The risk of COVID variants being brought into the UK from the US and EU could rise when fully vaccinated travellers are allowed in without quarantining.
From Monday, passengers who have been fully vaccinated in the US or EU amber list countries will be exempt from isolating for 10 days.
This brings those travellers in line with people vaccinated in the UK returning but Labour and the Welsh government have raised concerns the move will mean other COVID variants could be brought into the UK.
Two variants are of particular concern: the Beta and Gamma variants first detected in South Africa and Brazil, respectively, as vaccines are slightly less effective against them and the Gamma spreads more quickly.
In most countries, the Alpha (first detected in Kent) and the Delta (first detected in India) are the most prevalent variants.
A total of 276,772 Alpha cases have been confirmed in the UK (406 in the past week) and 286,765 Delta cases (33,716 in the past week).
The latest data from Public Health England (PHE) found no cases of the Beta variant in the UK and just over 0% of the Gamma.
Since Beta was detected in South Africa in December last year there have been 1,082 cases in the UK, with nine in the last week.
And since Gamma was detected in Brazil in November last year, there have been 254 cases in the UK, with none in the past week.
Both the EU and the US have recorded higher proportions of the two variants, but the Beta is more prevalent in the EU than in the US, while the Gamma is more widespread in the US than the EU.
The US has relatively low numbers of the Gamma variant, but still much higher than the UK.
Some countries in Europe, especially Luxembourg, have seen the Gamma take over as their dominant variant.
Are the vaccines still effective against the Beta and Gamma variants?
The vaccines available in the UK have been found to be less effective against the Beta and Gamma variants, but still offer a high protection against being admitted to hospital with COVID-19 or dying from it.
AstraZeneca recently reported one dose was 82% effective against serious disease from Beta and Gamma, 87% effective against the Delta and 90% against the Alpha.
Its efficacy against symptomatic but not serious disease was 50% for the Beta and Gamma variants, 70% for the Delta and 72% for the Alpha.
Previous trials have found AstraZeneca's effectiveness increases after two doses so the latest study authors said the lower protection against milder disease was expected after just one dose instead of two.
South Africa halted its AstraZeneca rollout as clinical trials showed a lack of protection against mild or moderate illness caused by the Beta variant.
In a recent study, yet to be peer-reviewed, the Pfizer vaccine, 14 days after the second dose, was found to be "at most marginally affected" by the Beta variant, with 94% effectiveness compared with 95% protection against the Alpha variant.
Another study found a single Pfizer jab was 83% effective against the Beta and Gamma variants at preventing hospitalisation and death after 21 days.
A second dose boosted efficacy to 98% 14 days after the jab, the study found.
Pfizer announced earlier this month it has seen waning immunity from its vaccine against all variants over time and is ramping up efforts to develop a booster dose, although the US has said boosters are not needed yet.
One dose of Moderna's vaccine was found to be 77% effective at preventing hospital admissions and deaths from the Beta and Gamma vaccines 14 days after a first dose and 84% seven days after the second.
Its original efficacy was 94% after two doses.