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Disease Modeling By University of Pittsburgh Warns Of “Twindemic”

Robert Pfeil

This year’s flu season could be particularly severe, which presents concerning implications for medical systems due to the ongoing surge of COVID-19 illness.

Last year, public health officials warned of a possible so-called “twindemic” where hospitals would be simultaneously slammed with significant numbers of both flu and COVID-19 patients. That didn’t happen due to effective coronavirus mitigations like face masks and physical distancing, which suppressed the circulation of all viruses, including influenza.

In fact, during the most recent flu season, the Centers for Disease Control and Prevention reported just one pediatric death in the entire U.S. During the previous year at least 195 children died from influenza.

But now, health systems, including pediatric hospitals, are already seeing a rise of respiratory illnesses such as RSV. And with fall just around the corner and at least 38% of the U.S. public still unvaccinated, a twindemic appears more likely. Statistical modelling from the University of Pittsburgh also suggests this, predicting there will be as many as 400,000 extra flu hospitalizations this season, amounting to a 20% increase.

“Much of the immunity that we have as a population occurs because people in a population had influenza last year,” said Dr. Mark Roberts, director of the University of Pittsburgh’s Public Health Dynamics Laboratory.

In other words, the “residual immunity” that a population usually carries over from a previous flu season will not be as strong, because fewer people got sick last year.

Roberts noted that his lab used two “completely different” modeling methodologies that gave “surprisingly similar results” to suggest a bad flu season is coming.

“We normally have hundreds of thousands of people who get admitted to the hospital with influenza. And if that happens on top of the current Covid pandemic, there is a tremendous chance that some of these hospitals will be stretched beyond their breaking point,” said Roberts.

When asked how he thought hospitals in the Pittsburgh region would fare, Roberts noted that so far, Allegheny County is doing a better job than many parts of the county at preventing the spread the delta variant as evidenced by the region's moderate number of COVID-19 hospitalizations.

Like other public health experts, such as the director of Allegheny County’s health department, Roberts is urging people to get this year’s flu vaccine. While the vaccine is not 100% effective, like the COVID-19 vaccine, it can reduce the risk of severe illness.

Sarah Boden covers health and science for 90.5 WESA. Before coming to Pittsburgh in November 2017, she was a reporter for Iowa Public Radio. As a contributor to the NPR-Kaiser Health News Member Station Reporting Project on Health Care in the States, Sarah's print and audio reporting frequently appears on NPR and KFF Health News.