You Can Get the Flu Twice in One Season

There's a lot of time during flu season to dodge germs. Influenza activity peaks from December to February, but it can easily stretch from November (or earlier) to March (or later).

So if you had the flu already this year—or got the flu shot—you might feel like at least you got your turn out of the way. Except it doesn't exactly work that way. During these long flu season months, you could get the flu a second time. Yes, really.

What Are the Types of Influenza?

There are four different types of flu: influenza A, B, C, and D. Influenza A and influenza B cause the seasonal epidemics we've come to expect in the fall and winter, and there are different strains of each. When you get sick from one particular strain of flu virus, your body develops an immune response that will protect you from getting re-infected with the very same bug.

"Your likelihood of getting the same flu again is lower," Denise Pate, MD, internal medicine physician with Medical Offices of Manhattan, told Health. "However, you can become infected with a different strain, and the antibodies you formed from the first bout are not providing protection."

Who Chooses Which Flu Vaccine Gets Used?

The World Health Organization (WHO) vaccine committee recommends the specific flu virus for the upcoming flu season. Then, that vaccine is manufactured and distributed to healthcare providers and ready to go into your arm and offer protection.

Sometimes the recommended vaccine does not work as effectively as hoped. For example, the 2018 flu shot was not that effective against that year's dominant strain of influenza A, H3N2—it was effective 36 percent of the time. If you got the flu from this particular virus in, say, December, you could encounter another form of the bug—like H1N1 or influenza B—in February and get sick again.

“It is not uncommon for there to be second waves of influenza B virus activity later in the flu season,” Sonja Olsen, PhD, in the influenza division of the Centers for Disease Control and Prevention (CDC), told Health. “[In 2018], both the proportion of H1N1 and influenza B viruses in circulation is increasing.”

At least getting the flu once doesn't give you a higher risk of going in for a second round.

Who Should Get the Flu Shot?

Most people over the age of six months are recommended to get the flu shot. Some shots are only for adults, so discuss with your healthcare provider which one you should get. Also, some people should only get certain types of flu shots. Talk with your healthcare provider about if and which vaccine to get if one of the following describes you:

• You have an allergy to egg proteins or other ingredients in the flu shot
• You had Guillain-Barre Syndrome, a paralyzing illness, at some point
• You had a bad reaction to a previous flu shot
• You are pregnant
  

When Should You Get the Flu Shot for the Best Protection?

It’s not too late to get your flu shot. This applies even if you already had the flu once this season. "Despite getting the flu, you are still eligible and should get the flu vaccine," said Dr. Pate. "This will provide added protection against the strain of the flu you had, in addition to protecting you from the other strains of influenza that are circulating."

September and October are the ideal months to get your flu shot. You can get your shot after October, and it'll still be effective through the peak flu months. Getting the shot in July and August won't have much effect during the flu season.

A Quick Review

Even if you already had influenza this flu season, which peaks from December to February, it is possible to get it again. Your chances of being infected again by the same strain may be low, but there are two types of flu-causing viruses, and each has different strains that lead to the illness—plenty of opportunity to make you sick.

The best months to get the shot are September and October because the shot should cover the whole peak season. Talk with your healthcare provider to find out which type of flu shot is right for you.