Tridemic? Minnesota doctors worry about flu season on top of pandemic

A peak in the latest COVID-19 wave could come next month, as some models have predicted, but Minnesota hospital leaders are preparing for a winter in which the lingering pandemic combines with other respiratory viruses to spawn a miserable flu season.

Minnesota was spared a much-hyped "twindemic" of COVID-19 and influenza last winter because of mask-wearing and closure orders that limited person-to-person contact, but an unprecedented summer surge of respiratory syncytial virus, or RSV, shows what can happen without those protections, said Dr. Gregory Poland, a vaccinologist at Mayo Clinic in Rochester.

"I'm not going to talk about a twindemic. I'm going to talk about a tridemic or a quaddemic," he said. "We've already seen evidence of it. We already have cases of influenza in Minnesota. We've already seen evidence of an RSV epidemic. The pandemic, at least right now, isn't going anywhere. It's going to continue to find susceptibles who are either unvaccinated or whose immunity wanes with time."

Predictions about influenza vary. The mild flu season in the Southern Hemisphere this summer suggests a mild U.S. season this winter. On the other hand, the absence of influenza last winter could leave people more susceptible. Health officials said they at least need to prepare for a severe season and urged people to seek vaccinations against influenza and COVID-19 — including newly recommended booster doses for some vulnerable groups.

"It is concerning to think about even a 'normal' flu season layered on top of what we are currently seeing with COVID-19, let alone a severe season," said Kris Ehresmann, state infectious disease director, in a statement. "Our health care system is stressed right now due to COVID-19."

Pandemic models by Mayo Clinic and the Centers for Disease Control and Prevention predict modest increases or declines in COVID-19 levels in early October in Minnesota, which could follow states such as Missouri, which had severe surges earlier this summer that have since peaked.

Minnesota on Monday reported a 6.9% positivity rate of COVID-19 testing, which is above the state's 5% caution threshold for viral spread but below a high of 7.1% last week. COVID-19 hospitalizations also declined from 794 on Tuesday to 755 on Friday.

The surge in hospitalizations is being followed by more COVID-19 deaths. The state reported 22 COVID-19 deaths on Monday, raising its toll in the pandemic to 8,098. Monday's report included a 30- to 34-year-old Hennepin County resident — the state's 44th death in the pandemic involving someone younger than 35.

The pandemic has upset seasonal illness patterns, including last winter's flu season. Poland said the total U.S. flu cases last season equaled the number seen on single days in other seasons.

In Minnesota, 35 influenza hospitalizations were reported in the past season — compared with a range of 1,538 to 6,446 in the previous five seasons.

Doctors said this summer's RSV surge has been unprecedented, combining with COVID-19 to clog the Minneapolis and St. Paul emergency departments of Children's Minnesota. Children's reported 210 RSV infections last week — at a late summer period when it usually would expect none.

RSV is a common cause of colds that can be more severe in preschool children and presents a risk, in combination with influenza and COVID-19, if it is widespread, said Dr. Marc Gorelick, chief executive of Children's Minnesota.

"If everybody gets it, and even only a small percent gets really sick, that's still a lot of kids," he said.

Forecasting any of these viruses is challenging and involves many more factors than are included in the current predictive models, said Michael Osterholm, director of the University of Minnesota's Center for Infectious Disease Research and Policy.

A popular theory is that RSV spread after people stopped taking precautions. The rate of Minnesotans wearing masks in public most or all the time declined from more than 60% in May, when a state mandate was in effect, to less than 20% in July. The rate has since increased to 46%, according to COVIDcast survey data.

However, Osterholm noted that RSV has uncharacteristically surged in some countries that did not have mask requirements or other mitigation measures in place.

Models also aren't able to account for this summer's unpredictable pattern of COVID-19, which he said spread like "viral lava" in some states but hasn't yet surged in New York City or Los Angeles.

Osterholm said he predicts that COVID-19 will remain a problem in the U.S. this winter, even if there is a decline from peak infection rates. Minnesota's first-dose COVID-19 vaccination rate is 74.6% among eligible people 12 and older, and 63.4% overall, leaving opportunities for the virus to spread.

"We still have a lot of human wood to burn here," Osterholm said.

Concerns remain about the fast-spreading delta variant of the coronavirus infecting fully vaccinated people.

Minnesota on Monday reported 4,717 breakthrough infections that were identified in the past week. That makes up 30% of the 15,896 coronavirus infections identified in the past week — although breakthrough and total cases aren't reported in the same way.

In total, Minnesota has identified 28,047 breakthrough infections — or 0.9% of the state's more than 3.1 million fully vaccinated people.

Federal officials last week advised third booster doses of the Pfizer COVID-19 vaccine based on concerns of waning immunity after the first two doses. Recommendations regarding the Moderna and Johnson & Johnson vaccines are pending.

Following federal guidance, the state told providers on Friday that they should give Pfizer boosters to people 65 and older, and to people 50 to 64 with underlying medical conditions.

Providers can consider giving boosters to people 18 to 49 with underlying medical conditions and people 18 to 64 at increased risk of workplace exposure to the virus.

Poland said people should take advantage of the fact that flu and COVID-19 vaccines can be given at the same time, preferably in separate arms to assign any side effects.

"You can go and at the same time get both vaccines," he said. "I hope that people will."