A new strain of the coronavirus discovered in the UK has mutations seen in both the highly infectious B22.214.171.124 variant and the South African one, the latter having been shown to reduce the effectiveness of the first batch of vaccines.
B.1.525 has been listed as of "biological significance" by researchers from Edinburgh University. It not only shares traits with B.1.1.7, but has the dreaded E484K mutation found in variants from South Africa and Brazil, as well two new ones.
E484K reduces the effectiveness of the current leading vaccines, studies have shown, including those from Pfizer/BioNTech, AstraZeneca and Moderna.
More than 130 cases of B.1.525 dating back to December 15 have been picked up worldwide - 39 in the UK, 38 in Denmark, 29 in Nigeria, 10 in the US and a handful in other countries including Canada, France, Ghana, Australia, Jordan and Singapore.
Its origin remains unknown - the UK leads the world in genomic sequencing, so has a good chance of detecting new strains first even if they originate elsewhere.
"Fortunately, it doesn't seem to be spreading any faster than other strains and it's still at very, very low levels," epidemiologist Andrew Hayward of University College London told BBC News.
"With all of these variants, we really need to be keeping a very close eye on them because we don't know what they will do."
The British B.1.1.7 strain thankfully appears to be no match for the Pfizer/BioNTech vaccine, early data from Israel's rapid rollout suggests.
"Public Health England is monitoring data about emerging variants very closely and where necessary public health interventions are being undertaken, such as extra testing and enhanced contact tracing," said director of health protection Yvonne Doyle.
There have been 22 detected cases of B.1.1.7 itself with the E484K mutation, UK government data shows. B.1.525 has two extra mutations of concern - known as F888L and Q677H.
It's still too early to say whether B.1.525 will spread as easily as B.1.1.7. The UK has been on lockdown since the start of January, which has dramatically cut infection rates.
"The best way to stop the spread of the virus is to follow the public health advice - wash your hands, wear a face covering and keep your distance from others," said Prof Doyle.
"While in lockdown, it is important that people stay at home where possible."
Other variants have been picked up in Bristol and Liverpool.
Research published earlier this week found the combination of B.1.1.7 mutations and E484K "represents a threat" to Moderna's vaccine, which uses similar technology to that of the Pfizer/BioNTech vaccine. South Africa recently stopped its rollout of the UK-developed AstraZeneca vaccine over fears it wouldn't stop viruses with E484K.
Prime Minister Boris Johnson said earlier this week he'd like to set in motion an "irreversible" path out of lockdown, but case numbers had to come down further first. The UK has dished out more than 15 million first doses of the Pfizer/BioNTech and AstraZeneca vaccines.
"The idea that the vaccine has contributed to the UK's drop in cases is unclear at the moment. You have to remember they've been in a lockdown since the beginning of January," Kiwi infectious diseases expert Siouxsie Wiles told The AM Show on Wednesday.
"We're only going to find out once they start lifting restrictions what impact that one dose of the vaccine has had.
"My worry - and this is certainly a worry of many of the experts in the UK as well - is that if people haven't got both doses and don't have a good enough immune response, and you open up (and we know they're going to open up while they still have lots and lots of infectious people) you may be providing a training ground for the virus to evolve to basically escape the immune response. That would be a really quite devastating thing."
In addition to the UK's newest variant, another seven have been reported in the US and one similar to B.1.1.7 in Uganda, dubbed A.23.1.