See more of the story

Unclear predictors of the approaching cold and flu season have Minnesota leaders urging precautions and promoting vaccination.

Gov. Tim Walz received his flu shot Wednesday and encouraged others to seek it along with any recommended vaccination against COVID-19. He received his second COVID-19 booster in a public event earlier this month.

"Now is about the time in Minnesota," Walz said before receiving his shot in a public event at the State Capitol.

Influenza caused 1,500 to 6,200 hospitalizations per season in Minnesota in the five years before the pandemic, but it has been an afterthought since the emergence in March 2020 of the coronavirus that causes COVID-19. Only 35 flu-related hospitalizations were reported between October 2020 and May 2021, which is the typical span of the influenza season. The state reported 917 flu-related hospitalizations last season.

Health officials believe precautions such as mask-wearing and social distancing helped reduce influenza during the last two winters, but people aren't using them as frequently anymore.

On the optimistic side, flu activity has been mild in the Southern Hemisphere — other than isolated upticks in Australia and other locations, said Michael Osterholm, director of the University of Minnesota's Center for Infectious Disease Research and Policy.

That could mean a mild flu season as the virus creeps northward. On the other hand, the lack of exposure to influenza over the last two years could leave Minnesotans susceptible.

The severity of the flu season "is going to be somewhere between a one and a 10," Osterholm said.

The pandemic disrupted historical patterns, but some infectious diseases are returning to expected transmission levels.

Respiratory syncytial virus (RSV) typically infects infants in the winter, but caused a spike in pediatric hospitalizations in summer 2021. RSV-related hospitalizations increased to 30 in the Twin Cities area in the week ending Sept. 17, suggesting a typical seasonal increase ahead, according to the state Department of Health.

"Cold bugs are increasing like usual," said department spokesman Doug Schultz.

Norovirus-related stomach illnesses dropped well below historical averages in 2020 and 2021, but surged late this winter, according to new data from Minnesota and 11 other states.

The effectiveness of the flu vaccine depends partly on how well it is matched to the circulating strains of influenza. Bloomington-based HealthPartners has contributed to research showing a range of effectiveness, which was 35% last season but had been as high as 60% in the 2010-2011 flu season.

Uptake also will play a role. Health officials are concerned that hesitancy over the relatively new COVID-19 vaccines will reduce interest in the tried-and-true flu vaccines.

A study published this summer in the New England Journal of Medicine showed that states with low COVID-19 vaccination rates also tended to have declining flu vaccination rates. However, Minnesota's use of flu vaccine changed very little before and after the pandemic.