The makers of coronavirus vaccines are figuring out how to tweak their recipes against mutations as the UK's newly established quarantine hotels receive their first guests and infection rates appear to be dropping off in the US.
Passengers arriving at London's Heathrow Airport on Monday morning were escorted by security guards to buses that took them to nearby hotels.
The UK has given a first dose of coronavirus vaccine to almost a quarter of the population but health officials are concerned that vaccines may not work as well on some new strains of the virus including one first identified in South Africa.
Under the new rules, people arriving in England from 33 high-risk countries must stay in designated hotels for 10 days at their own expense, with meals delivered to their door.
In Scotland the rule applies to arrivals from any country.
Meanwhile, metrics in the US indicate coronavirus infection numbers are declining sharply.
Johns Hopkins University's latest data suggests 64,194 new coronavirus infections were reported in the country on Sunday.
This is the lowest daily number in several months.
The total of US cases rose to 27,640,291.
During the same period, 1084 pandemic-related deaths were reported across the country, taking the US total to 485,336.
In terms of hospitalisations, the lowest number since November 17 was reported on Sunday.
A total of 67,023 COVID-19 patients are currently admitted in hospitals across the country, according to the Covid Tracking Project.
The US Centers for Disease Control and Prevention said that more than 70 million vaccine doses have been distributed so far in the country.
More than 52 million doses of vaccine were administered to people.
Regulators in the US and elsewhere are looking to the flu as a blueprint if and when COVID-19 vaccines need an update.
"It's not really something you can sort of flip a switch, do overnight," cautioned Richard Webby, who directs a World Health Organisation flu centre from St Jude Children's Research Hospital.
Viruses mutate constantly and it takes just the right combination of particular mutations to escape vaccination.
But studies are raising concern that first-generation COVID-19 vaccines don't work as well against a mutant that first emerged in South Africa as they do against other versions circulating around the world.
The good news is that many of the new COVID-19 vaccines are made with new, flexible technology that is easy to upgrade.
What is harder is deciding if the virus has mutated enough that it is time to modify vaccines and what changes to make.