The World Health Organisation has advised all over-60s to immediately postpone travel plans in light of the new Omicron variant.
Others at risk of developing severe Covid symptoms should also shelve trips, WHO stated.
New advice was issued to people worldwide in the wake of the new variant, described as the most concerning yet discovered by worried experts.
The organisation also urged countries to remain calm and take "rational" measures against the fast-spreading mutation.
They also warned that blanket travel bans will not prevent the international spread of the variant despite some calls to totally close borders.
"Persons who are unwell or at risk of developing severe Covid-19 disease and dying, including people 60 years of age or older or those with co-morbidities (e.g. heart disease, cancer and diabetes), should be advised to postpone travel," the WHO said in a travel advice statement.
The UK has joined other countries in imposing a travel ban on South Africa.
However, a complete travel ban will not prevent the global spread the variant, they added.
The statement went on: “Blanket travel bans will not prevent the international spread, and they place a heavy burden on lives and livelihoods.
"In addition, they can adversely impact global health efforts during a pandemic by disincentivizing countries to report and share epidemiological and sequencing data."
Countries should apply "an evidence-informed and risk-based approach" with any travel measures related to the Omicron variant of the coronavirus, they state,
That including possible screening or quarantine of international passengers.
It comes as Prime Minister Boris Johnson told Brits not to cancel Christmas plans - and stressed there is no immediate lockdown threat.
He stressed they want to take a "balanced and proportionate" approach to Omicron, which has now seen confirmed UK cases rise to 22.
There are 13 in England, with nine in London.
But 400 military personnel have been brought in to help - with more vaccine centres to "pop up like Christmas trees".
The PM outlined the target to have offered everyone over 18 a booster jab by the end of January.
