For most people, September or October is the best time to get a flu shot, before the cold weather promotes the spread of respiratory viruses. This is even more important for older adults, who face a bigger risk of serious illness and complications from the flu. Timing your flu shot right can help protect you throughout the fall and winter flu season.

This guide explores when you should get your flu shot, how long protection lasts, and which vaccines are recommended for older adults.

Quick Guide: When Should You Get a Flu Shot?

How serious is the flu?

The 2024–2025 flu season was especially severe. Flu-related hospitalizations and outpatient visits reached their highest levels in 15 years, with more than 710,000 hospitalizations and 45,000 deaths.^1,2 In 2025, flu and pneumonia rose to the eighth leading cause of death in the U.S., up from 11th the previous year.³

While flu seasons vary in severity, older adults consistently face some of the greatest risks. According to the Centers for Disease Control and Prevention (CDC), people age 65 and older account for an estimated 70%–85% of seasonal flu-related deaths and 50%–70% of flu-related hospitalizations.⁴ 

But getting sick with the flu is not inevitable. The flu vaccine is a simple, effective way to boost your defenses against the virus, and timing it just right can maximize its protective benefits. Here’s what you need to know about when to get your flu shot this season.

When does flu season start and end?

Flu season generally starts in October, peaks between December and February, and continues through May. During this period, flu and other respiratory viruses (e.g., COVID and RSV) circulate more actively, increasing your chances of getting sick if you're not protected. But, it’s worth noting that the timing and severity of flu season can vary each year based on factors like the weather (germs travel better in dry air) and how the virus is spreading.

Understanding the basic timeframe for seasonal flu can help you know when to receive your flu shot.

When is the best time to get the flu shot?

According to CDC, the ideal time to get your flu shot is at the start of the season, such as in mid-September or October. The flu vaccine takes about two weeks to become fully effective, so getting it early means you’ll be protected when flu activity spikes in late fall and winter. Since immunity wanes over time, it's not recommended for older adults to get vaccinated earlier than this.

“Getting your flu shot in August may be a little too early if you want your protection to have staying power through the entire flu season,” said Dorothea Vafiadis, NCOA Senior Strategist for Healthy Aging. “Waiting until we’re well into September, or even early October, is your best bet.”

CDC routinely recommends that everyone age 6 months and older get a seasonal flu vaccine each year, with very few exceptions.

And soon, older adults will have another flu vaccine option with the approval of mFLUSIVA, the first mRNA flu vaccine in the U.S. for adults age 50+. mFLUSIVA was found to offer stronger protection against the flu than standard-dose flu vaccines.

For adults age 65+, the FDA approved mFLUSIVA based on early research showing it triggered a stronger and more enduring immune response compared with a high-dose flu vaccine. Researchers are continuing to study how well it works in this age group.

mFLUSIVA is expected to be available for the 2026–2027 flu season, although availability, official health guidance, and insurance coverage are still being finalized.

When is it too late to get a flu shot?

What if you miss the September-October vaccination window? Don’t worry! While earlier is generally better, you can get the flu shot later in the season—even into January or beyond. CDC states that it’s fine to get vaccinated any time during flu season, provided unexpired vaccines are still available and flu viruses are still circulating. While waiting until February or later may mean missing peak flu months, the vaccine can still be effective, especially if a second wave of flu cases arises.

Is the flu shot effective?

The effectiveness of the flu vaccine is typically 40-60%, although efficacy changes from year to year based on how well the vaccine matches the strains spreading in the environment. Flu vaccine effectiveness for the 2025-2026 season was found to range from 22%-34%.⁵

In a large clinical trial, Moderna's newly FDA-approved mRNA flu vaccine was found to be 26.6% more effective than a standard-dose flu shot at preventing influenza.⁶ 

But even if vaccine effectiveness falls below these ranges, it can still offer valuable protection by reducing the severity of symptoms and lowering the risk of serious complications. This is good news for older adults, who are more likely to experience severe illness from the flu.

What is the most effective flu shot for seniors?

For people age 65 and older, CDC recommends one of three flu vaccines found to be more effective than standard flu shots:

• Fluzone High-Dose flu vaccine
• Flublok Recombinant flu vaccine
• Fluad Adjuvanted flu vaccine

If these vaccines are not available at the time of administration (and not expected to be anytime soon), adults age 65 and older should get a standard-dose unadjuvanted inactivated flu vaccine instead. People age 65 years and older should not get a nasal spray flu vaccine.

How long does flu immunity last after an infection?

If you’ve had the flu, your immune system develops some natural protection against the specific flu virus that made you sick. That protection can last for months or longer, but it may weaken over time. And it doesn’t mean you can’t get the flu again during the same season.

That’s why you should still get a flu shot even if you’ve had the flu.

