Dr Jenny Harries, UK Health Security Agency chief executive, was tackled on the issue by the government’s transport committee on Wednesday (15 December).
"In relation to vaccination, this gets very, very complicated," she said. "There is not unreasonably a perception that until Omicron came along, if you are vaccinated, you couldn’t be infectious.
"Vaccines are brilliant... but you actually can still transmit infection. It’s why there is a complete logic in having a pre-departure test while still being vaccinated, because it protects you as an individual, it protects the population as a whole, but it doesn’t actually mean you’re not infectious when you get on that aeroplane or that boat."
Harries said the emergence of Omicron had "thrown that up in the air as well".
"The likelihood of you being infectious, even with two doses, is actually quite high. So I think we should start to try and dissociate the fact that we have a vaccinated population who are likely to be protected against some variants themselves.
"You will not necessarily not be a risk to others, you may still be infectious and I think what this shows is it’s really important that we consider every variant as it comes through. You’re reducing the risk of the individual transmitting to somebody else.
"The benefit of the test is it signals a risk and then the individual needs to isolate and it’s the testing and the isolation together which means the individual no longer is a threat to anybody else."
Committee chair Huw Merriman MP asked why the focus was on those flying into the country. "We don’t do that in terms of getting the train up to Edinburgh or even flying up to Edinburgh," he said. “Why pick on the international traveller?"
Harries argued there was actually similar thinking within the UK, adding: "One of the differences with the border is we have the possibility of new variants coming, we have a better understanding because we have much higher testing levels in the UK than many other countries or we have access to that data."
Merriman pointed out that many "expensive PCR tests" that proved positive were not further examined to detect variants. He said July saw 500,000 people tested in three weeks via PCR, with 7,000 being positive, with only 5% tested for variants of concern and asked: "Doesn’t that actually render it an expensive white elephant?"
Harries replied that all positive tests by travel providers "should be put through for sequencing". All hotel quarantine tests were sequenced, she said.
She said the need for arrivals testing was proved because if pre-departure tests were used, "we should not be seeing more than 1% of people coming through being positive, and yet in some countries that is not the case".
