The latest Minnesota wastewater sampling is showing a decline in COVID-19 levels, defying a pattern of fall increases over the last three years.

Coronavirus levels in wastewater have remained low for months, but were nonetheless increasing in Minnesota until they started to decline again in late September, according to an update Friday of the University of Minnesota’s monitoring dashboard.

The rise and fall suggests that human behavior can still influence COVID, even when it is no longer at pandemic levels, said Timothy Schacker, vice dean for research at the U of M Medical School.

The late summer increase “correlates with a lot of things — the State Fair, high school sports, school going back in session,” he said. “We did see across the state a measurable uptick in the amount that is in the wastewater” before the decline.

Wastewater monitoring is a sensitive indicator of changes in viral levels in the community. The U is planning later this year to offer monitoring for influenza and RSV as well, Schacker said.

Upticks in viral spread were followed consistently during the pandemic with increases in COVID-19 hospitalizations two weeks later and deaths two weeks after that. The pattern is holding this fall, with the 241 COVID-19 hospitalizations on Tuesday being the highest total since April 3, according to Thursday’s state update.

COVID-19 deaths have increased to three per day, raising Minnesota’s total to 15,067. September’s 72 deaths — almost all in the elderly — represented the highest monthly total since May. The state by comparison recorded 1,808 COVID-19 deaths in December 2020, before vaccine was widely available.

The recent dip in viral spread buys time for continued rollout of the new COVID-19 vaccine, which was based on the XBB.1.5 coronavirus variant that was dominant in Minnesota until mid-summer. Studies indicate the new vaccine still protects against severe illness from the most recent variants.

Some Minnesota clinics and pharmacies reported limited supplies of the vaccine when it became available last month. Only about 265,000 Minnesotans, or 4.8% of the population, are up to date with current COVID vaccine recommendations.