The best time to get your flu shot is early fall

• The best time to get a flu shot is in the early fall, particularly in late Sept. or early Oct.
• This gives you time to build up protective antibodies to the virus before the height of flu season.
• The flu shot lasts for 6 months, so if you get it in Oct. it will protect you through flu season end.

Flu shots are the most effective way to help prevent getting the flu and the dangerous complications associated with a serious case of influenza. In the 2018-2019 flu season, experts estimate that the vaccine prevented about 4.4 million illnesses.

The flu vaccine is usually offered from late September all the way until January or February of the following year. But just because flu clinics are open through February doesn't mean you should wait that long to get vaccinated.

The best time to get a flu shot

If you live in the Northern Hemisphere, the best time to get your flu shot is in the early fall, particularly in late September or October. In fact, the Center for Disease Control and Prevention (CDC) recommends that everyone get a flu vaccine by the end of October so they are protected for the entire flu season.

The flu vaccine protects you for six months, so if you get it in mid-October it should protect you through mid-April, which is through all of the flu season, which typically ends in March.

Moreover, it's important to get vaccinated early when the flu isn't running rampant yet because the shot takes about two weeks for your body to produce enough antibodies to protect against infection, says Robin Lopez, PA, a Physician's Assistant at Community Health of South Florida, Inc.

That means you can still get sick with the flu within those two weeks while you're building up immunity. So, it's less likely you'll get the flu if you're vaccinated early when the flu virus infection rates are still low.

Note: A 2018 study that tracked 44,959 patients for seven flu seasons, found what's called a waning effect. Every 28 days after receiving the shot, the participants in the study demonstrated that their risk of getting the flu increased by 16%. So, there is a chance that early vaccination may mean you're less protected come flu season's peak from December through February.

Is it too late to get a flu shot?

As long as the flu shot is being offered, it is never too late to get vaccinated, says Lopez.

But the end of February is the latest that vaccines are available in the Northern Hemisphere. Once March begins, the CDC and other scientists start collating data for the production of the following year's vaccines.

The only risks associated with getting the flu shot late is that you might get the flu. And if you haven't had the vaccine the illness could prove more serious, especially if you're in a high-risk group.

So you can and should get immunized whenever you can, even if you've already become sick with the flu.

Insider's takeaway

Getting a flu shot at any point during flu season is better than no flu shot at all. However, timing is a factor in determining how well you're protected.

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While the vaccine does have a waning effect, dropping 16% in efficacy every 28 days, the antibodies your immune system builds up against the influenza virus are generally effective for six months.

The CDC and healthcare providers recommend that every eligible person from the age of six months up to be vaccinated by the end of October.

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