As the world battles against the Delta variant of Covid-19, it's a lesser-known mutation that has experts worried.
Lambda (also known as variant C37) was first seen in Peru in August 2020. Since then, it has spread to 29 countries, mainly in South America.
While research into the strain is still in its early days, data so far suggests a couple of key features of the variant which have experts worried.
Like the Delta variant, it is highly transmissible and it may be able to dodge vaccines more readily than the original version of the virus.
It accounts for more than 80 per cent of all Covid-19 cases in Peru, according to its National Institute of Health.
Dr Pablo Tsukayama, a molecular microbiologist at Cayetano Heredia University, Lima, said indications are that Lambda is more transmissible.
"When we found it, it did not attract much attention," he told Al Jazeera.
"But … by March, it was in 50 per cent of the samples in Lima. By April, it was in 80 per cent of the samples in Peru," he said.
"That jump from one to 50 per cent is an early indicator of a more transmissible variant."
In June, Lambda was added to the World Health Organisation's (WHO) list of variants of interest. WHO defines a variant of interest as one which has genetic changes that affect things such as transmissibility, disease severity and immune escape, and has been shown to be responsible for significant community transmission in multiple countries.
So far, Lambda has reached 29 countries around the world.
In an article for The Conversation, Dr Adam Taylor of the Menzies Health Institute at Queensland's Griffith University wrote that the exact threat Lambda poses is still unknown.
"At this stage more research is required to say for certain how its mutations impact transmission, its ability to evade protection from vaccines, and the severity of disease," he said.
"Preliminary evidence suggests Lambda has an easier time infecting our cells and is a bit better at dodging our immune systems. But vaccines should still do a good job against it."
It's that last point that the world is on edge about.
Lambda has a few defining mutations to the spike protein, according to Taylor. One mutation is associated with reduced susceptibility to virus-generated antibodies.
"This means antibodies generated from being infected with the original Wuhan strain of Covid aren't quite as effective at neutralising Lambda," he wrote in The Conversation.
Another mutation is similar to the Delta variant.
"This mutation in Delta not only increases the ability of the virus to infect cells, but also promotes immune escape meaning the antibodies vaccines generate are less likely to recognise it," Taylor wrote.
It is this mutation, according to virologist Dr Ricardo Soto-Rifo of Chile's Institute of Biomedical Sciences, which may be the reason for the strain's high infection rate. In research not yet peer-reviewed, Soto-Rifo assessed the Chinese CoronaVac vaccine on Lambda. It showed the variant could neutralise the antibodies created by the vaccine.
"These results were expected," Soto-Rifo told Al Jazeera. "The virus has changed and that can make the vaccine not as efficient as it was with the original virus, but that doesn't mean the vaccine doesn't work any more."
In another non-peer-reviewed study, Dr Nathaniel Landau, a microbiologist at the NYU Grossman School of Medicine, showed a lab-made Lambda-like virus was twice as infectious as the original coronavirus.
Despite the results, he still advised vaccines were imperative.
"The key is that [Delta and Lambda are] both highly transmissible viruses. But if you get the vaccine, you're most likely going to be protected," Landau told National Geographic. "And the rate of infection with these viruses is going to go down in areas where people get the vaccine," he said.
"We believe that, at least for the mRNA vaccines – Moderna and Pfizer – that those vaccines will protect very well against Lambda, in the same way that they protect against the Delta virus.
"Even though some of the antibody no longer works against the variants, it's still enough that they will fight the virus and get rid of it pretty well."
Peru is a country in political upheaval, which is fighting a losing battle against the coronavirus pandemic.
The country has just sworn in a new left-wing president, Pedro Castillo, after a nail-biting election with the slimmest of margins.
His campaign centred on distributing wealth more evenly, winning him votes from the poor rural regions.
Early in the pandemic, Peru was quick to bring in restrictions to help curb the spread of the virus. But case numbers continued to rise.
In a nation of just over 32 million people, official records have Covid-19 deaths at 180,000. It gives the country the highest Covid death rate per head of population in the world.