Getting vaccinated late during flu season is still worth it, even if you missed the optimal time in the fall. (Image credit: PeopleImages.com – Yuri A via Shutterstock)
Each year, as fall brings shorter, cooler days to the Northern Hemisphere, we are reminded once again of the importance of getting a flu shot. In the United States, the Centers for Disease Control and Prevention (CDC) recommends that all children over six months of age get a flu shot annually.
Is there a time limit to getting the flu shot? While it’s best to get vaccinated before the season starts, it’s still a good idea to get it closer to the end of the season, two infectious disease experts told Live Science. That advice is especially relevant in light of the 2024-2025 flu season, which is projected to be particularly “severe,” according to the CDC. That’s because the flu strains circulating this season are more likely to cause complications and affect young children more often than usual.
Flu vaccines typically become available in late summer. Some groups, such as women in late pregnancy, may want to consider getting vaccinated in the summer. However, the CDC recommends that most people eligible for the vaccine get it in the fall, by late October, because that's when illnesses tend to spike.
“In the U.S., we often recommend getting vaccinated in October because that's when cases start to rise, and we know that the flu vaccine provides good protection for a period of time,” Dr. Sabrina Assoumou, an assistant professor of medicine at Boston University and a physician at Boston Medical Center, told Live Science.
If for any reason you missed this deadline, you should still get a flu shot.
“Flu season typically runs through March, and it usually takes about two weeks after vaccination for the immune system to begin to respond,” Dr. Daniel Kuritzkes, chief of infectious diseases at Brigham and Women’s Hospital in Boston, told Live Science in an email. So even if you haven’t gotten a shot yet, it’s worth getting one before the end of February, and perhaps even before early March, he added.
Additionally, there is “no harm” in getting vaccinated after March or April, given that flu viruses can circulate year-round, Kuritzkes said. However, as a practical matter, the risk of getting the flu in the spring or summer is “so low” that health officials typically don’t focus on vaccination after the season ends, he added.
If you haven’t gotten sick by January, it can be tempting to think, “Oh, the holidays are over; I’ve avoided the flu,” Assoumou said. However, the peak of cases can start as early as February and continue throughout the flu season. The later you get vaccinated, the shorter your window of available protection will be during that particular season, Assoumou added.
Notably, in recent years, COVID-19 has made it difficult to predict the peak of flu season.
Influenza transmission in the United States typically peaks in February, but the COVID-19 pandemic has temporarily changed this timing. For example, in 2020, influenza transmission reached historically low levels. Cases began to increase again between 2021 and 2022, peaking in late December 2021 and again in April 2022, but transmission remained high until mid-June. Then, in 2022 and 2023, transmission peaked in late November and early December. In 2024 and 2025, influenza transmission appears to have returned to its normal pattern, with high transmission occurring from late December through February.
This suggests that “we are returning to more familiar patterns of influenza epidemiology,” Kuritzkes said, which is why flu vaccination in the fall remains most important, he added.
Sourse: www.livescience.com
