Virus World

'Only having a transmissibility advantage at this stage of the game isn't a total showstopper'.  The Omicron sublineage BA.2 is making headlines for its potentially increased transmissibility as its prevalence rises in some countries, but experts aren't too concerned about the variant just yet. Late last week, the U.K. Health Security Agency designated BA.2 a "variant under investigation" as cases were doubling every 4 days and showing a 120% growth advantage over the original Omicron clade, known as BA.1, said Katelyn Jetelina, PhD, MPH, an epidemiologist at UT Health Science Center at Houston.  Other countries, including Denmark, Norway, Sweden, and India, have seen similar growth for BA.2, Jetelina reported in her Substack email. Still, she said, it's "likely nothing like the huge transmissibility jump we saw from Delta to Omicron," which was a 500% growth advantage. So far some 8,000 cases of BA.2 have been detected in 40 countries, according to news reports. BA.2 is not a new sublineage. It was first detected in December and made headlines then as the "stealth" Omicron variant because it did not have the same s-gene target failure on PCR testing that BA.1 did. That's because it lacks the spike deletions 69-70 in BA.1, so s-gene targets still turn up positive. That means BA.2 doesn't have a special signal that tells labs it's Omicron, so labs now must go to genetic sequencing to identify variants, Jetelina said. She added that while it has many of the same mutations as BA.1, it has a lot of differences too. While BA.1 had about 60 mutations, BA.2 has about 85 mutations.

 

While it appears to have a transmission advantage, it's not clear what the additional mutations mean for severity, immune evasion, and other parameters. "It may have a slight growth advantage but [there's] no evidence at all yet that it can evade Omicron (BA.1) immunity or be different to Omicron in any meaningful way," tweeted Meaghan Kall, a PhD student at the U.K.'s Health Security Agency. "Variants will continue to emerge, but not all variants will be a problem." She noted that while the growth advantage for BA.2 looks "more than slight," it's still "too early to say with so few samples. This happens every time a variant emerges first couple weeks, some sort of founder effect. I'll trust growth estimates next week more."  "Only having a transmissibility advantage at this stage of the game (with population immunity so high) isn't a total showstopper," Kall added. In Denmark, BA.2 now accounts for nearly half of all cases detected there. Early data, however, indicate that it has not been associated with an increase in hospitalizations there. Health authorities there also said there's likely to be a minimal difference in vaccine effectiveness between BA.1 and BA.2. Norway reported a rapid increase in BA.2 infections, rising from seven cases detected on Jan. 4 to 611 cases detected on Jan. 19, the majority occurring in Oslo. Norwegian authorities also concurred that BA.2 is likely more contagious than BA.1. Still, there are no data yet on the key question of whether those who were infected with the "original" Omicron can get re-infected with BA.2. Omicron is not the first variant to have a "plus" version. Last year, the Delta Plus variant made headlines, but never gained much ground over the original Delta variant.