The World Health Organization (WHO) welcomed a report by Moderna on Monday that its experimental vaccine had showed 94.5% efficacy, but said that "many questions" remained and that it was no time for complacency.
Only very limited amounts of any vaccine will be available in the first half of 2021 for people other than priority health workers, WHO officials said.
"While we continue to receive encouraging news about COVID-19 vaccines and remain cautiously optimistic about the potential for new tools to start to arrive in coming months, right now we are extremely concerned by the surge in cases we are seeing in some countries, particularly in Europe and the Americas," WHO director-general Tedros Adhanom Ghebreyesus told a news briefing.