In early 2021, scientists in Colombia discovered an alarming new variant of the coronavirus. This variant, eventually known as Mu, had several disturbing mutations that experts said could help it evade the immune system’s defenses.
In the following months, Mu spread rapidly to Colombia, fueling a new influx of Covid-19 cases. By the end of August, it was found in dozens of countries and was described as an “interesting option” by the World Health Organization.
“It’s starting to make some noise around the world,” said Joseph Fower, a genomic epidemiologist at the University of Nebraska Medical Center and author of a recent study on the variant.
And then he died. Today, the option has almost disappeared.
For every Delta or Omicron, there are Gamma, Iota or Mu, variants that caused local jumps but never reached global dominance. And while understanding Omicron remains a critical priority for public health, there are lessons to be learned from these smaller lines, experts say.
“This virus has no incentive to stop adapting and evolving,” said Joel Wertheim, a molecular epidemiologist at the University of California, San Diego. “And seeing how he has accomplished this in the past will help us prepare for what he may do in the future.”
Early research sheds light on surveillance gaps and policy errors – providing more evidence that international travel bans in America have not been effective – and on what makes the virus successful, suggesting that in the early stages of the pandemic transmission is more important than avoiding immunity.
The study also emphasizes the importance of context; options that affect some places are never established in others. As a result, it is difficult to predict which variants will increase to dominance and staying on top of future variants and pathogens will require comprehensive monitoring in near real time.
“We can gain a lot by looking at the viral genomic sequence and saying, ‘This one is probably worse than another,'” Dr. Wertheim said. “But the only way to really find out is to watch it spread, because there are a lot of potentially dangerous options that have never been necessary.”
Here I look at Him
The coronavirus is constantly changing and most new variants are never noticed or named. But others are raising concerns, either because they’re fast becoming more common or because their genomes look sinister.
Both were faithful to Him when He spread to Colombia. “It contained several mutations that people observed very closely,” said Mary Petrone, a genomic epidemiologist at the University of Sydney and author of Mu’s new book. Several of the mutations in its thorn protein have been documented in other immunoavoidant variants, including beta and gamma.
In the new study, which has not yet been published in a scientific journal, the researchers compared the biological characteristics of Mu with those of Alpha, Beta, Delta, Gamma and the original virus. Mu did not replicate faster than any other variant, they found, but it was the most immune-defying of the group – more resistant to antibodies than any known variant except Omicron, Dr. Fower said.
By analyzing the genomic sequences of Mu samples collected from around the world, the researchers reconstructed the distribution of the variant. They concluded that Mu probably appeared in South America in mid-2020. It then circulated for months before being discovered.
Genomic surveillance in many parts of South America was “incomplete and incomplete,” said Jesse Bloom, a viral evolution expert at the Fred Hutchinson Cancer Research Center in Seattle. “If there had been better monitoring in these regions, it would probably have been easier to make a quicker assessment of how worried you are about Him.”
Mu also presented another challenge. There has been a type of mutation known as the frame-displacement mutation that was rare in coronavirus samples. Such mutations were marked as errors when scientists, including Dr. Fower, tried to upload their Mu sequences to GISAID, an international viral genome repository used to track new variants.
This complication created a delay in the public sharing of Mu sequences. The time elapsed between taking a virus sample from a patient and the time it was publicly available on GISAID is consistently longer for Mu cases than for Delta cases, the researchers found.
“The genome itself was actually creating artificial gaps in the observation,” Dr. Fower said. “This has led, at least in our experience, to not receiving data for weeks, when we usually try to get it out for days.”
(GISAID quality control systems are important, the researchers said, and the repository has fixed the problem.)
Combine these gaps in surveillance with Mu’s immune evasion, and the option seemed ready to go. But that’s not what happened. Instead, it radiated from South and Central America to other continents, but did not circulate widely once it reached it, scientists have found. “This was an indication that this option was not as suitable for the people of North America and Europe as we expected,” said Dr Petrone.
This is probably because Mu was competing with an even scarier option: Delta. Delta was less experienced in avoiding antibodies than Mu, but it was more portable. “So, in the end, Delta spread more widely,” Dr. Bloom said.
The right option, the right time
Studying successful options tells only half the story. “The options that do not become dominant are, in a sense, negative controls,” said Dr Petrone. “They tell us what didn’t work and thus help fill in the gaps in knowledge about fitness.”
Delta is ahead of several options to avoid immunity in addition to Mu, including Beta, Gamma and Lambda. This model suggests that avoiding immunity alone was not enough to allow an option to surpass the highly transmitted version of the virus – or at least not during the early stages of the pandemic, when few people had immunity.
But vaccinations and numerous waves of infections have changed the immune landscape. The option with high immune protection should now have more advantage, scientists said, which is probably part of the reason why Omicron is so successful.
Another recent study suggests that in New York, the immune-avoiding Gamma range tends to perform better in neighborhoods with higher levels of existing immunity, in some cases because they were severely affected by the first wave of Covid. “We can’t look at a new version in a vacuum because it overshadows all the options that came before it,” said Dr. Wertheim, who authored the study.
In fact, the clash of past options reveals that success is highly contextual. For example, New York may be the birthplace of the Iota variant, which was first discovered in virus samples collected in November 2020. “And so it took hold in the beginning,” said Dr. Petrone. Even after the arrival of the more portable Alpha, Iota remained the dominant option in the city for months before eventually disappearing.
But in Connecticut, where both Iota and Alpha appeared in January 2021, things turned out differently. “The Alpha just took off right away and Iota didn’t stand a chance,” said Dr Petrone, who is leading a study of options in both regions.
A similar model is already being implemented with the numerous Omicron lines. In the United States, BA.2.12.1, a sub-option first identified in New York, began to develop, while in South Africa BA.4 and BA.5 caused a new leap.
That’s another reason to explore options that are dwindling, said Sarah Otto, an evolutionary biologist at the University of British Columbia. An option that has been poorly combined for a certain time and place may fly into another. In fact, His misfortune may simply be that he appeared too early. “There may not have been enough people with immunity to push this option,” Dr. Otto said.
But the next option for concern could be a descendant or something like an immune-avoiding line that has never been conquered, she said.
Looking back at previous versions can also give an idea of what worked – or didn’t – in retaining them. A new Gamma study provides further evidence that international travel bans, at least as applied by the United States, are unlikely to prevent the global spread of the option.
The range was first identified in Brazil in late 2020. In May of that year, the United States banned most non-US citizens from traveling to the country from Brazil, a restriction that remained in effect until November 2021. However, the range was opened in the United States. states states in January 2021 and soon spread to dozens of states.
Because Gamma has never dominated the world, the study of its distribution has given a “clearer” picture of the effectiveness of travel bans, said Tatiana Vasileva, a molecular epidemiologist at the University of California, San Diego and author of the study. “When it comes to exploring options like, say, Delta – something that has caused a big fire everywhere – it’s really hard sometimes to find models because it’s happening on a very large scale and very quickly,” she said. .
In an ongoing global health emergency, with a virus that is changing rapidly, there is an understandable impulse to focus on the future, said Dr. Fower. And when the world’s attention turned to Delta and then Omicron, he and his colleagues discussed whether to continue studying Mu’s old news.
“We were like, ‘Does anyone care about Him now?'” Dr. Fover recalled. “But we believe there is still room for high-quality research that asks questions about previous options for concern and tries to look back on what happened.”
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