Last year was the deadliest flu season in the U.S. in four decades.

Health officials are on high alert as this year’s season begins.

"The biggest conversation I am having here around the hospital with a lot of the staff — influenza last year was really profound, even compared to prior years,” said Dr. Kevin Shiley, director of infection prevention and control for Catholic Health. “A lot of significant illness in the hospital and I have been reminding a lot of the staff it's so important to get the influenza vaccine early this year so we are prepared for patients."

This year, it’s the H3N2 strain circulating and making people sick.

It's known to be aggressive and as deadly.

The vaccine is expected to be a better match to the illness, Dr. Shiley said, but it’s still too soon to know how the season will rate.

"From my perspective locally, the biggest thing we can do is remind people that influenza is a really significant illness," he said.

The best time to get vaccinated is before the end of October as it takes about two weeks for it to do its job.

Flu season typically starts in November and peaks in February.

Besides infants, those with chronic illness and those 65 or older are most vulnerable.

But last year, even healthy adults fell gravely ill.