A leading Covid-19 vaccine under development in China showed inconclusive results about its level of protection, although scientists remain optimistic that the candidate can be among a roster of effective vaccines used to fight the pandemic.
In early-stage clinical trials, Sinovac Biotech Ltd.’s CoronaVac vaccine was shown to induce antibodies in the human body within 28 days of the first immunization, according to results published in the Lancet medical journal this week. The level of antibodies, however, were lower than that seen in people who were previously infected with Covid-19.
By contrast, the levels of antibodies in results from vaccine trials by Pfizer Inc. and Moderna Inc. were roughly on par with those in people who previously contracted the virus. This week, Pfizer said its experimental vaccine was 95% effective at protecting people from Covid-19, while Moderna said its vaccine was 94.5% effective based on an early look at late-stage results.
The results from Sinovac are for Phase 1 and Phase 2 clinical trials, which aren’t designed to measure whether the vaccine works but can indicate whether it provokes an appropriate immune response. The firm hasn’t published late-stage, or Phase 3, results, which measure efficacy.
“One would have liked the antibody levels to be comparable,” said William Schaffner, professor of preventive medicine at Vanderbilt University School of Medicine. However, he said, the finding “may just mean the duration of protection may not be quite as long.”