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Record-setting flu season comes to an end

At 22 weeks, this was the longest above-baseline flu season in at least 20 years of CDC records.

The official end to the 2019-20 flu season doesn't bring relief - or even a sense of finality - thanks to the worldwide COVID-19 pandemic. The flu season's end actually brings some concern from infectious disease experts who worry about a rise in COVID-19 cases as parts of the United States ease isolation measures.

As for the flu, visits to healthcare providers for flu-like illnesses fell to 2.2 percent, which is below the national baseline of 2.4 percent for the first time since Nov. 16, 2019, when it was 2.5 percent. At 22 weeks, it was the longest above-baseline flu season in at least 20 years of Centers for Disease Control and Prevention (CDC) records. Last year was the previous longest at 20 weeks.

A total of 19,932 laboratory-confirmed influenza-associated hospitalizations were reported between Oct. 1, 2019, and April 18, 2020, according to the CDC. That's the second-highest total - there were 30,453 in 2017-18 - since such figures were first kept during the 2009-10 flu season.

Credit: AccuWeather
A weekly report of reported flu illnesses in 2020.

COVID-19 cases caused disruptions in the collection of influenza-like illness (ILI) data, however, as the CDC noted in its report. "The COVID-19 pandemic is affecting healthcare-seeking behavior," the report documented. "The number of persons and their reasons for seeking care in the outpatient and emergency department settings is changing. These changes impact data from ILINet in ways that are difficult to differentiate from changes in illness levels. ILINet data should be interpreted with caution."

What concerns infectious disease experts is what's ahead.

"COVID-19 cases will continue to mount and the rate of growth, which has recently leveled off, may again increase as social distancing measures become increasingly relaxed," Dr. Bryan Lewis, a professor at the Biocomplexity Institute at the University of Virginia, told AccuWeather.

"There is little sign that these deaths will stop at this rate for a few more weeks," Dr. Lewis added. "More importantly, it seems this disease will be around for some time and continue to bring significant morbidity and mortality."

The possible combination of COVID-19 and next year's flu season is on the minds of some experts. Flu season typically begins in October, peaks between December and February and lasts well into March, although activity can last as late as May. Flu viruses are more stable in cold air and the low humidity allows the virus particles to remain in the air, according to Peter Palese, who was the lead author on a key flu study in 2007.

A report recently sent to the White House by a panel of experts studying the impact of higher temperatures and high humidity on the spread of COVID-19 determined "it's inconclusive scientifically," according to the chair of the panel, Dr. Harvey Fineberg. He suggested to AccuWeather that because the virus is so new, the science is far from being settled.

However, he added, "It's pretty clear that when you look at this virus in the laboratory, if you raise the temperature and you raise the humidity, the virus does not do as well," he told AccuWeather.

The Biocomplexity Institute's Dr. Lewis would like to see that play out as summer nears. "There is still hope more temperate weather may moderate COVID-19 transmission rates, and perhaps provide a boost to relaxed social distancing measures that are going into effect in the coming weeks," Dr. Lewis told AccuWeather.

"Regardless of the impact of the milder weather this summer, it is likely that as we enter flu season this fall, concerns about COVID-19 and influenza will both be heightened," he added. "A weary populace may be extra concerned and hopefully amenable to advice about a disease [influenza] for which we have proven treatments and vaccines."