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.
"If you've been exposed or you have symptoms and you test negative," he said, "it doesn't necessarily mean you are in the clear with regards to COVID infection. You may need to perform a follow-up test in a few days."
Minnesota on Tuesday offered to mail four free at-home tests to the first 250,000 households that request them, providing capacity for initial and follow-up tests. As of Friday, 65,000 households had requested them at https://mn.gov/covid19/get-tested/at-home/index.jsp.
The state on Friday reported another 546 coronavirus infections and two COVID-19 deaths, bringing the state's death toll in the pandemic to 12,410. However, COVID-19 hospitalizations declined from 1,629 on Jan. 14 to 189 on Thursday.
Patients requiring intensive care also declined during the omicron wave, indicating that the variant produces a lower proportion of severe illness. The 26 ICU cases on Thursday were a decline from 374 on Dec. 16, when the more-severe delta variant was responsible for most hospitalizations.
Immunity levels from recent infections and vaccinations could impact the timing and severity of future COVID-19 activity. Only 48.9% of Minnesotans 5 and older are considered up to date with COVID-19 vaccinations, either because they completed the initial series recently or received booster doses after earlier shots.
However, the stunning number of COVID-19 cases in Minnesota during the omicron wave produced some level of temporary immunity as well. Minnesota has identified more than 1.4 million infections in the pandemic, and nearly 30% occurred in 2022 — not including the results of at-home tests that aren't reported publicly.
The Institute for Health Metrics and Evaluation in Washington state estimates that around 70% of Minnesotans have some level of COVID-19 immunity right now, but that this protective rate will decline this spring.
