The US Centers for Disease Control and Prevention moved the UK up to Level 4 on Monday afternoon (19 July), indicating there being risk of a "very high level" of Covid-19 infection.
"Avoid travel to the United Kingdom," read the updated CDC advice. "If you must travel to the United Kingdom, make sure you are fully vaccinated before travel.
"Because of the current situation in the United Kingdom, even fully vaccinated travellers may be at risk for getting and spreading COVID-19 variants," the CDC added.
The US State Department continues to advise people to "reconsider" travel to the UK, with it remaining at Level 3 under its separate travel advisory regime.
The Foreign Office, meanwhile, eased its Covid-specific travel advice for the US earlier this month.
The US is on the UK’s amber list, meaning fully vaccinated arrivals from the US no longer have to self-isolate for 10 days on arrival.
