A new coronavirus variant named Mu could be more resistant to vaccines, the World Health Organisation has said.
B.1.621 (Mu) was first identified in Colombia and cases have been recorded in South America and Europe.
The WHO has designated Mu a variant of interest and said the strain had mutations suggesting it could be more resistant to Covid-19 jabs.
“The Mu variant has a constellation of mutations that indicate potential properties of immune escape," The WHO said in its weekly bulletin.
“Preliminary data presented to the Virus Evolution Working Group show a reduction in neutralisation capacity of convalescent and vaccinee sera similar to that seen for the Beta variant, but this needs to be confirmed by further studies.”
The WHO said the global prevalence of Mu among sequenced cases has declined and is currently below 0.1%, but the prevalence in Colombia (39%) and Ecuador (13%) has consistently increased.
It added: “The epidemiology of the Mu variant in South America, particularly with the co-circulation of the Delta variant, will be monitored for changes.”
Meanwhile, South African scientists have also detected a new coronavirus variant with multiple mutations known as C.1.2, but are yet to establish whether it is more contagious or able to overcome the immunity provided by vaccines.
The strain was first detected in May and has now spread to most South African provinces and to seven other countries in Africa, Europe, Asia and Oceania, according to research which is yet to be peer-reviewed.
C.1.2 contains many mutations associated with other variants with increased transmissibility and reduced sensitivity to neutralising antibodies, but they occur in a different mix and scientists are not yet sure how they affect the behaviour of the virus.
Laboratory tests are underway to establish how well antibodies neutralise the variant.
South Africa was the first country to detect the Beta variant, one of only four labelled "of concern" by the World Health Organisation (WHO).
Beta is believed to spread more easily than the original version of the coronavirus that causes Covid-19, and there is evidence vaccines work less well against it.
Richard Lessells, an infectious disease specialist and one of the authors of the research on C.1.2, said its emergence tells us "this pandemic is far from over and that this virus is still exploring ways to potentially get better at infecting us".
He said people should not be overly alarmed at this stage and that variants with more mutations were bound to emerge further into the pandemic.
The variants of concern are the Alpha variant – first recorded in Kent – seen in 193 countries, Beta in 141, Gamma in 91 and Delta in 170 countries, while Mu is the fifth variant of interest.