It’s a question I’ve heard behind the pharmacy counter for years: “I got a flu shot last year. Do I really need another one?”
The short answer is yes—for most people, an annual flu vaccine is still recommended. But the reason why is more interesting than simply saying, “because you need one every year.”
Flu viruses change. Protection from vaccination can decrease over time. And each year’s vaccine is selected with the upcoming flu season in mind.
So let’s talk about what that actually means—and what I tell patients when they ask me this question.
Why do I need another flu shot?
There are two main reasons: the flu virus changes, and protection from vaccination can decrease over time.[1–4]
Influenza viruses are constantly evolving. This is called antigenic drift—small genetic changes that can alter the viruses circulating from one flu season to the next.[1] Because of this, scientists review circulating influenza viruses and update the vaccine composition to better match what they expect to circulate during the upcoming season.
This year is a particularly good example. For the 2026–27 flu season, all three virus components in U.S. seasonal flu vaccines were updated compared with the previous season.[2]
The second reason is that vaccine protection can wane over time. Studies have found that influenza vaccine effectiveness can decrease as the months pass after vaccination, although the amount of waning varies by influenza strain, age, and other factors.[3,4]
So I don’t think of the flu shot as a vaccine you get once and are “done” with. It’s better thought of as protection that is updated and refreshed for each flu season.
But how well does the flu shot actually work?
This is where the answer gets a little more complicated.
Flu vaccine effectiveness isn’t the same every year. It depends on several things, including which influenza viruses are circulating, how closely the vaccine matches those viruses, and characteristics of the person being vaccinated.[5]
Getting vaccinated also doesn’t mean you absolutely cannot get the flu. What we’re trying to do is reduce the likelihood of getting sick and, importantly, reduce the risk of serious illness and hospitalization.
The 2025–26 season is a useful real-world example. Interim U.S. data found that among adults, flu vaccination reduced the risk of influenza-related outpatient visits by about 22% to 34% and influenza-related hospitalization by about 30%. Among children and adolescents, protection against influenza-related hospitalization was approximately 41%.[5]
Those numbers may not sound spectacular—and I think it’s important to be transparent about that. Flu vaccines are not perfect. But when influenza is circulating widely, even partial protection can make a meaningful difference, particularly for people at greater risk of complications.
If I can still get the flu after the vaccine, what’s the point?
Preventing every single infection isn’t the only measure of whether a vaccine is useful.
Vaccination can reduce the risk of influenza-related hospitalization, and research has also found that among some people hospitalized with influenza, prior vaccination was associated with less severe illness.[5,6]
This matters even more for people who are at higher risk of developing serious flu complications, including older adults, young children, pregnant women, and people with certain chronic medical conditions.[7]
So when a patient tells me, “I got the flu shot and still got the flu,” I don’t dismiss that experience. It can happen.
The better question is: Did vaccination reduce the chance of getting seriously ill?
That’s an important part of what we’re trying to accomplish.
“I got a flu shot once—and then I got sick.”
I hear this one a lot: “The last time I got a flu shot, I got sick right afterward, so I stopped getting them.”
There are a few possible explanations.
The flu shot cannot cause influenza. The vaccines given by injection use either inactivated influenza virus or influenza proteins rather than infectious virus capable of causing flu.[7] They can, however, cause temporary side effects such as soreness, fatigue, headache, muscle aches, or fever—and those symptoms can certainly make you feel under the weather for a day or two.
It’s also possible to become infected with influenza shortly before vaccination or during the roughly two weeks it takes the body to develop protection after vaccination.[7] And plenty of other respiratory viruses circulate during flu season, so getting “sick” after a flu shot doesn’t necessarily mean you had influenza.
Finally, as we discussed above, flu vaccination isn’t 100% effective. Some vaccinated people will still get influenza.
So if someone tells me they got sick after their flu shot, I don’t tell them they imagined it. The timing may have been very real—but that doesn’t necessarily mean the vaccine caused the illness.
When should I get my flu shot?
For most people who need one dose for the season, September or October is generally a good time to get vaccinated against influenza.[8]
There’s a reason I don’t necessarily tell every patient to get their flu shot the moment the first shipment arrives in the summer. Protection can decrease over time, and flu season can stretch well into the winter and spring. Most adults—particularly adults 65 and older—generally should not get vaccinated early in July or August unless there is a reason to do so.[8]
There are exceptions. Some children need two doses of flu vaccine given at least four weeks apart and may need to start earlier. Vaccination during July or August can also be considered during the third trimester of pregnancy and for people who might not have another opportunity to be vaccinated later.[8]
And if September or October has already passed? It’s usually not too late. Vaccination should generally continue while influenza viruses are circulating and vaccine is available.[8]
In practical terms, I tell most patients: don’t worry about finding the perfect day. Aim for September or October, and if you miss that window, getting vaccinated later can still be worthwhile.
