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A leading Covid-19 vaccine under development in China has shown inconclusive results on its level of protection, although scientists remain optimistic the candidate may be on a list of effective vaccines in use to fight the pandemic.
In early clinical trials, the CoronaVac vaccine from Sinovac Biotech Ltd. has been shown to induce antibodies in the human body within 28 days of the first immunization, according to results published this week in the Lancet medical journal. The level of antibodies, however, was lower than seen in people previously infected with Covid-19.
In contrast, antibody levels in the results of vaccine trials by Pfizer Inc. and Moderna Inc. were about the same level as those of people who had previously contracted the virus. This week, Pfizer said its experimental vaccine was 95% effective in protecting people from Covid-19, while Moderna said its vaccine was 94.5% effective based on an initial review of results at advanced stage.
Sinovac’s results are from Phase 1 and Phase 2 clinical trials, which are not designed to measure whether the vaccine is working, but can indicate whether it is eliciting an appropriate immune response. The company has not published any late-stage, or phase 3, results that measure effectiveness.
“We 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 conclusion “may simply mean that the term of protection may not be that long”.
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