Doctors often use the phrase “flu before boo” to remind people to get their flu vaccine before Halloween. But this flu season, you might not want to wait until Oct. 31 to get vaccinated. Centers for Disease Control and Prevention (CDC) that shows an uptick of flu cases in the U.S. in recent weeks.
However, we've been seeing some flu activity in the last few weeks that seems to be sticking around,” says Martin, who studies the spread of respiratory viruses and vaccine effectiveness. Getting the flu shot now is a good idea, Martin says, as it takes about two weeks for the vaccine to become fully effective. She adds that October is generally an ideal time to get the flu vaccine because it not only offers protection from early waves of the virus, but also gives continued coverage through January and February when flu cases are typically at their peak.
So if you have an opportunity to get it, don't overthink the timing.” Martin says she plans on getting the flu shot next week. The flu vaccine is available as a shot or nasal spray. For the first time, a flu shot using mRNA technology is available this year.
In a study published in May 2026, the mRNA-based flu shot, produced by Moderna and called mFlusiva, was up to 27% more effective in preventing flu than any of four currently available flu shots. Food and Drug Administration (FDA) has approved mFlusiva for people ages 50 and older. You need to get a flu vaccine every year to stay protected against the virus as flu strains are constantly evolving, and immune protection against the flu decreases over time. (That is also true if you get sick from the flu, Martin says.
Natural immunity also wears off.) Flu vaccination helps prevent infection and significantly reduces the risk of severe disease and death. The CDC estimates that flu vaccination prevented 10 million flu-related illnesses, 180,000 flu-related hospitalizations, and 12,000 flu-related deaths in the U.S. during the 2024–2025 flu season. But flu vaccination rates have been declining across the U.S. in recent years.
Flu vaccination among children fell from 63% in the 2019–2020 flu season to 50% in 2024–2025—a drop of 13 percentage points. About 300 children died in 2024-2025 because of complications related to the flu. Most of them were unvaccinated, the CDC says.
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