It’s sweater-unpacking season in Boston, and that means it’s flu prep season too.

Flu numbers are low so far, per usual for September. The Boston Public Health Commission confirmed just nine reported cases of influenza since Aug. 1.

But the number of Bostonians catching the virus can only go up from here, beginning in September and slowly picking up speed until the usual peak around late January or February, health officials told Metro.

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“At least right now we don’t have any indicators that it’s going to be an early season,” said Dr. Susan Lett, director of the Boston Department of Public Health’s immunization program.

Your best defense, as always: the flu shot. Think you don’t need one? Think again, said Dr. Anita Barry, director of the city health commission’s infectious disease bureau.

“I would strongly encourage them to consider protection of those around them who might be at higher risk” like seniors, pregnant moms or infants, Barry told Metro. “Plus the flu itself is a miserable illness. It’s pretty nasty.”

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There has been good news from the Southern Hemisphere, where the flu season happens during our off-season, Lett said. Vaccines being used appear to be tackling the latest strains of the virus, she said - an indicator that the flu shot would be more effective than last year, when shots were not adequately tailored to the ever-changing virus.

"The viruses appear right now to be a good match to what is in our vaccine this season," Lett said. "Last year, we didn’t have the vaccine match, but we kind of knew that at this particular point in time because we really always look at the Southern Hemisphere to get a hint at what will happen here."

Experts recommend getting vaccinated by October (though they say it’s never too late), and there are plenty of places to get it done: local pharmacies, college campuses and primary care offices, to name a few. The CDC now recommends shots for everyone 6 months or older.

A well-vaccinated city is good for everyone, said Dr. David Hooper, chief of the infection control unit at Massachusetts General Hospital.

“We have to deal with this every year and, again, the more we can get vaccinated the better off we’ll all be,” Hooper said, adding that his hospital aims to vaccinate every health care worker, excepting those who can’t get the flu shot for medical reasons.