Scientists have said that the lifting of restrictions for fully vaccinated arrivals to the UK from the EU and US, which begins from Monday, is not without risk.
From 4am on Monday, those who have been fully vaccinated in the US and Europe will be treated the same as British residents, meaning arrivals from amber list countries will not have to quarantine when entering England, or test on day eight after arrival.
Instead they will only be required to complete a pre-departure test and PCR test on or before the second day after arrival – although different rules will apply to those travelling from France.
While the shift is likely to be welcomed by travellers, scientists have sounded a note of caution.
Prof Rowland Kao, an epidemiologist at Edinburgh University, said the risk lies in simultaneously opening up borders to fully vaccinated people while allowing the virus to spread so that large numbers of the population in the UK are infected.
That situation, he said, is of concern, as fully vaccinated people “while relatively low risk for Covid, would by definition have a similar risk of carrying ‘escape mutants’ which evade the vaccines”, adding that with high levels of spread it would be “difficult to stamp out any such variants, should they be brought in from overseas”.
One complication is that with high levels of infection, there has been a decline in the proportion of positive samples analysed through genome sequencing, or the more rapid approach known as genotyping, to determine the variant they contain.
“As this is the principal means by which we identify variants, it would mean that stopping or even slowing down the spread of any variants in the country will be very difficult,” said Kao, who is a participant of Spi-M (the Scientific Pandemic Influenza Group on Modelling).
“Of course should the currently encouraging signs of dropping cases continue, we should soon be in a position where the greatest risk has passed – however, some delay in lifting restrictions would be epidemiologically sensible.”
Prof Julian Hiscox, chair in infection and global health at the University of Liverpool, who is a participant in the New and Emerging Respiratory Virus Threats Advisory Group (Nervtag), which advises the government on the dangers posed by new respiratory viruses, also urged caution.
“As with all things Covid-related there is a balance between infection and the consequences for human health and other factors such as the economy and people having fun,” he said.
“Whilst case rates and the corresponding chance of new variants are high, prudence would dictate a more cautious approach.”
But Prof Adam Finn of the University of Bristol, who is a member of the Joint Committee on Vaccination and Immunisation, said there could be benefits from the change in rules.
“We know that fully immunised people can become infected. They are much less likely to get seriously ill than unimmunised people when infected, including with delta and other variants, and somewhat less likely to get infected at all,” he said.
“Evidence is only now emerging as to whether, when infected, they are less likely to infect others, but this is likely to be the case at least to some extent.
“According increased freedoms to vaccinated people combined with continued testing before and after travel therefore makes some logical sense, but of course carries with it some continued risk of importation of virus.
“As in other areas of policy, it’s a balancing act trying to find the best compromise between too much risk and too much caution. If it encourages more people to get fully vaccinated, that is of course a bonus for them and for everyone else.”
Prof Peter Openshaw of Imperial College London, who is another participant in Nervtag, also said the rule change made sense from an immunological point of view.
“In terms of harmonisation of recognition of vaccines being delivered elsewhere, that also seems perfectly sensible, as long as it is countries that have proper monitoring and recording of vaccines being delivered,” he said.
But, Openshaw added, it is very difficult for politicians when they are relying on preliminary information, for example around transmission. “A lot of this is based on quite tenuous evidence,” he said.
Dr Michael Head, senior research fellow in global health at the University of Southampton, said there could be a middle ground when it comes to the rule change.
“For recent international arrivals who have received two doses, replacing quarantine with daily testing would be a reasonable pragmatic compromise,” he said.