People in the UK have been warned that foreign holidays this summer are 'extremely unlikely' as concern builds in the EU.
It comes as countries across Europe have had to impose tougher restrictions amid a rise in Covid-19 cases.
Dr Mike Tildesley, a member of the Spi-M modelling group which advises the government, said there was a danger that new variants could jeopardise the vaccination programme later in the year.
Other experts have warned there could be a third wave of Covid-19 infections in the UK and advised people not to consider overseas holidays when restrictions ease later this year.
Infectious disease expert Dr Tildesley told BBC Radio 4's Today programme: "I think that international travel this summer is, for the average holidaymaker, sadly I think, extremely unlikely.
"I think we are running a real risk if we do start to have lots of people going overseas in July and August because of the potential for bringing more of these new variants back into the country.
"What is really dangerous is if we jeopardise our vaccination campaign by having these variants where the vaccines don’t work as effectively spreading more rapidly."
The rise in coronavirus infections in Europe, which could last "several months" and shows the need for the UK to be "careful" as it releases lockdown measures, an expert has warned.
Andrew Hayward, professor of infectious disease epidemiology at University College London (UCL) and a member of the Scientific Advisory Group for Emergencies (Sage), told Times Radio that it was "very worrying" for Europe to be moving into a "third wave" of coronavirus cases with "comparatively low vaccination levels".
Speaking to the station in a personal capacity, he added: "From what I understand, quite a lot of that is the emergence of the strain that came from the UK, the B117 strain, which is more transmissible, which is the same strain that’s still here now.
"I think it just shows that the lockdown in the UK is necessary and we need to be careful as we release and to watch the figures because this shows the potential for cases to shoot up.
"Obviously it has implications on travel, I think, and what we plan for doing with that, because these waves of infection will tend to last for several months really before they get back down to low levels.
"But unless there's much travel between the countries it shouldn’t directly impact us."
Prof Andrew Hayward added that "another wave" of coronavirus cases was possible in the UK but its consequences would be less due to high levels of vaccination.
