In recent weeks, there have been frequent reports of the rise of the more transmissible Omicron subvariant BA.2 around the world. BA.2 now makes up almost all the new cases in Denmark, the UK, Switzerland, Sweden, India, Belgium, Norway, South Africa, The Philippines, Hong Kong and many more regions.
Throughout the first few weeks of the year, however, as it spread rapidly abroad, BA.2 did not see significant growth in the United States. No longer.
In the second and third weeks of March, the percentage of new US cases sequenced that were attributed to BA.2 was nearly 1 in 4, or 23%. That, per data from Covariants.org, which pulls worldwide data on the genomically-sequenced samples submitted to the GISAID data-sharing hub. In fact, since late January, identified cases of BA.2 have doubled (and sometimes tripled) every two weeks in the US
The first identified cases of BA.2 in the United States appeared at roughly the same time as they did in the UK and Denmark: late November & early December 2021. But from that period through mid February, BA.2 made a little headway in the US, accounting for just 3% of all sequenced cases in the country by the 21st, per Covariants.org.
But during the same timeframe, the percentage of sequences attributable to BA.2 in the UK grew to 34%. By February 21 in Denmark, the variant’s conquest was nearly complete; It accounted for 95% of all sequences.
A late January report from the Statens Serum Institute, which operates under the auspices of the Danish Ministry of Health, found that “BA.2 may be approx. 30% more transmissible than BA.1 (the original Omicron). ” Some analyzes since then have claimed the variant’s transmissibility advantage is even higher.
The good news is that the Omicron strains are much less virulent than the Delta, but as the US saw in early February of this year, Omicron’s increased transmissibility can create a wave of deaths equal to or surpassing that of the Delta by the sheer number of infections alone .
Ominously, there may be indications of a new wave in cases in some nations where BA.2 is dominant.
The 7-day average number of new cases in the UK has more than doubled from a recent low of about 27,000 on February 24 to more than 61,000 on March 14, per Johns Hopkins. The same average in Denmark, however, has fallen from more than 24,000 to 8,800 in the same time period. And the US has shown no according to rise in new cases, even as its share of BA.2 has grown.
The reasons for the differences in rates of spread among countries are unclear. “The difference in growth potential between countries may be linked to differences in vaccination coverage and contact patterns arising because of restrictions, population densities, etc.,” a WHO report suggested.
Denmark and the UK lifted restrictions earlier than the US, but their citizens are more highly vaccinated than Americans. Yet the US has not experienced the kind of BA.2 growth those European countries, even as we’ve also broadly lifted masking and other restrictions.
As for population density, the UK is overall far more concentrated than Denmark, which itself is denser than the United States – which, of course, does have its own highly dense urban centers.
Muddying the analysis is that testing is way down in the US Also on the way down are the number of tests getting sequenced – a pricey process. The number of sequences in the US dropped from about 25,000 on March 7 to about 200 on March 14. And visibility into trends might get even worse.
The White House told NPR today that the program that pays to test, treat and vaccinate people who don’t have health insurance will be winding down after Congress declined to add funding to a larger spending bill last week.
The Biden administration warned lawmakers this week that, as a result, the country risks being “blindsided” by future variants.