In early 2021, scientists in Colombia found a worrisome new coronavirus variant. This variant, ultimately often called Mu, had a number of troubling mutations that specialists believed might assist it evade the immune system’s defenses.

Over the next months, Mu unfold swiftly in Colombia, fueling a brand new surge of Covid-19 circumstances. By the tip of August, it had been detected in dozens of nations, and the World Well being Group had designated it a “variant of curiosity.”

“Mu was beginning to make some noise globally,” stated Joseph Fauver, a genomic epidemiologist on the College of Nebraska Medical Heart and an creator of a current research on the variant.

After which it fizzled. At the moment, the variant has all however vanished.

For each Delta or Omicron there’s a Gamma, Iota or Mu, variants that drove native surges however by no means swept to international dominance. And whereas understanding Omicron stays a essential public well being precedence, there are classes to be realized from these lesser lineages, specialists say.

“This virus has no incentive to cease adapting and evolving,” stated Joel Wertheim, a molecular epidemiologist on the College of California San Diego. “And seeing the way it did that previously will assist us put together for what it’d do sooner or later.”

Research of the also-rans have make clear surveillance gaps and coverage blunders — offering extra proof that America’s worldwide journey bans weren’t efficient — and on what makes the virus profitable, suggesting that within the early part of the pandemic, transmissibility was extra necessary than immune evasion.

The analysis additionally highlights how a lot context issues; variants that make an impression in some locations by no means achieve a foothold in others. Because of this, predicting which variants will surge to dominance is troublesome, and staying on prime of future variants and pathogens would require complete, almost real-time surveillance.

“We will achieve so much by wanting on the viral genomic sequence and saying, ‘This one might be worse than one other one,’” Dr. Wertheim stated. “However the one method to actually know is to observe it unfold, as a result of there are a complete lot of doubtless harmful variants that by no means took maintain.”

Right here’s Mu

The coronavirus is consistently altering, and most new variants by no means get seen or named. However others elevate alarms, both as a result of they shortly change into extra widespread or as a result of their genomes look ominous.

Each had been true of Mu because it unfold in Colombia. “It contained a few mutations that individuals had been watching very intently,” stated Mary Petrone, a genomic epidemiologist on the College of Sydney and an creator of the brand new Mu paper. A number of of the mutations in its spike protein had been documented in different immune-evasive variants, together with Beta and Gamma.

Within the new research, which has not but been printed in a scientific journal, scientists in contrast Mu’s organic traits to these of Alpha, Beta, Delta, Gamma and the unique virus. Mu didn’t replicate quicker than another variant, they discovered, however it was essentially the most immune-evasive of the bunch — extra immune to antibodies than any identified variant in addition to Omicron, Dr. Fauver stated.

By analyzing the genomic sequences of Mu samples collected from everywhere in the world, the researchers reconstructed the variant’s unfold. They concluded that Mu had doubtless emerged in South America in mid-2020. It then circulated for months earlier than it was detected.

Genomic surveillance in lots of elements of South America was “patchy and incomplete,” stated Jesse Bloom, an professional in viral evolution on the Fred Hutchinson Most cancers Analysis Heart in Seattle. “If there had been higher surveillance in these areas, probably it might have been simpler to make a quicker evaluation of how fearful to be about Mu.”

Mu introduced one other problem, too. It occurred to have a sort of mutation, often called a frameshift mutation, that was uncommon in coronavirus samples. Such mutations had been flagged as errors when scientists, together with Dr. Fauver, tried to add their Mu sequences to GISAID, a global repository of viral genomes used to maintain tabs on new variants.

That complication created delays within the public sharing of Mu sequences. The time that elapsed between when a virus pattern was collected from a affected person and when it was made publicly out there on GISAID was persistently longer for Mu circumstances than for Delta circumstances, the researchers discovered.

“The genome itself was mainly creating synthetic surveillance gaps,” Dr. Fauver stated. “It resulted, at the very least in our expertise, in us not getting knowledge out for weeks when usually we’re attempting to get it out in days.”

(GISAID’s quality-control methods are necessary, the researchers harassed, and the repository has mounted the problem.)

Mix these surveillance gaps with Mu’s immune evasiveness and the variant appeared poised to take off. However that’s not what occurred. As a substitute, Mu radiated from South and Central America to different continents however didn’t flow into extensively as soon as it obtained there, the scientists discovered. “That was a sign that this variant was not as match essentially in possibly the North American and European populations as we had anticipated,” Dr. Petrone stated.

