A new strain of coronavirus first detected in South America last year is being found more and more in the United States, experts have warned.
Genomic modelling has found more than 1000 cases of the Lambda variant across America so far and while it's dwarfed by an explosion of new Delta cases, authorities are monitoring its spread.
"I think any time a variant is identified and demonstrates the capacity to rapidly spread in a population, you have to be concerned," Dr Gregory Poland, director of the Vaccine Research Group at the famed Mayo Clinic, told CNN.
"There are variants arising every day. The question is, do those mutations give the virus some sort of advantage, which of course is to human disadvantage? The answer in Lambda is yes."
Some 29 countries have reported cases of the Lambda variant.
It first emerged in Peru in December last year and was characterised as slow-moving but has since gathered speed and is now responsible for 90 per cent of all cases there.
Dr Adam Taylor is a researcher of emerging viruses at the Menzies Health Institute of Queensland at Griffith University and said multiple bodies are now monitoring the Lambda variant.
"Epidemiological evidence is still mounting as to the exact threat Lambda poses, so 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," Taylor, a leading virologist, wrote in an article for The Conversation.
"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."
Mutations that affect the spike protein of coronavirus can make it more infectious and the Lambda strain contains a number of them, Taylor said.
It's just not yet clear whether that will make Lambda a more worrying version of Covid.
"Preliminary data on the Lambda spike protein suggests it has increased infectivity, meaning it's more easily able to infect cells than the original Wuhan virus and the Alpha and Gamma variants," he said.
"It's worth noting infectivity is not the same as being more infectious between people. There's not enough evidence yet that Lambda is definitely more infectious, but the mutations it has suggest it's possible."
Early studies also suggest the Chinese-developed CoronaVac vaccine is less effective in combating the Lambda strain, Dr Taylor wrote.
It's also too soon to determine if the Lambda variant produces a more severe illness or an increased risk of death.
One promising indication is that Lambda has been present in the US for several months, but instances there remain "quite rare", Dr Preeti Malani from the University of Michigan, told CNN.
"Thankfully studies suggest that the currently available vaccines remain protective. We have learned during the pandemic that things can change quickly, so controlling the spread of Covid-19 in general will help manage Lambda."
The Delta variant should serve as an early warning about the impact of vaccine complacency and the risk of rollout delays.
Highly infectious and responsible for more severe illnesses and a higher risk of death, the variant emerged out of an explosion of cases of coronavirus in India.
As Covid jumps from person to person, it changes a little bit with each new infection just like any other virus, Poland told CNN.
Those changes or mutations could be benign, or there's a chance a new strain could speed up transmissibility or present a greater danger, he said.
Allowing Covid to spread is like playing "Russian roulette".
Getting vaccinated reduces the chance of mutation – including the emergence of a strain that's resistant to antibodies.
"We will continue to develop more and more variants, and eventually, one or more of these variants will learn how to evade vaccine-induced immunity," he warned.
"And if that's true, we will start all over again."
Just as the world seemed to be getting the upper hand on Covid, along came the Delta variant to knock us back down to Earth again.
Now that experts are turning their attention to the Lambda strain of the virus, many might be wondering whether this rapid mutation of coronavirus is normal.
In short, yes, Professor Sunil Lal from Monash University explains.
"The emergence of new virus variants isn't unusual, and coronaviruses are no different," said the microbiologist.
"With increased virus replication, we give the virus a higher chance for mutations to occur, hence the new variants. A majority of these new mutations are innocuous. However, some may evolve to become more infectious, or evade human antibody responses."
This has been observed in past pandemics and is a phenomenon called "convergent evolution".
For example, the Delta variant – which first originated in India – is some 60 per cent more infectious than the original strain of Covid and is blamed for new outbreaks in almost 100 countries.
We will see more and more variants until the spread of the virus is drastically slowed, Malani said.
"The only way out is widespread vaccination to control spread and prevent further mutation of [coronavirus]. It's a race between getting enough of the world vaccinated and the development of new variants that are less responsive to countermeasures."