The World Health Organisation's chief scientist said on Monday she expected there to be "very limited" Covid-19 vaccine doses available in the first half of 2021.
Soumya Swaminathan said that she remained optimistic that the body would be able to work with many manufacturers to have a wide selection of vaccines as part of its global distribution scheme.
The WHO said it was looking at delivery characteristics and the ease at which vaccines can be delivered, with some requiring ultra-cold storage and transport.
The organisation also said there was no time for complacency in confronting the virus, despite positive news about possible vaccines.
"Right now we are extremely concerned by the surge in Covid-19 cases we’re seeing in some countries," WHO Director-General Tedros Adhanom Ghebreyesus said.
"Particularly in Europe and the Americas, health workers and health systems are being pushed to breaking point."
A vaccine on its own will not end the #COVID19 pandemic. We will still need to continue:
-Surveillance
-Testing, isolating & caring for cases
-Tracing & quarantining contacts
-Engaging communities
-Encouraging individuals to be careful #ACTogether #EB147— Tedros Adhanom Ghebreyesus (@DrTedros) November 16, 2020
The WHO said on Monday that the fight against the coronavirus was not a choice between life and livelihoods, with both part of the same fight.
"The quickest way to open up economies is to defeat the virus," Mr Ghebreyesus told a virtual briefing in Geneva.
He said G20 leaders would meet this weekend, giving them an opportunity to commit financially and politically to the COVAX global facility, which has been set up to provide Covid-19 vaccines to poorer countries.
More than 54.44 million people have been reported infected by the coronavirus globally and 1,318,042 have died, according to a Reuters tally.
Infections have been reported in more than 210 countries and territories since the first cases were identified in China in December 2019.
