The World Health Organization does not back requiring vaccination passports for travel due to uncertainty over whether inoculation prevents transmission of the virus, as well as equity concerns, a spokeswoman said on Tuesday.

"We as WHO are saying at this stage we would not like to see the vaccination passport as a requirement for entry or exit because we are not certain at this stage that the vaccine prevents transmission," WHO spokeswoman Margaret Harris said.

"There are all those other questions, apart from the question of discrimination against the people who are not able to have the vaccine for one reason or another," she told a U.N. news briefing.

The WHO now expects to review China's COVID-19 vaccines Sinopharm and Sinovac for possible emergency use listing around the end of April, Harris said.

"It's not coming as quickly as we had hoped because we need more data," she said, declining to provide more information, citing confidentiality.

WHO director-general Tedros Adhanom Ghebreyesus appealed last month to countries with excess vaccine supplies to donate 10 million doses urgently to the COVAX facility which it runs with the GAVI vaccine alliance. Export restrictions by India left the vaccine-sharing programme short of supplies of AstraZeneca's vaccine made by the Serum Institute of India.

Harris said she had no update on any countries stepping forward, adding: "We are very much looking for more vaccine".