Summer holidays face a new threat after the World Health Organisation (WHO) warned that Covid vaccinations should not be used to determine whether people can enter a country.
The WHO said there were still "critical unknowns" about the efficacy of vaccinations in reducing transmission and preventing the virus even as governments work on vaccine certificates as a way to kickstart travel.
It said that, as a result, national authorities, airlines and travel operators "should not introduce requirements of proof of Covid-19 vaccination for international travel as a condition for departure or entry".
Vaccination should not exempt travellers from having to undergo other "travel risk-reduction measures", such as testing or quarantine, it added.
Vaccination documents are seen as critical to enable holidaymakers to travel abroad this summer. In his roadmap out of lockdown, announced on Monday, Boris Johnson signalled that international travel could restart as early as May 17.
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Mr Johnson will make a decision after a Department of Transport investigation into how it could be safely done, which is due to report on April 12. The WHO will, however, only review its position on use of vaccination proof for entry or departure in three months.
Its concerns centre on the efficacy of vaccines in preventing the virus and limiting transmission, including of Covid variants, the length of protection they offer, whether they guard against asymptomatic infection and how long it should be before travel vaccines should be offered.
The WHO is also concerned about potential discrimination against those who might not have or do not have access to vaccinations.
Industry sources said governments, airlines and travel operators were free to ignore the organisation, but its stance could hinder the use of vaccination documents as an alternative to expensive tests or other restrictions.
Greece and Israel have already agreed to recognise vaccination certificates for travel between the two countries, while the UK and most EU governments are considering or developing similar digital documents.
The WHO has commissioned experts to help devise international standards for the digital certificates, which would be similar to yellow fever cards, despite concern about their application but in anticipation that they will be a feature of travel.
Trade organisations such as the IATA, the international airlines body, are concerned that delays by governments and other agencies in developing them threaten attempts to restart travel in time for the summer.
On Thursday, EU leaders are expected to confirm a continuing ban on non-essential travel, but senior commission officials say "there is a will" to have summer holidays.
Spain and Greece are pushing ahead with vaccine certificates and have already established protocols for their use in hotspots such as the Canary Islands and Balearics. They want to go with an EU-wide vaccine certificate scheme, but that is dependent on hitting targets to inoculate 70 per cent of countries' populations by late summer.
Priti Patel, the Home Secretary, warned on Wednesday that it was "far too early" for people to book a holiday abroad, suggesting they should wait for the Government's global travel taskforce to report on April 12. She said: "We have to look at the data at every single stage, and the road map outlined by the Prime Minister makes that abundantly clear."
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