New Canaan residents will be able to get flu shots on Sunday, Oct. 14, from 1 to 3:30 p.m. in the New Canaan High School gym. The Health Department will vaccinate those 9 and older. The cost is $30 and can be paid by check, credit or debit card, cash or Medicare.

Public health nurse Bethany Zaro said that New Canaan has an ample supply of the vaccine this year and that everyone should get the shot if they can.

"It is very important," she said. "No. 1 it's very safe. CDC now recommends children 6 months and older to get a shot, that's how safe it is. Even if you think you are healthy, you don't need the vaccine, but if you get it you are helping others who are not fortunate enough to be so healthy."

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Manufacturers are slated to make 146 million to 149 million flu vaccine doses this season, according to CDC estimates. Tom Skinner, a CDC spokesman, said that is expected to more than cover those who want the shot nationwide.

Zaro explained why the flu changes and why a new shot is necessary each year.

"The strains are different every year because they mutate. Just because you get it this year doesn't mean you will be protected next year. The world of microbes is really smarter than we are. They change their DNA and structures to try to fool our bodies so we can't fight off the strains."

Skinner said there's no way of telling what the flu season will bring each year.

"We can't really predict what kind of flu season we are going to have because each one is unique in itself," Skinner said. "We do know we are going to have an active flu season and vaccination is the best way to remain healthy and avoid infection."

What viral strains are chosen to be protected against in a given year's three-virus vaccine is made by the CDC in conjunction with the World Health Organization, the Food and Drug Administration and other institutions based on studying viruses circling the globe six to eight months before flu season begins, Skinner said. The three circulating viruses believed most likely to cause illness because of their contagiousness or prevalence during the season are included in the vaccine, Skinner said.

"We make the selection in February and try to guess based on what is going on around the world," Skinner said.

The federal Centers for Disease Control guidelines recommend everyone over the age of 6 months get the flu shot, especially those older than 65.

Flu season usually begins in mid- to late November, is most active from December through February and runs into April or sometimes into May.

Staff writer Tyler Woods contributed to this article. twoods@bcnnew.com; 203-972-4413; https://twitter.com/Woods_NCNews