Pandemic activity remains low in Minnesota, but a concerning BA.2 subvariant of the coronavirus is now the dominant source of COVID-19 in the state.
Sampling at the Metropolitan Wastewater Treatment Plant in St. Paul over the past week found that BA.2 made up 72% of the viral load in Twin Cities sewage. The total viral load increased 53%, but it remains at far lower levels than earlier this winter during the delta and omicron COVID-19 waves.
Friday's updated wastewater data revealed the rising presence of a strain responsible for surges in COVID-19 activity in Europe last month. The positivity rate of COVID-19 testing dropped from 23.4% in mid-January to 2.7% last month in Minnesota, but it nudged to 2.9% in the week ending March 24 when BA.2 became predominant.
"We will see an increase in cases in many parts of the United States, but it's not thought to result in a large surge like we experienced in January or early February of this year," said Matthew Binnicker, director of clinical virology at Mayo Clinic in Rochester.
Qualities of the BA.2 variant itself will fuel some spread, including its rapid transmission and heightened ability to evade immunity compared with earlier strains. However, Binnicker said BA.2 and earlier forms of the omicron variant have been tagged with overly dramatic labels, such as "stealth" variants.
"Stealth variant really implies that it's going undetected, that we're missing it," he said. "It was wrongly given that name ... The PCR tests and the antigen tests are still able to pick up BA.2, similar to BA.1 and all of the other prior COVID variants."
The label emerged because one component within standard COVID-19 diagnostic testing failed to identify coronavirus infections involving omicron. However, that deficiency ended up as a preliminary clue that infections involved the variant.
Binnicker said there is concern with BA.2 infections because of the slower buildup of virus in the nasal cavity, which could fool tests performed early in the course of illness or viral exposure. Positives appear to come faster with PCR tests compared to the rapid at-home antigen tests that are gaining popularity, he added.