A new form of the highly contagious omicron variant has been detected in Twin Cities wastewater but at low levels.
The subvariant, known as omicron BA.2, is 30-50% more infectious than its predecessor, but researchers are still trying to determine whether it is more severe.
It is also unclear whether it will evade immunity protection offered by previous COVID-19 illness, including for the many thousands of Minnesotans infected during the recent spike of omicron cases, and via vaccination.
The BA.2 subvariant has been found in most states, according to the Centers for Disease Control and Prevention, and accounts for nearly 4% of cases nationwide.
"We see that in the slightly rising case rate in the United States," said Dr. Rick Kennedy, co-head of the vaccine research unit at Mayo Clinic in Rochester. "We will see that continue to go up and we may even see a BA.2 spike like we had with omicron."
The BA.2 subvariant was first found shortly after the original omicron strain, known as BA.1, was discovered in late November. In some countries, such as South Africa, it has become the dominant strain.
"Some countries are seeing that spike but others are not," Kennedy said. "In some parts of the world, most of the cases in the country are BA.2, but hospitalization rates really haven't climbed up at all and the severity looks pretty similar to omicron."
However, in Denmark an outbreak of BA.2 has increased hospitalizations.
"They were just coming out of an omicron spike and thought they were out of the woods," Kennedy said.
The Metropolitan Wastewater Treatment Plant in St. Paul saw indications of BA.2 a few weeks ago as part of its ongoing analysis of COVID-19 trends conducted in partnership with the University of Minnesota Genomics Center.
Last week, researchers found BA.2 was present in 4.4% of samples for the week ending Feb. 14, up from 1.6% the previous week.
The plant treats wastewater for 1.95 million metro area residents, including Minneapolis, St. Paul and more than 60 suburbs. Wastewater analysis is a good predictor of COVID-19 trends because the genetic material of the virus shows up in sewage before people seek testing, which usually comes after they develop symptoms.
So far, overall COVID-19 in Twin Cities wastewater is still going down despite the appearance of BA.2.
"All of the indications are since the first week of January it has been going down, down, down very quickly and much more rapidly than many of the other waves that we have seen," said Steve Balogh, a principal research scientist at the Metropolitan Council.
Minnesota's case numbers and trends bear that out.
Another 4,050 new COVID-19 infections were announced Wednesday by the Minnesota Department of Health. Because of reporting delays caused by the Presidents' Day holiday, the number represents four days of test results delivered to the health agency since 4 a.m. Saturday.
Minnesota's testing positivity rate has fallen to 7.5%, the lowest since last October.
Hospitalizations continue to decline, with 622 COVID-19 patients in the state's hospitals, including 98 requiring intensive care.
Another 26 COVID-19 deaths were announced Wednesday, bringing the number of fatalities to 12,019. There have been more than 1.4 million COVID-19 infections in Minnesota detected by testing.
Through genetic analysis of testing samples, Minnesota has found 55 cases of the BA.2 variant in the month that ended Feb. 12. That accounts for 0.5% of the state's omicron cases to date. One person with the BA.2 subvariant was hospitalized but there have been no deaths among the other known BA.2 cases, agency spokesman Doug Schultz said.
The Metropolitan Council is scheduled to release updated BA.2 prevalence data Friday.
Scientists are still studying the subvariant to better understand its transmissibility, severity and ability to evade immunity.
"Reinfection with BA.2 following infection with BA.1 has been documented," the World Health Organization said in a statement Tuesday. "However, initial data from population-level reinfection studies suggest that infection with BA.1 provides strong protection against reinfection with BA.2, at least for the limited period for which data are available."
As the virus that causes COVID-19 continues to mutate, it has tended to become more infectious, which helps it crowd out other variants, Kennedy said. But more needs to be learned about whether BA.2 resembles the original omicron in terms of disease severity.
"I'm sure we will start to get more information from other parts of the world where most of the cases are now BA.2," Kennedy said. "In the next coming weeks we will have a clearer picture."
