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Six COVID-19 vaccine candidates, including three from China, have entered phase-3 trials, a senior World Health Organization (WHO) official said on Thursday.

The three Chinese candidates are from Sinovac, Wuhan Institute of Biological Products/Sinopharm and Beijing Institute of Biological Products/Sinopharm, said Michael Ryan, executive director of the WHO Health Emergencies Program, at a virtual briefing.

The other three are made by the University of Oxford/AstraZeneca, Moderna/NIAID and BioNTech/Fosun Pharma/Pfizer, he added.

The vaccines will be put into the general population for the first time in phase 3, after previous trials have focused on safety, immunogenicity and immune response in a small number of humans, said the WHO official. The phase-3 trial will test whether the vaccines can "protect large numbers of people over a prolonged period of time."

However, "phase-3 doesn't mean nearly there," he said, as "there is no guarantee that any of these six will give us the answer."

In total, 165 vaccine candidates have started some forms of trials, and 26 of them in clinical trials, according to WHO records.