In the United States, annual flu vaccine campaigns begin in early September, before temperatures start to cool down and the cycle of people catching and spreading virus commences.

The Centers for Disease Control and Prevention recommends that most people get vaccinated as soon as updated shots become available for the season. And in an ideal world everyone would be vaccinated by the end of October.

But what if you missed the pop-up vaccine clinic at work and put off going to a pharmacy or doctor’s office for your shots?

Experts, including those at the CDC, say it’s better to get the vaccine late than to skip it. Flu season runs from October to May, with a peak usually occurring in February. Getting vaccinated at any time during the season can keep you from falling ill and missing work or school.

Vaccine effectiveness can vary a lot depending on the season. But even when the vaccine fails at preventing infection, it can still reduce the severity of symptoms and lower your chances of hospitalization, said Dr. Sean Liu, an assistant professor of infectious disease at the Icahn School of Medicine at Mount Sinai in New York City. In vulnerable groups, like pregnant women, older adults and very young children, the vaccine can also save lives, Liu said. A 2022 study in children, for example, found that the flu vaccine reduced children’s risk of severe life-threatening influenza by 75%.

When more people get vaccinated, it reduces everyone’s risk of exposure. “By getting vaccinated against the flu you are not only helping protect yourself, you are indirectly helping to protect those people in the community who are at higher risk of getting sick,” Liu said.

Scientific evidence from decades of flu vaccine monitoring in the United States shows that the vaccines have an excellent safety profile and minimal side effects. Most of these side effects, such as muscle aches, headaches and a general feeling of malaise, are signs that your body is learning how to fight influenza based on pieces of the virus in the vaccine.

For those who fear needles or want to avoid injection site soreness, there’s an option to get FluMist, a vaccine that is sprayed into the nose and is appropriate for those 2 through 49 years old. But the spray is available at fewer pharmacies compared with the availability of shots.

It takes about two weeks after vaccination for your immune system to make enough antibodies to protect against the flu. “It’s not like a light switch,” said Dr. William Schaffner, a professor of preventive medicine at the Vanderbilt University School of Medicine.

Additionally, children 6 months through 8 years who are getting vaccinated for the first time need two doses, spaced about a month apart, to get the full antibody protection. Ideally you would plan to get your vaccines with enough time before flu activity increases and in advance of any big travel plans or family gatherings, Schaffner said.

While you should probably wait a few weeks to get vaccinated if you are actively sniffling and feverish, there is still a benefit to getting vaccinated after you’ve recovered from the flu.

“Having flu more than once in a season is not unheard-of,” Schaffner said. That’s because there are often several strains of influenza virus circulating every season, and infection with one doesn’t necessarily protect you from another.

Flu vaccines, however, are designed to protect against four different strains of influenza that scientists expect to be dominant each season. (You may see the word “quadrivalent” on immunization posters and in vaccine brand names.)

And unless you have a positive test confirming that you had the flu, it’s also possible to confuse it with symptoms of the common cold, RSV, COVID or several other respiratory viruses circulating around the same time, Schaffner said.

Most pharmacies, primary care doctors, urgent care centers and county health departments carry flu vaccines well into spring. You can use the CDC’s vaccines.gov database to find a location near you.

This article originally appeared in The New York Times.

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