The virus that causes COVID-19 didn’t change much in the early days of the pandemic. Then the number of mutations started increasing, and scientists began using an alphabet soup of letters and numbers to distinguish them.
But nothing prepared them for the dizzying array of strains that the mighty Omicron variant has been spitting out.
As one of the newest Omicron variants, BA.2.12.1, overtakes its predecessors, here’s what you need to know.
What is this BA.2.12.1 that is racing across the country?
First things, first. The original Omicron variant, called B.1.1.529, emerged in South Africa last year and spread quickly around the world. By late January, another Omicron subvariant, BA.1.1, already was dominant in the United States.
Fast forward to this spring. The BA.2.12.1 subvariant from the fast-moving Omicron lineage was first detected in New York in March, along with its sibling, BA.2.1. These two subvariants are estimated to spread 23 percent to 27 percent faster than their predecessor, the BA.2 variant. Consider that in early March, the Centers for Disease Control and Prevention reported that BA.2 accounted for about 26 percent of all cases in the US, and BA.2.12.1 accounted for less than 1 percent. By May 7, BA.2 had roughly doubled its prevalence, to about 56 percent of all cases — but BA.2.12.1 had exploded and now accounts for 43 percent of the country’s COVID cases. (It’s about 40 percent of New England cases, and the Broad Institute of MIT and Harvard estimates that it has taken over in Massachusetts, accounting for nearly 70 percent of cases.)
Will BA.2.12.1 elbow out its sibling for top spot?
Scientists tracking Omicron say that’s already happening. Yet its extraordinary speed, fueling another rapid rise in cases, is puzzling researchers because its structure is not all that different from its predecessor’s. “It’s almost like having somebody who runs a 2:30 marathon changing their sneakers and all of a sudden running a two-hour marathon. It doesn’t make sense,” said Dr. Jacob Lemieux, an infectious disease specialist at Massachusetts General Hospital, who is also coleader of the viral variants program at the Massachusetts Consortium on Pathogen Readiness.
Is BA.2.12.1 better at evading immunity?
Yes, it appears it has an increased capacity to evade antibodies triggered by a previous Omicron infection and vaccination, according to recent research by Chinese scientists that has not been peer reviewed. Dr. Pedro Piedra, a professor of molecular virology and microbiology at Baylor College of Medicine in Houston, compares these virus variants to a leopard that can change its spots to help it avoid detection.
“As these viruses go through the population once, it becomes harder to reinfect the population that already has a level of protection against that variant,” he said. “What we are seeing is these rapid changes that are enough for this variant to take a foothold and cause infection.”
What about the level of illness from BA.2.12.1?
While this latest subvariant doesn’t appear to be causing the flood of hospitalizations that the original Omicron wave did over the winter, hospitalizations are slowly rising again as cases mount in Massachusetts.
“I and many other people had expected that as treatments become more available, as vaccinations are more widespread, we would see a decoupling of the case counts and hospitalizations and we have to a large extent,” Lemieux said. “However it hasn’t been a complete decoupling that was hoped for. So we will have to keep a close eye on the hospitalization count.”
Are there yet more Omicron variants out there?
Yes. Meet BA.4 and BA.5, the newest offshoots identified by scientists in South Africa. The two subvariants have rapidly replaced Omicron’s BA.2 line, reaching more than 50 percent of sequenced cases in South Africa from the first week of April 2022 onward, a team of researchers there recently reported in a study that has not been peer reviewed. The scientists also reported “early signs” of rising hospital admissions in some of the country’s provinces. They said there are signs BA.4 and BA.5 may be even more wily about evading immunity. As far as causing more severe disease, they said the jury is still out.
Are BA.4 and BA.5 in the US?
Yes. Outbreak.info, a database that tracks variants worldwide, reports that BA.4 was first detected in the US in March, and has since been pinpointed in at least 17 states, including Massachusetts. But it still accounts for less than 1 percent of the samples sequenced in the country. According to the database, BA.5 has shown up in at least 13 states, including Massachusetts, as of mid-April, but it has a tiny presence here, accounting for fewer than 1 percent of sequenced samples.
Kay Lazar can be reached at email@example.com Follow her on Twitter @GlobeKayLazar.