COVID variants that came to the UK from India and Thailand show Brits must be stopped from holidaying, an expert has warned.
Professor Christina Pagel said new variants “are coming from everywhere”.
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And the most recent to land on British soil was first detected in Thailand in travellers from Egypt.
Prof Pagel, a mathematician who specialises in health data and professor of operational research at University College London, said: “Neither of those cases are on the red list.
“We now have 100 cases and it has a concerning mutations.”
She told BBC Radio 4’s Today programme: “New variants are coming from everywhere and this summer we need to protect our vaccine programme.
“There is no particular reason to think this variant will be the last to become dominant in the UK.”
Both Egypt and Thailand are “amber list” countries, which means people can enter the UK without needing to quarantine at a Government approved hotel.
Instead, they only have to self isolate at home for ten days.
Dozens of other countries are on the list, allowing Brits to freely travel between them.
While a small handful including Portugal are on the “green list”, making zero-hassle holidays possible.
Spain is on the amber list, and this week lifted travel restrictions for UK travellers.
Up to 100,000 Brits are expected to head to Spain this week for sunshine despite the Government advising against holidays.
Prof Pagel has called for international travel and the June 21 unlocking to be delayed by a couple of months.
During this time more people will get a second dose, which will put the country in a “much, much better position” against new variants.
Any new variant that weakens vaccine efficacy alters how protected the population is from disease burden.
The Indian variant, which is surging in the UK, already threatens the value of vaccines, given that they do not work as well against it.
Two doses of either the AstraZeneca or Pfizer vaccine offer at least 66 per cent protection – which is halved with only one dose.
Only around four in ten adults have had two doses of their vaccine, which is “not good dose coverage”, Prof Pagel, a member of Independent Sage, said.
Public Health England (PHE) revealed the new variant under investigation from Thailand is known as C.36.3.
The agency said 109 cases had been found in the UK. Most are in London (33) followed by Yorkshire (20).
Officials stressed there is no evidence that the new strain causes more severe disease.
They said it had been designated as “under investigation” because of the number of mutations it had, and “increased importation from a widening international area”.
Meanwhile, Health Secretary Matt Hancock revealed “as many as three-quarters” of all new cases are now the super infectious Indian strain.
Cases of the Indian variant of Covid-19 reached almost 7,000 – double the figure given a week ago.
Professor Andrew Hayward, from University College London and a member of the Sage group Nervtag, warned: “It only takes five or six doublings for that to get up to say a quarter-million cases, and then you could set the pressure on the NHS and avoidable illnesses.”
He said when further restrictions were lifted “instead of doubling every week it’s likely to double more frequently than that of course”.
“So I think there is a good argument for caution until such time as we’ve got a much higher proportion of the population double vaccinated”, he added.
Dr Jenny Harries, chief executive of the UK Health Security Agency, says the numbers of cases had become “quite worrying”.
She added “the number in hospitals across the country remains low” – however, data shows that figures are up in hotspots like Bolton.
Despite the growing concern, the PM repeated to reporters on Thursday he “didn’t see anything currently in the data” to divert from next month’s target.
But he added: “We may need to wait.”
Dr Mike Tildesley, from the University of Warwick and a member of the Scientific Pandemic Influenza Group on Modelling (Spi-M) group, said more research was needed to understand what could happen should the June 21 step go ahead.
He said it was expected cases would go up because some restrictions have been lifted.
“Obviously the worry is that, because it’s a bit more transmissible, then there is the potential for a further wave of infections and potentially hospital admissions will start to rise again,” he added.
But he told BBC Breakfast “it seems like the vaccines work pretty well, particularly after a second dose”.
And the jabs mean “we are in a very different place from, say, in October when we were starting to see cases rising in a concerning way”.