Over 11,200 patients in the US were hospitalized with flu, the highest since 2010, according to data released by the Centers for Disease Control and Prevention (CDC).
Seasonal influenza activity is elevated across the country, Xinhua news agency quoted the CDC as saying on Monday.
Five flu-associated paediatric deaths were reported in the week ending November 19, which increased the overall number to 12, according to the CDC.
The CDC estimates that so far this season there have been at least 6.2 million flu illnesses, 53,000 hospitalisations and 2,900 deaths from flu.
Of influenza A viruses detected and subtyped this season, 78 per cent have been influenza A (H3N2) and 22 per cent have been influenza A (H1N1), according to the CDC.
Thanksgiving holiday gatherings have amped up the spread of viruses such as flu, coronavirus and respiratory syncytial virus (RSV).
RSV and flu are both at high levels for this time of year.
"We have seen, in some regions, RSV numbers starting to trend downward. Flu numbers are still on the rise. And we are concerned that after holiday gathering, lots of people coming together, that we may see increases in Covid-19 cases as well," said CDC Director Rochelle Walensky.
Top infectious diseases expert Anthony S. Fauci warned RSV could become public health emergency in the US.
"It is if in fact, which in some regions of the country, we're seeing that the hospital system for paediatrics are at the point of almost being overwhelmed," Fauci told CBS News on Sunday.
The CDC said an annual flu vaccine is the best way to protect against flu. Vaccination helps prevent infection and can also prevent serious outcomes.
The CDC recommends that everyone ages 6 months and older get a flu vaccine annually.
For a half-century, scientists have been trying to develop a vaccine that would protect against the most dangerous flu viruses.