The U.S. is facing a more severe flu season this year, coinciding with an increase in COVID-19 transmission and a surge in cases of respiratory syncytial virus (RSV).

The flu has arrived significantly earlier this year, causing more hospitalizations at this point in the season than in the past decade, according to the latest data from the U.S. Centers for Disease Control and Prevention (CDC).

The southeast and south-central areas of the country reported the highest levels of flu, according to the CDC.

The CDC estimates that, so far this season, there have been at least 880,000 flu illnesses, 6,900 hospitalizations, and 360 deaths from flu nationwide.

The first flu-related pediatric death of the season was reported in the week ending October 22, according to the CDC.

The CDC recommends that everyone aged 6 months and older get a flu vaccine annually.

"Vaccination helps prevent infection and can also prevent serious outcomes in people who get vaccinated but still get sick with flu," said the agency.

"It's unusual, but we're coming out of an unusual COVID pandemic that has really affected influenza and other respiratory viruses that are circulating," Lynnette Brammer, epidemiologist and head of the CDC's domestic influenza surveillance team, told The Washington Post.

Brammer added that this season's flu vaccine is well matched against the circulating viruses, urging vaccinations as soon a possible.

Health experts warned a "tripledemic" of respiratory illness this winter caused by an earlier-than-normal flu season, a surge in RSV cases and increase in COVID-19 transmission.

In particular, RSV infections among young children are filling some U.S. hospitals to capacity.

Surveillance data collected by the CDC clearly shows a rise in RSV cases nationwide in recent weeks, with cases detected by PCR tests more than tripling over the past two months.

Children with underlying health conditions, such as chronic lung disease or heart problems, may also be at higher risk for severe illness from respiratory viruses, said Dr. Nusheen Ameenuddin, a pediatrician at the Mayo Clinic in Rochester, Minnesota.

Moreover, the COVID-19 cases caused by new variants are growing fast in the U.S., CDC data shows.

Two new variants, BQ.1 and BQ.1.1, have been growing especially fast. At the beginning of October, each one accounted for about 1 percent of new infections in the U.S., but they have been roughly doubling in prevalence each week.

According to the latest CDC data, the two variants accounted for more than one in four new COVID-19 infections nationwide.

"We're in a very challenging phase," said Syra Madad, an epidemiologist who helps oversee pandemic response for NYC Health and Hospitals, the nation's largest municipal health-care system.

"Barely anybody is masking. We have very low vaccination rates for the updated boosters, as well as generally waning immunity. And to top it all off, we have these highly immune-evasive subvariants that are circulating," Madad told The Washington Post.

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Health experts concerned over triple threat of flu, COVID, RSV in U.S.