On Tuesday, 11 instances of the strain, called BA.2, were reported in California, just two days after the first cases of an offshoot of the more transmissible Omicron form were detected in the United States. According to several accounts, two of these cases were discovered in Santa Clara County, one of the state's most populous counties.
It's still early, but based on the rate of spread in nations like Denmark and the United Kingdom, several scientists believe BA.2 will be at least slightly more transmissible than Omicron (BA.1).
“The consistency of BA.2 growth across several counties means that it’s more transmissible than BA.1,” wrote epidemiologist Dr. Katelyn Jetelina of the University of Texas Health Science Center at Houston on Tuesday. “It’s likely nothing like the huge transmissibility jump we saw from Delta to Omicron,” however.
BA.2 has wreaked havoc on Denmark the most. It was responsible for approximately half of the test samples sequenced in that country as of Monday. According to data from Statens Serum Institut under the aegis of the Danish Ministry of Health, the subvariant accounted for 20% of all Covid cases in Denmark in the final week of December. According to GISAID data, BA.2 was responsible for more than 60% of cases in that country by today.
That means, according to Dr. Jetelina, the new Omicron variety appears to be out-competing the original in Denmark, just as that variant out-competed Delta.
The label "stealth" was given to the offshoot because officials believe it will be more difficult to distinguish from other varieties than the original Omicron, not because it will elude present testing procedures. In PCR tests, BA.2 does not show a telltale indication that commonly shows Omicron. While a PCR test would still yield a general positive result, genome sequencing — a far more expensive and time-consuming method that is less prevalent — would be required to identify the exact variation involved.
On Monday, the first cases of BA.2 in the United States were reported in Washington State. At least three cases have been discovered at Houston's Methodist Hospital, which has more robust genomic sequencing than other hospitals.
The Omicron branch is also affecting the United Kingdom, Norway, France, India, Sweden, and dozens of other countries.
“New variants will continue to evolve as long as there are large pockets of unvaccinated people,” the California Department of Public Health observed in a statement to the Mercury News. “Strengthening our protection against Covid-19 through vaccination and boosting is more important than ever.”
