Flu season is coming! Time to get vaccinated!

Last year's flu season was awful, but health officials say there's a simple way that could help prevent a rerun of that this season.

Officials on Thursday urged—repeatedly—every person in the country over the age of 6 months to get vaccinated for the flu, noting that vaccines are the single best way to prevent getting sick from the bug and losing days of work and school.

"This is the beginning of the flu season, there's plenty of vaccine out there," said Dr. Tom Frieden, director of the U.S. Centers for Disease Control and Prevention. "Get a flu shot to prevent yourself, your family and your community.... Flu is a potentially serious illness."

Frieden said 171 million doses of flu vaccine are being produced for this season, with about 40 million doses already distributed. He said that amount of vaccine would be enough to meet demand.

The current vaccine, which has been modified to target a strain that causes millions of illnesses last year, "should be a good match against this season's influenza, but only time will tell," Frieden said.

Read More Additional information about the flu

The CDC for the past five years has recommended that everyone older than 6 months get vaccinated. Despite that recommendation, less than half of the U.S. population, or an estimated 47 percent, got a flu vaccine last season, and just 34 percent, for the 18-to-49-year-old age group received a vaccination.

"Unfortunately, many people are still unaware of this universal recommendation," said. Dr. Kathleen Neuzil, director of the Center for Vaccine Development at the University of Maryland School of Medicine.

Neuzil said some people avoid getting vaccinated because they believe they are "invincible." But even those people can get the flu, and should get vaccinated to prevent themselves from getting sick, and from spreading the flu to other people particularly vulnerable to the bug, including children, seniors and pregnant women.

A recent study found that people over the age of 65 were less likely to get a flu-related illness when a third of younger adults in their area are vaccinated.

Officials noted that people can get flu shots in a variety of locations, including from their doctors, pharmacies and workplaces.

Frieden said that increasingly, "businesses recognize that vaccinating their employees is very good business," because it reduced worker absenteeism due to the flu.

Frieden, who himself got a flu shot during a media briefing Thursday, noted that even in a "good year" for flu, there are "millions of cases of illness, hundreds of thousands of hospitalizations and thousands or tens of thousands of deaths."

Last season, which spanned the fall of 2014 into the winter of 2015, was anything but "good" for the flu.

"This was a bad year," said Frieden. The season "had the highest hospitalization rate among seniors we have ever documented," he said.

There was also 145 documented deaths of children from the flu, although the actual number of pediatric deaths from influenza was undoubtedly "much higher," Frieden said.

Last season "was unusual" for the flu, said Dr. William Schaffner, medical director of the National Foundation for Infectious Diseases.

"Not only did we have one strain of influenza that caused almost all of the reported flu cases, but it was different, it had mutated ... it had changed and as a consequence quickly become the predominant strain," Schaffner said.

The strain was the "Switzerland variant" of H3N2, which officials noted tends to hit senior citizens particularly hard.

Normally, flu vaccine tends to be "about 50 to 60 percent effective" against influenza, Frieden said. But last year, the vaccine was only about 13 percent effective against what become the predominant strain, he said.

The flu vaccine produced for this year has last season's predominant strain in it, along with other strains that have been prevalent in the Southern Hemisphere of the world recently, he said.

Flu vaccines come in two main types: trivalent and quadrivalent, which have three or four strains of flu in them, respectively.

Frieden said that among 199 recently analyzed flu specimens in the U.S., most of them, or 118, were the H3N2 type that is closely related to the strain in this season's vaccine.

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