The influenza vaccine is recommended annually for nearly everyone aged 6 months and older, according to the Centers for Disease Control and Prevention (CDC) guidance for the 2025-2026 season, and September through October remains the window most health authorities describe as the best time to be vaccinated for most people. The stakes are not small: CDC estimated that vaccination during the 2023-2024 season prevented roughly 9.8 million influenza illnesses in the United States.
This article explains what the flu shot covers, when timing matters, what the evidence says about effectiveness, and which side effects are expected. Newspaper Daily publishes information, not medical advice; anyone with questions about their own vaccination plan should raise them with a clinician or pharmacist.
Who should get a flu shot this season?
CDC's recommendation for the 2025-2026 season applies to everyone aged 6 months and older who does not have a contraindication to the vaccine. Annual vaccination matters because two things change every year: the circulating influenza viruses evolve, and the protection generated by the previous season's shot fades over months. The vaccine is reformulated each year to match the strains that surveillance laboratories identified as most likely to circulate.
Some groups are treated as priorities in CDC's messaging because influenza hits them harder or because they transmit the virus to vulnerable people. That list includes adults aged 65 and older, pregnant people, young children, residents of long-term care facilities, people with chronic conditions such as asthma, diabetes, or heart disease, and household contacts of infants too young to be vaccinated.
For older adults, CDC's advisory committee has specifically listed preferential options for people 65 and older since 2022: higher-dose inactivated vaccines, an adjuvanted inactivated vaccine, and a recombinant vaccine. Studies cited by CDC found these formulations generate a stronger antibody response in older immune systems than standard-dose shots. A pharmacist can confirm which formulations are in stock locally.
When is the right time to get vaccinated?
CDC's guidance for the 2025-2026 season describes September and October as the ideal vaccination months for most people. The logic is mathematical: antibody protection peaks a couple of weeks after the shot and wanes across the season, so vaccinating too early, in July or August, can leave less protection by the time influenza activity typically peaks between December and February.
There are exceptions to the September-October window. Pregnant people in their third trimester have been advised by CDC to consider vaccination in July or August, so that antibodies pass to the newborn during the first months of life, when infants cannot yet be vaccinated themselves. Children receiving a flu vaccine for the first time need two doses at least four weeks apart, which pushes their timeline earlier. And vaccination is generally considered reasonable any time influenza viruses are still circulating, even deep into the season, because a late shot can still cover later waves.
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How well does the flu shot work?
Effectiveness varies from season to season because it depends on how closely the vaccine's strains match the viruses that actually circulate. CDC's own estimates from recent seasons illustrate the range: vaccination prevented an estimated 9.8 million illnesses, about 4.8 million medical visits, and roughly 259 hospitalizations per 100,000 vaccinated people during the 2023-2024 season, according to CDC's burden estimates published in 2024.
Even in seasons with a partial mismatch, the vaccine's most important benefit holds up: reduced severity. CDC consistently reports that vaccination lowers the risk of hospitalization and death among people who catch influenza anyway. Interim estimates from recent seasons, cited in CDC's Morbidity and Mortality Weekly Report, found vaccinated adults who were hospitalized with flu had markedly lower odds of severe outcomes than unvaccinated patients.
What about side effects?
The most common side effects, per CDC's vaccine information statements, are soreness, redness, or swelling at the injection site, plus low-grade fever, muscle aches, and headache in some recipients. These usually resolve within a day or two. The flu shot cannot cause influenza, because injectable vaccines contain inactivated virus or single proteins, not live replicating virus. A rare but real risk, Guillain-Barré syndrome, occurs at roughly one to two additional cases per million doses in the CDC-cited literature, a rate far lower than the complication risk from influenza infection itself.
Can the flu shot be combined with other vaccines?
Yes. CDC states that influenza vaccines can be administered on the same visit as COVID-19 vaccines and other routine immunizations. Pharmacies have made this a one-stop visit in most states. Consumers taking an anticoagulant or living with a bleeding disorder are typically advised by clinicians to mention it before the injection, though it is rarely a barrier.
Who should not get a flu shot?
Contraindications are narrow. CDC lists a history of severe allergic reaction to a previous dose of any influenza vaccine or to a vaccine component as a contraindication. People with an egg allergy can receive any flu vaccine recommended for their age under 2023 CDC guidance, which removed special precautions for egg-allergic recipients, because the egg protein content in current formulations is too low to matter clinically.
When to see a doctor
Anyone who develops difficulty breathing, hives, swelling of the face or throat, dizziness, or a rapid heartbeat shortly after vaccination should seek medical care immediately, since those signs can indicate a severe allergic reaction. Outside the vaccination context, influenza itself warrants a clinician's attention when symptoms include shortness of breath, chest pain, persistent high fever, confusion, dehydration, or improvement followed by sudden worsening. CDC notes that antiviral treatment works best when started within 48 hours of symptom onset, particularly for people in higher-risk groups.