That was doubtless as a result of Mu discovered itself competing with an much more formidable variant: Delta. Delta was not as expert at dodging antibodies as Mu, however it was extra transmissible. “So, in the long run, Delta unfold extra extensively,” Dr. Bloom stated.

Proper variant, proper time

Finding out profitable variants tells solely half the story. “Variants that don’t change into dominant are, in a method, unfavorable controls,” Dr. Petrone stated. “They inform us what didn’t work, and, in doing so, assist to fill in information gaps round variant health.”

Delta overtook a number of immune-evasive variants in addition to Mu, together with Beta, Gamma and Lambda. This sample means that immune evasion alone was not sufficient to permit a variant to outdo a extremely transmissible model of the virus — or at the very least it wasn’t in the course of the early part of the pandemic, when few individuals had immunity.

However vaccinations and a number of waves of an infection have modified the immune panorama. A extremely immune-evasive variant ought to now have extra of an edge, scientists stated, which is probably going a part of the rationale Omicron has been so profitable.

One other current research steered that in New York Metropolis immune-evasive Gamma tended to do higher in neighborhoods with greater ranges of pre-existing immunity, in some circumstances as a result of they had been hit exhausting within the first Covid wave. “We will’t view a brand new variant in a vacuum, as a result of it comes about within the shadow of all the variants that got here earlier than it,” stated Dr. Wertheim, who was an creator of the research.

Certainly, the conflict of variants previous reveals that success is extremely depending on context. For instance, New York Metropolis might have been the birthplace of the Iota variant, which was first detected in virus samples collected in November 2020. “And so it obtained a foothold early on,” stated Dr. Petrone. Even after the extra transmissible Alpha variant arrived, Iota remained town’s dominant variant for months, earlier than ultimately fading away.

However in Connecticut, the place Iota and Alpha each appeared in January 2021, issues unfolded in another way. “Alpha simply type of took off instantly, and Iota didn’t stand an opportunity,” stated Dr. Petrone, who led a research of the variants within the two areas.

An analogous sample is already starting to play out with Omicron’s a number of lineages. In the USA, BA.2.12.1, a subvariant first recognized in New York, has taken off, whereas in South Africa, BA.4 and BA.5 are driving a brand new surge.

That’s one more reason to review variants that waned, stated Sarah Otto, an evolutionary biologist on the College of British Columbia. A variant that was poorly matched for a sure time and place might take off in one other. Certainly, Mu’s misfortune may need merely been that it emerged too quickly. “There won’t have been sufficient those that had immunity to essentially give that variant a lift,” Dr. Otto stated.

However the subsequent variant of concern may very well be a descendant of, or one thing much like, an immune-evasive lineage that by no means fairly took maintain, she stated.

Trying again at earlier variants also can present perception into what labored — or didn’t — in containing them. The brand new Gamma research, gives additional proof that worldwide journey bans, at the very least as the USA carried out them, are unlikely to forestall a variant’s international unfold.

Gamma was first recognized in Brazil in late 2020. In Might of that 12 months, the USA barred most non-U.S. residents from touring into the nation from Brazil, a restriction that remained in place till November 2021. But Gamma was detected in the USA in January 2021 and shortly unfold to dozens of states.

As a result of Gamma by no means got here to dominate worldwide, learning its unfold supplied a “cleaner” image of the effectiveness of journey bans, stated Tetyana Vasylyeva, a molecular epidemiologist on the College of California San Diego and an creator of the research. “In relation to learning variants like, let’s say, Delta — one thing that has brought about a serious outbreak in each place — it’s actually troublesome at instances to seek out patterns, as a result of it occurs on a really massive scale and really quick,” she stated.

In an ongoing international well being emergency, with a virus that adjustments quick, there may be an comprehensible impulse to concentrate on the long run, Dr. Fauver stated. And because the world’s consideration turned to Delta after which Omicron, he and his colleagues mentioned whether or not to proceed their research of old-news Mu.

“We had been like, ‘Does anybody care about Mu anymore?’” Dr. Fauver recalled. “However we expect there’s nonetheless room for high-quality research that ask questions on earlier variants of concern and attempt to look again on what occurred.”