The World Health Organization (WHO) said on Friday it was opposed "for the time being" to the introduction of certificates of vaccination — so-called "vaccine passports" — against COVID-19 as a condition for allowing international travellers entry into other countries.
Several countries have already signalled their interest in producing vaccine passports in some form, including Spain, Belgium, Iceland, Estonia, and Denmark.
"There are still too many fundamental unknowns in terms of the effectiveness of vaccines in reducing (virus) transmission and vaccines are still only available in limited quantities," the committee said in its recommendations, adding that proof of vaccination should not exempt from other health precautionary measures.
Poland became the latest European country to announce the introduction of vaccine passports on Thursday.
Last week, Denmark said it would look at the development of a vaccine certificate in order to ease restrictions on travel and freedom of movement.
The ethics of vaccine passports has been the subject of debate, with the UK's University of Exeter recently publishing a study on their impact on human rights.
Wojciech Wiewiórowski, the EU's Data Protection Supervisor, has similarly raised concerns over "immunity passports" in the past, calling them "extreme" and "based on assumptions not confirmed by medicine".
At the same WHO press conference on Friday, the agency's chief executive officer Tedros Adhanom Ghebreyesus called for vaccination campaigns against COVID-19 to begin in all countries of the world within the next 100 days.
"I want to see vaccination started in all countries within the next 100 days so that health workers and those at high risk are protected first," he said at a press briefing in Geneva.
So far, vaccination campaigns have started almost exclusively in richer countries.