“We are seeing an increase in the proportion of BA.2 that is detected,” warned the World Health Organization’s technical lead on Covid-19, Dr. Maria Van Kerkhove. “Of the sequences that are available, about 75% are BA.2 and 25% of those are BA.1,” which is the original Omicron strain.
Just one month ago, WHO released a report on BA.2 that showed the strain accounted for 21.5% of all new Omicron cases analyzed worldwide in the first week of February. That means in one month, it’s grown more than 2X, displacing BA.1 as is did so.
“Studies have shown that BA.2 has a growth advantage over BA.1,” according to a WHO analysis, possibly because it lodges higher in the respiratory tract, and so infection can result from lighter exposures. The “difference in transmissibility appears to be much smaller than, for example, the difference between BA.1 and Delta,” says the WHO report, but it is an advantage.
In the U.S., where BA.2 has been a non-factor up until now, sequences of the variant have doubled each of the past few weeks, and it now accounts for 23% of all positive tests sequenced.
What’s more, the rise in BA.2 cases is happening across the U.S. According to CDC data, the variant now accounts for 27% of all sequences in California, Arizona and Nevada (California, it should be noted, does not differentiate between BA.1 and BA.2 in state data accessible to the public). In the Southeast, it’s only 12%, while in the Northeast, it’s above 38%.
The Washington Post reports that “about a dozen nations are seeing spikes in coronavirus infections caused by BA.2,” specifically in Western Europe and even more specifically in Germany, which saw its highest ever 7-day average case count yesterday. The increase in cases is raising concerns about another wave stateside. Despite an overall continuing decline in cases here, U.S. Covid waves have often followed those in Europe by 2-3 weeks.
“However, the amount of testing that is happening worldwide is dropping substantially,” said WHO’s Dr. Van Kerkhove. “So our ability to track this virus, our ability to track BA.2 is compromised because testing is reduced, and you can’t sequence those who you don’t test.”
But a Bloomberg analysis of CDC wastewater data may provide better insight. It found about 33% of U.S. sites monitored showed a rise in Covid levels from March 1-10. That’s double what it was during the same period in February.
Wastewater is often the earliest — and most accurate — indicator of a coming surge because it does not rely on people deciding to take tests, and it covers the entire population serviced by each sewage system. Rising case numbers usually follow rising wastewater data after a few weeks.
“While wastewater levels are generally very low across the board, we are seeing an uptick of sites reporting an increase,” Amy Kirby, who heads the CDC’s wastewater monitoring program, said in a statement. “These bumps may simply reflect minor increase from very low levels to still low levels.”
But wastewater by no means provides a complete dataset. Many parts of the country do not analyze wastewater for Covid-19. That could be part of a larger problem if, indeed, there is a coming wave Stateside.
“We need a very strong surveillance system around the world for Covid-19,” said Dr. Van Kerkhove this week. “Despite all of the challenges we are facing, we still need to maintain testing. We still need to maintain robust sequencing and making sure that we have good geographic representation of the sequences that are shared so that we can really track this virus in real time.”