Who should get a flu shot?
The simple answer is: almost everyone 6 months of age and older should receive a flu vaccine every year, unless there is a specific reason they shouldn’t.[8]
Vaccination is particularly important for people at higher risk of serious complications from influenza—including adults 65 and older, young children, pregnant women, and people with certain chronic medical conditions.[7,8]
The specific vaccine can matter, though. Age, pregnancy, medical conditions, previous vaccine reactions, and other factors can affect which flu vaccine is appropriate. For example, for adults 65 and older, certain flu vaccines are preferentially recommended.[8]
One question I still hear surprisingly often is, “I’m allergic to eggs—can I get a flu shot?”
Yes. Current guidance says that people with egg allergy can receive any influenza vaccine that is otherwise appropriate for their age and health status. Egg allergy alone does not require additional safety precautions beyond those recommended for any vaccine recipient.[8]
If you’ve had a serious reaction to a previous flu vaccine, have a history that makes you unsure about vaccination, or simply don’t know which vaccine is right for you, that’s a good reason to talk with your pharmacist or healthcare provider rather than automatically skipping it.
The bottom line from behind the pharmacy counter
After more than 20 years behind the pharmacy counter, I’ve learned that most vaccine questions aren’t really about memorizing statistics. People want to know whether something is necessary, whether it works, what the risks are, and whether the benefits make sense for them.
The flu vaccine isn’t perfect. It doesn’t guarantee you won’t get influenza, and its effectiveness varies from season to season.
But influenza viruses change, protection from vaccination can decrease over time, and the vaccine is updated as circulating viruses change. That’s why, for most people, getting vaccinated every flu season still makes sense.
And if you have questions before getting vaccinated—ask them.
A good vaccine conversation shouldn’t be about pressuring someone into a decision. It should be about giving them reliable information, answering their questions, and helping them make an informed choice.
References
1. Rasmussen SA, Jernigan DB. Antigenic Drift and Antivaccine Shift in the 2025–2026 Influenza Season. N Engl J Med. 2026;394:732–735. doi:10.1056/NEJMp2600395. New England Journal of Medicine
2. Centers for Disease Control and Prevention. 2026–2027 Flu Season. Updated September 29, 2026. Accessed October 4, 2026. CDC
3. Young B, Sadarangani S, Jiang L, Wilder-Smith A, Chen MIC. Duration of Influenza Vaccine Effectiveness: A Systematic Review, Meta-analysis, and Meta-regression of Test-Negative Design Case-Control Studies. J Infect Dis. 2018;217(5):731–741. doi:10.1093/infdis/jix632. PubMed
4. Doyon-Plourde P, Przepiorkowski J, Young K, Zhao L, Sinilaite A. Intraseasonal waning immunity of seasonal influenza vaccine—a systematic review and meta-analysis. Vaccine. 2023;41(31):4462–4471. doi:10.1016/j.vaccine.2023.06.038. PubMed
5. Centers for Disease Control and Prevention. Interim Estimates of 2025–26 Seasonal Influenza Vaccine Effectiveness—United States, September 2025–February 2026. MMWR Morb Mortal Wkly Rep. 2026;75(9):116–123. CDC
6. Arriola C, Garg S, Anderson EJ, et al. Influenza Vaccination Modifies Disease Severity Among Community-dwelling Adults Hospitalized With Influenza. Clin Infect Dis. 2017;65(8):1289–1297. doi:10.1093/cid/cix468. PubMed
7. Centers for Disease Control and Prevention. Seasonal Flu Vaccine Basics. Updated September 1, 2026. Accessed October 4, 2026. CDC
8. Centers for Disease Control and Prevention. Interim Clinical Considerations for the Use of Seasonal Influenza Vaccines in the United States, 2026–2027. Updated September 1, 2026. Accessed October 4, 2026.
The Vax Desk provides general educational information and is not a substitute for individualized medical advice. Vaccine recommendations can change and may vary based on age, medical history, medications, pregnancy, and other factors. Talk with your pharmacist or healthcare provider about recommendations specific to you.