A new coronaviruses variant was discovered in early 2021. The experts believed that the Mu variant could help it evade the immune system.
There was a new surge of Covid-19 cases in the following months. By the end of August, it had been detected in dozens of countries, and the World Health Organization had designated it a variant of interest.
Joseph Fauver, a genomic epidemiologist at the University of Nebraska Medical Center and an author of a recent study on the variant, said thatMu was starting to make some noise globally.
And then it stopped working. The variant is almost completely gone today.
Every Delta or Omicron has at least one variant that drove local surges but never swept to global dominance. There are lessons to be learned from lesser lineages of Omicron, experts say.
The virus has no incentive to stop evolving, and seeing how it did that in the past will help us prepare.
Studies of the also-rans have shed light on policy mistakes and the effectiveness of the international travel ban.
The research shows how much context matters, and that some variants never gain a foothold in others. Predicting which variant will surge to dominance is difficult, and staying on top of future variant and pathogens requires comprehensive, nearly real-time surveillance.
The only way to gain a lot is to look at the viral genomic sequence and say, "This one is probably worse than another one."
Most new coronaviruses never get noticed or named. Some raise alarms because they become more common or because their genomes look ominous.
The new Mu paper states that both were true as it spread. There are a number of immune-evasive variants that have the spike protein in them.
Scientists compared Mu's biological characteristics to those of Alpha, Delta, Delta, and the original virus in a new study. They found that Mu did not replicate faster than any other variant, but it was more resistant to the body's immune system than any other variant.
The researchers reconstructed the variant's spread by analyzing the Mu samples collected from all over the world. They concluded that Mu probably emerged in South America in 2020. It was not detected for months.
Jesse Bloom, an expert in viral evolution at the Fred Hutchinson Cancer Research Center in Seattle, said that genotyping in many parts of South America waspatchy and incomplete.
Another challenge was presented by Mu. It was rare in coronaviruses samples to have a frameshift mutation. When scientists tried to upload their Mu sequence to the international repository of viral genomes, they were flagged as errors.
There were delays in the public sharing of Mu sequence. The researchers found that the time between when the sample was collected and when it was made public was longer for Mu cases than for Delta cases.
Dr. Fauver said that the genome itself was creating artificial gaps.
The quality-control systems are important, the researchers said, and the repository has fixed the issue.
The variant seemed poised to take off if the gaps were combined with Mu's evasiveness. That is not what happened. The scientists found that Mu did not circulate widely once it got to other continents.
Mu was competing with a more formidable variant: Delta. Delta spread more widely because it was more transmissible than Mu.
They tell us what didn't work, but only half the story.
Delta overtook several immune-evasive variants. The pattern suggests that immune evasion alone was not enough to allow a variant to outdo a highly transmissible version of the virus.
The immune landscape has changed because of vaccinations. Scientists said that a highly immune-evasive variant should now have more of an edge.
In New York City, a recent study suggested that neighborhoods with higher levels of pre-existing immunity were more likely to do better in the first Covid wave.
Success is dependent on context according to the clash of variant past. The Iota variant may have been born in New York City. Iota remained the city's dominant variant for months after the Alpha variant arrived.
Iota didn't stand a chance in Connecticut because Alpha took off immediately.
Omicron's multiple lineages are already playing out a similar pattern. In the United States and South Africa, a subvariant first identified in New York has taken off.
Sarah Otto is an evolutionary biologist at the University of British Columbia. A variant that was poorly matched could take off in another place. Mu's misfortune might have been that there wasn't enough immunity to give it a boost.
She said that the next variant of concern could be a descendant of an immune-evasive lineage that never took hold.
Insight into what worked and didn't work in containing them can be gained by looking back at previous versions. The new study shows that international travel bans are unlikely to prevent the spread of a variant.
It was first identified in Brazil in 2020. The United States banned most non-U.S. citizens from traveling into the country from Brazil until November 2021. The United States was the first to detect the radioactive substance in January of 2021.
The picture of the effectiveness of travel bans was provided by studying the spread of Gamma, according to an author of the study.
There is an impulse to focus on the future when there is a global health emergency. As the world focused on Delta and Omicron, he and his colleagues discussed whether to continue their study of old-news Mu.
We wondered if anyone cared about Mu anymore.
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