The so-called Brazil variant may evade up to 61% of the immunity brought about after people overcome older versions of the coronavirus, research suggests.
There are six known cases of the Brazil variant in the UK, one of which health officials are still trying to trace after they left their contact details off their coronavirus test registration card.
The emergence of new variants raises questions as to whether they will spread more readily, cause more serious complications or even evade a former coronavirus patient's natural immunity, as well as that brought about by the long-awaited vaccination programme.
To learn more, scientists from around the world screened virus samples collected in Brazil, with results suggesting its variant may evade between 25% and 61% of the immunity brought about after an individual overcomes a different version of the coronavirus.
While it may sound alarming, Professor Sharon Peacock – director of the COVID-19 Genomics UK Consortium – stressed the results should be interpreted with a "note of caution", with there being limited evidence the Brazil variant will "threaten our vaccine strategy or effectiveness".
The results are preliminary and yet to be published in a peer-reviewed journal.
Viral mutations are entirely expected, with the majority having a neutral effect.
Concerns were raised, however, when coronavirus cases spiked in Manaus – the largest city in the Amazon – despite incidences already being high in that region.
Genetic sequencing of virus samples collected between November 2020 and January 2021 revealed a "variant of concern" had emerged.
Now known as the "Brazil variant", it has 17 mutations, three of which affect the virus' spike protein, potentially aiding entry into cells.
The spike protein binds to a cell's so-called ACE2 receptor, allowing it to invade the body. The protein is also a target for many vaccines.
Using a "dynamic model" made up of genetic and death data, the global scientists estimate the Brazil variant is 1.4 to 2.2 times more transmissible than previously circulating versions of the coronavirus.
The Brazil variant may also be able to evade 25% to 61% of "protective immunity elicited by previous infection" with other versions of the virus, the results suggest.
To put this into context, "if 100 people were infected, 25 to 61 are susceptible" to the Brazil variant, according to study author Dr Nuno Faria, from Imperial College London.
While it may sound alarming, Professor Peacock stressed the research was carried out in Brazil, with the results not necessarily applying to the rest of the world.
"How they relate to the UK is yet to be determined," she said. "I would express a note of caution."
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When it comes to how the Brazil variant may impact vaccine effectiveness, experts are cautiously optimistic, but still unsure.
Studies have suggested the UK's three approved jabs – Pfizer-BioNTech, University of Oxford-AstraZeneca and Moderna – are effective against the so-called Kent variant.
This was identified in the home county towards the end of 2020 and is thought to be behind the majority of the coronavirus cases arising in the UK – 5,455 on 1 March.
The three approved vaccines are also thought to protect against severe disease brought about by the so-called South Africa variant, but perhaps to a lesser extent.
Speaking amid the latest research, Professor Peacock said: "We should be pushing on with vaccination.
"The number of [Brazil variant] cases are very low at the moment.
"I don't believe there's any threat to our vaccine strategy or effectiveness.
"You can't take a study like this and speculate on vaccine efficacy.
"Vaccine manufacturers will be looking to make adaptations to their vaccines so people can have boosters.
She added: "It's a note of optimism, but a note we need to work with vaccine developers to ensure we have vaccines [that are] effective for our population."
Dr Faria agreed, stressing "there is nothing to suggest the vaccines won't work" against the Brazil variant.
Professor Andrew Pollard – who led some of the clinical trials for the Oxford-AstraZenca vaccine – told BBC Today work is underway to uncover if the jab is effective against the Brazil and South Africa variants, which are "distributing themselves to many countries".
The University of Oxford medic hopes people can move away from an "obsession" with each emerging variant.
Dr Susan Hopkins, from Public Health England, added: "This variant that emerged in Manaus in Brazil is really quite similar to the [variant] from South Africa and they have a number of mutations that are suggested to increase transmissibility.
"Manaus in particular reported a number of individuals were reinfected with this variant, and therefore that suggests having had prior immunity from primary infection wasn't enough to reduce infection and transmission, and that may also impact on the vaccine."
Some believe vaccine effectiveness may be reduced, but is highly unlikely to be eliminated altogether.
Dr Jeffrey Barrett, who genetically sequences coronavirus samples at the Wellcome Sanger Institute, also told the Today programme: "I think there is some laboratory-based evidence it [the Brazil variant] is partially less neutralised by vaccines.
"I don't think we know how much of a difference that will make in the real world.
"We certainly don't think it will be completely able to escape vaccination."
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