Raina MacIntyre, who heads the biosecurity program at the Kirby Institute of the University of New South Wales in Sydney, Australia, said she would not recommend the emergency use of vaccines before the conclusion of Phase 3 trials. AstraZeneca, the British-Swedish company, halted late-stage testing in the United States on a vaccine candidate this month after one volunteer fell seriously ill for unknown reasons.
Flawed vaccines can cause significant health problems. In 2017, children who were injected with Sanofi’s dengue vaccine became sicker. Children vaccinated against respiratory syncytial virus, or R.S.V., in the 1960s also suffered side effects, resulting in trials being scrapped.
Broad inoculation campaigns also increase the risk of getting multiple vaccines, which could have adverse effects on a person’s immune response.
“It may be three to six months before we get Phase 3 trial results — it’s not that long to wait,” Dr. MacIntyre said. “You are potentially muddying the waters for the time when we do have Phase 3 trial data for the best possible vaccine.”
Still, China may not want to wait.
In an interview with China Central Television, the state broadcaster, Mr. Zheng, the health official, said that when cold weather arrived, the government might consider expanding the scope of who qualified for emergency use, adding people who work in markets, transportation and the service industry.
“The goal is to first establish an immune barrier among special populations, so that the operations of the entire cities will have a stable guarantee,” Mr. Zheng said.
The vaccine makers and local governments stress that participation is voluntary, and many people who take the vaccines pay a considerable amount to do so. According to government notices, the vaccines would cost about $148, putting them out of reach for many in a country where 600 million people make that much in a month.