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The Centers for Disease Control and Prevention is urging people not to let the poor performance of last year’s vaccine keep them from getting a flu shot this year.

Overall, the 2017-2018 flu vaccine was 40 percent effective, the CDC says. However, it was only 25 percent effective against the nasty H3N2 strain of flu.

Drugmakers have been working since February to reformulate the 2018-2019 vaccine. It has been updated to better fight H3N2, an influenza A strain, and it targets different strains of influenza B than last year’s shot.

Dr. Richard Webby, an infectious disease expert at St Jude Children's Research Hospital, told Business Insider, "What we hope is that it's going to be a better match to what's circulating.”

Webby said the mild flu season Australia has been experiencing could indicate the new vaccine is a better match this year.

(MORE: CDC Says 80,000 People Died of the Flu Last Winter in the U.S.)

The CDC says the vaccine remains the best way to prevent the flu and the serious complications it can cause. It estimates that last year’s vaccine still prevented 5.3 million illnesses, 2.6 million influenza-associated medical visits, and 85,000 hospitalizations associated with flu.

Everyone 6 months old and older should have an annual flu shot, the CDC says. Several options are available, including a stronger version for older people and a nasal mist version.

Flu activity often begins as early as October and November and can continue to occur as late as May, according to the CDC. Flu activity most commonly peaks in the United States between December and February. 

It takes about two weeks after you get the shot for your body’s immune response to fully respond and for you to be protected. The CDC recommends getting the vaccine by the end of October, but getting the shot later can still be beneficial.

Even if you do catch the flu after getting the vaccine, the CDC says it could make your illness milder.

The CDC has made an online Vaccine Finder available to help people find places to get the vaccine.