The new cousin of the super-contagious omicron variant of the virus that causes COVID-19 hasn’t spread as fast as health officials had feared, raising hopes it won’t extend the devastating case surge that has filled hospital wards this winter.
The sub-lineage of the omicron variant known as BA.2 has been dubbed “stealth omicron” because it is harder to detect, and its rapid spread in other countries has worried health officials that it could overtake the dominant omicron strain and perhaps prove more virulent or vaccine resistant.
But Dr. Rochelle Walensky, director of the Centers for Disease Control and Prevention, said this week that does not appear to be the case.
“We’ve not seen any studies that suggest that it’s more severe,” Walensky said. “Nor have we seen studies that suggest that it will evade our vaccines any more so than omicron has already, and in fact, that our vaccines will work just like it has with omicron.”
Santa Clara County health officials announced Jan. 25 they had confirmed two cases of the BA.2 sub-variant. As of Wednesday, nine days later, that figure stood at 14.
Omicron quickly overtook the delta variant as the dominant U.S. strain, from less than 1% of cases nationally the first week of December when the first infections were confirmed to more than 99% today, and 98.5% in California. Omicron has four sub-lineages, of which BA.1 is the dominant strain.
Walensky said that as of this week BA.2 is about 1.5% of genetically sequenced cases in the U.S. Though the sub-lineage spread quickly in some other countries including Denmark, India and the United Kingdom, and is believed to be more transmissible than BA.1, it is not making a huge impact.
“What we know about BA.2 so far is that it does have a modest transmission advantage over BA.1,” Walensky said. “However, it’s not nearly the transmission advantage that we’ve seen between omicron and delta.”
The country that saw perhaps the greatest spread of BA.2 was Denmark. But Walensky noted that coincided with the country relaxing pandemic restrictions.
“In terms of how we anticipate this will impact cases, in many places we’ve seen BA.2 so far, cases have continued to come down, although at a slower rate,” Walensky said. “In some countries like Denmark, cases have gone up associated with BA.2, but that’s also in the context of relaxing mitigation strategies, mitigation measures, which is why we’re currently keeping those in place.”
Dr. George Rutherford, an infectious disease specialist at the University of California-San Francisco, said Thursday in a panel discussion that BA.2 has shown itself to be “somewhat more transmissible” than the BA.1 omicron virus. But they appear to produce the same viral loads in patients, and there’s “no evidence of increased clinical severity.”
Protection from booster shots appears to be the same with both BA.1 and BA.2 as well, Rutherford said.
Like Walensky, Rutherford said that the sub-lineage may only slow the decline in cases, which in California peaked January 12 and have been coming down ever since, according to data from the Institute for Health Metrics and Evaluation at the University of Washington, which runs a closely followed pandemic forecast.
“What’s the upshot of this? Well, if we have a lot of BA.2 that spreads and these kinds of data hold up that it’s somewhat more transmissible, we may have a longer tail on our decline,” Rutherford said. “If BA.2 starts to predominate, we may see a little bit longer tail, but aside from that I don’t think it’s going to have a lot of major impact.”
Some health experts however cautioned against complacency about BA.2. Epidemiologist Eric Feigl-Ding, a senior fellow at the Federation of American Scientists, noted the sub-variant has more than doubled in the United Kingdom over the last week, a concerning trajectory.
“The worrisome thing is that it’s rising despite so many who recently got omicron already and still it’s outcompeting it,” Feigl-Ding wrote Friday on Twitter.
The omicron-driven U.S. winter COVID-19 surge appears to have peaked in January and cases have been coming down since. Walensky said that the 446,400 cases per day across the U.S. represent a, 36% decrease from a week earlier, and the 17,100 hospitalizations are down 14%. COVID-19 deaths, at 2,300 a day, are up about 4%, she said.
“We are all cautiously optimistic as we see cases come down,” Walensky said. “Hospitalizations remain high. Daily deaths also remain quite high.”