Influenza, respiratory syncytial virus (RSV), and COVID-19 are all part of the seasonal respiratory virus lineup. According to the Centers for Disease Control and Prevention (CDC), the upcoming fall and winter are expected to have a similar number of hospitalizations for respiratory diseases as last year. However, they say it's important to note that these hospitalization numbers are higher than before the COVID-19 pandemic when the leading causes were the flu and RSV.

Matthew Binnicker, Ph.D., director of the Clinical Virology Laboratory at Mayo Clinic, says researchers in the Northern Hemisphere look to the trends in the Southern Hemisphere, where winter is ending, to help forecast the upcoming respiratory season.

Watch: Dr. Matthew Binnicker talks about the upcoming 2023-2024 respiratory season

Journalists: Broadcast-quality soundbites are available in the downloads at the bottom of the posts. Please courtesy: "Matthew Binnicker, Ph.D./Laboratory Medicine and Pathology/Mayo Clinic."

"We saw in Australia that they had a typical to, in some areas, more severe influenza season. And that's what I expect this year is more of what we saw pre-pandemic," says Dr. Binnicker.

"Whether it's an average year or a more severe year will be based on a few factors: how well people abide by all the lessons we learned about staying home when you're sick, masking if you're sick, getting your influenza vaccination, but also the type of virus that's circulating," he says.

The CDC says the 2023 Southern Hemisphere flu vaccine reduced hospitalizations by 52%. If similar influenza virus strains spread in the Northern Hemisphere, the 2023-24 vaccine might provide equal protection.

Strains of influenza

Dr. Binnicker says there has been a predominance of a few different strains of influenza over the last few years.

"One is called H3N2 influenza A virus, a common influenza A virus that circulated for years. And then, in some areas, the pandemic strain from 2009, the H1N1 influenza strain, has also been in circulation. We typically see those influenza A strains anywhere from November to February or March here in the U.S.," says Dr. Binnicker.

"We also see a strain of influenza called influenza B, which usually causes a little bit less severe disease, and that typically comes up toward the tail end of the influenza season, in the February, March and April timeframe," he adds.

Preventing illness during respiratory season

There are some unknowns in the outlook, including the timing, the specific virus strains and what new COVID-19 variant might emerge. That's why prevention is critical, says Dr. Binnicker.

The good news is that there are vaccines for these three seasonal illnesses, including updated COVID-19 vaccines and new vaccines for the prevention of RSV in those 60 and older, infants and those who are pregnant.

"It's an exciting time in terms of prevention strategies for these viruses," says Dr. Binnicker. "Then you get to the basics: good hand hygiene. If you're sick, stay home. If you have to get out, wear a mask if you have any of these symptoms. And then testing so we know what we're dealing with and can take good steps to prevent transmission to other people.”

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