in the Suining County of Jiangsu province, China.

All participants did not have any history of infection with Covid-19, had not travelled to areas with high incidence of the disease, and did not have signs of fever at the time of recruitment.

The latest findings have been peer-reviewed and published in The Lancet Infectious Diseases journal.

They follow announcements made by Moderna and Pfizer that their mRNA-based vaccines are more than 90 per cent effective in preventing Covid-19, according to provisional phase-three data. The two companies are expected to start delivering doses next month.

Sinovac chief executive Yin Weidong, who has personally been given the experimental vaccine, said in September that he was confident that CoronaVac would meet the regulatory standards of the US and European Union. “Our goal is to provide the vaccine to the world,” he said.

Earlier this month, the company’s phase-three trial was temporarily paused after a “serious adverse event” in one of the volunteers was reported.

President Jair Bolsonaro, who has been critical of China and spoken dismissively of CoronaVac, sparked a political firestorm after calling the suspension a political victory.

Local reports later claimed that the volunteer in question had died by suicide.

Brazil’s National Health Surveillance Agency said last week that clinical trials would be allowed to restart following the conclusion of a risk assessment.