A coronavirus vaccine candidate developed by a unit of China National Pharmaceutical Group (Sinopharm) appeared to be safe and triggered antibody-based immune responses in early and mid-stage trials, researchers said.

The candidate has already moved into a late-stage trial, one of a handful of candidates being tested on several thousand people to see if they are effective enough to win regulatory approval.

Sinopharm is testing the potential vaccine in the United Arab Emirates in a Phase 3 trial expected to recruit 15,000 people, as China has too few new cases to be a useful trial site.

The state-owned company will also supply the candidate to Pakistan as part of a trial agreement, the Wall Street Journal reported.

The shot did not cause any serious side effects, according to a paper published on Thursday in the Journal of the American Medical Association (JAMA) by scientists who are part of Sinopharm and other China-based disease control authorities and research institutes.

The results were based on data from 320 healthy adults in Phase 1 and 2 trials.

The candidate triggered robust antibody responses in inoculated people, but it remained unknown if that was sufficient to prevent COVID-19 infection, researchers developing the vaccine said in the paper.

Sinopharm's chairman told media last month that a potential vaccine could be ready by the end of this year with Phase 3 testing expected to be completed in about three months.

The novel coronavirus, which has killed more than 750,000 people globally, has prompted a race to develop a vaccine. More than 150 candidate vaccines are being developed and tested around the world.

Russia became the first country to grant regulatory approval to a vaccine after less than two months of human testing, and a shot developed by Chinese firm CanSino Bilogics has been cleared for use in the military.

China is leading the development of at least eight vaccine candidates in different stages of clinical trials.