The first published study of the experimental vaccine from Walvax Biotechnology Co., Suzhou Abogen Biosciences Co. and the Chinese military generated twice the level of neutralizing antibodies seen in people who had recovered from a Covid-19 infection, though only at an intermediate dose. People given slightly more or slightly less produced fewer of the protective antibodies than those who recovered from an earlier infection, the study found.

The trial of the vaccine known as ARCoV involving 120 volunteers was published in the journal Lancet Microbe. Six of the 20 people getting the best dose, or 85%, developed a fever. There were no serious complications in the trial, which is from the first of three stages needed to get approval.

Because the vaccine only generated more antibodies compared to previous infection at a precise dose, it may be difficult in the real world to administer the exact amount and reap the full benefit, said Mia He, an analyst with Bloomberg Intelligence. Side effects may also be an issue, with the vaccine causing more fevers than rival shots that are already on the market, she said.