A large spike in respiratory syncytial virus (RSV) and an earlier-than-expected arrival of the flu last year combined to create one giant respiratory mess—specifically, one of the worst flu seasons of the past decade.

The U.S. Centers for Disease Control and Prevention (CDC) reported between 27 million and 54 million cases of influenza nationwide last year, causing 300,000 to 650,000 hospitalizations and leading to up to 58,000 deaths.

One of the reasons last year’s flu season was so severe is because fewer people came down with the virus during the first two years of COVID-19—due to social distancing, masking and other preventive measures—leaving them more likely to get the flu once pandemic precautions ebbed.

That’s a big point infectious disease experts are making when they encourage everyone, including cancer patients, to get the flu vaccine as soon as it’s available this year.

“With mask mandates dropping, people becoming more lax with overcrowding and folks falling back to their pre-pandemic ways, there is a good possibility that we will see an uptick of RSV, COVID-19 and the flu,” says Suji Mathew, MD, Infectious Disease Physician and Chief of Medicine at City of Hope Atlanta.