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Experts are warning about a potential “tridemic” of illnesses this winter. Paulo Sousa/EyeEm/Getty Images

Health officials are reporting that this year’s flu season in the United States is off to a strong start.

They say flu cases are reportedly high in at least 22 states with the hospitalization rate nationwide being at its highest rate this early since the 2009 swine flu pandemic.

Their concerns are heightened by the fact that flu season usually doesn’t ramp up until December or January.

Experts say the early surge was predicated as flu cases were low during the two years of the COVID-19 pandemic and people may not have their usual immunity.

They do note that COVID-19 cases remain at relatively low levels so far this fall.

In addition, an early wave of respiratory syncytial virus (RSV) that has filled many hospitals with children who’ve contracted the illness prompted the Centers for Disease Control and Prevention to issue a warning earlier this month.

Health experts are now getting out the word that a “tridemic” of flu, RSV, and COVID-19 may hit the country this winter as people spend more time indoors and safety protocols are relaxed.

Healthline spoke to two infectious disease experts about the upcoming season, what places have the highest risk of illness, and what you can do to reduce your chances of becoming sick.

Dr. Monica Gandhi, MPH, is a professor of medicine at the University of California San Francisco.

Dr. William Schaffner is a professor of preventive medicine at Vanderbilt University in Tennessee.

Schaffner: Indoor settings with a group of people are the locations where all three of these respiratory viruses can spread easily. This includes business meetings, religious services, parties, concerts, gyms – any and all locations where people are close together in enclosed rooms, particularly if there is vigorous speech, singing, or exertion because that involves deep breathing which can spread the viruses widely.

Gandhi: Unventilated crowded indoor spaces are the most risky in terms of contracting respiratory pathogens, including bars and crowded performances.

Gandhi: You can look at your local Department of Public Health website, which should list the burden and test positivity rates of different viruses, including influenza, RSV, and SARS-CoV-2. The CDC “FluView” website gives data on national surveillance of specimens submitted for respiratory viral testing, although granular data at the level of municipalities is not available.

Schaffner: Local news reports on TV, radio, and in your hometown newspaper are sure to report outbreaks of influenza, RSV, or COVID. Outbreaks can lead to school closures as well as many patients seeking care in emergency rooms, clinics, and hospitals.

Schaffner: First, all of us should be vaccinated with the new updated COVID booster as well as with the annual influenza vaccine. That is fundamental to making all our upcoming holiday festivities as safe as possible.

The second thing is to look at ourselves. If we are in a group that is at higher risk of complications, we need to be particularly careful. Such groups include older adults, anyone who has an underlying illness (for example, heart or lung disease; diabetes), and all who are moderately or severely immunocompromised. Such persons ought to take extra precautions when their community is affected by COVID, flu, or RSV. They are advised to wear masks and to do social distancing, avoiding indoor congregate settings.

Gandhi: Ventilation is probably the most effective non-pharmaceutical intervention to reduce the spread of respiratory pathogens, so look for open windows or HEPA filters. Stay home when sick and move away from others who are actively coughing or sneezing. You can wear a well-fit and filtered mask (N95, KN95, KF94, and FFP2 masks are best) although those can be difficult to wear in venues involving food and drink.