“Keep in mind that several different strains of flu can circulate during the same season,” explained Vafiadis. “Getting sick with one strain may not protect you from another. That’s one reason it’s so important to get your flu shot every year; each formulation is designed protect against the latest strains circulating in communities.”

Can I get the flu shot if I’m sick?

If you’re mildly sick—for example, you have minor symptoms like a runny nose or mild sore throat—it’s generally safe to get the flu shot. However, if you have moderate to severe symptoms (especially with a fever), it’s a good idea to wait until you feel better before getting vaccinated. This is because your immune system may be temporarily weakened from working hard to fight off the illness, and waiting ensures the vaccine has the best chance to be effective.

If you’re unsure, talk to your primary health care provider to determine the best timing for your flu shot.

How often should I get a flu shot?

CDC recommends everyone age six (6) months and older get a flu shot every year, especially older adults and others at higher risk for complications. Since protection from the flu shot wears off over time, an annual flu shot helps you maintain optimal immunity. It’s safe and beneficial to get one every flu season—even if it hasn’t been a full 12 months since your last one.

Plus, seasonal flu vaccines are reformulated every year to protect against the influenza strains scientists think are most likely to circulate. This is where the mRNA-based flu vaccine, mFLUSIVA, has a key advantage. Since mRNA technology allows for faster vaccine development, scientists can quickly update the vaccine formula to target emerging new variants.

Can I get my COVID and flu vaccines at the same time?

Yes, you can get your COVID vaccine and flu shot at the same time. Many providers now offer both immunizations during a single visit, and CDC confirms it’s safe to get both. You can even receive your vaccines in the same arm (but injection sites should be at least one inch apart).

Getting your COVID and flu shots together saves time and ensures you’re protected against both viruses as flu season and potential COVID waves approach. Side effects from these vaccines tend to be mild. But if you’ve experienced adverse reactions in the past, and you’re worried about potential side effects from getting two shots at once, check with your health care provider first.

Are flu shots free? Where can I get mine?

Many recommended preventive vaccines for older adults are now 100% covered by Medicare and Medicaid—so you should pay nothing at your visit. Most private health insurance plans offer this coverage as well.

You can get your flu shot and COVID vaccine at your doctor’s office, pharmacies, community vaccine clinics, and many senior centers. You may have to register online and reserve a time slot ahead of time. 

For help finding nearby flu, COVID, and RSV vaccination sites:

• Talk to your primary health care provider.
• Dial 211 or reach out to your state health department.
• Reach out to organizations that support older adults or people with disabilities:
  • The Aging Network: 1-800-677-1116
  • Eldercare Locator: Search by ZIP code at eldercare.acl.gov
  • Disability Information and Access Line (DIAL): 1-888-677-1199 or email DIAL@n4a.org
  • Medicare hotline: 1-800-633-4227 (TTY 1-877-486-2048)

Frequently asked questions (FAQ)

Is August too early to get a flu shot?
Yes—for most adults, August is generally too early. Flu vaccine protection can decrease over time, so CDC recommends that most people get the flu shot in September or October.

What is the new mRNA flu vaccine?
mFLUSIVA is the first mRNA flu vaccine approved in the U.S. Made by Moderna, it uses the same type of mRNA technology used in some COVID-19 vaccines received by millions of people. In clinical trials, mFLUSIVA provided better protection against flu than a standard-dose flu vaccine and produced a stronger immune response than a high-dose flu vaccine.

mFLUSIVA is approved for adults age 50 and older and is expected to be available for the 2026–2027 flu season. It received accelerated approval for people 65+; more studies are being done to confirm the vaccine’s effectiveness in this age group.

When does flu season peak?
Flu activity usually increases during the fall and winter. While the timing varies from year to year, flu season most often peaks between December and February. This is one reason experts recommend getting your flu shot by the end of October, before flu activity typically reaches its highest levels.

Sources

1. CDC Morbidity and Mortality Weekly Report. Influenza-Associated Hospitalizations During a High Severity Season — Influenza Hospitalization Surveillance Network, United States, 2024–25 Influenza Season. September 11, 2025. Found on the internet at https://www.cdc.gov/mmwr/volumes/74/wr/mm7434a1.htm

2. CDC Flu Burden. 2024–2025 Influenza Season Summary: Severity, Disease Burden, and Burden Prevented. March 12, 2026. Found on the internet at https://www.cdc.gov/flu-burden/php/data-vis-vac/2024-2025-prevented.html

3. National Vital Statistics System. Mortality in the United States: Provisional Data, 2025. July 2026. Found on the internet at https://www.cdc.gov/nchs/data/vsrr/vsrr044.pdf

4. Centers for Disease Control and Prevention. Flu & People 65 Years and Older. Found on the internet at https://www.cdc.gov/flu/highrisk/65over.htm

5. CDC Morbidity and Mortality Weekly Report. Interim Estimates of 2025–26 Seasonal Influenza Vaccine Effectiveness — United States, September 2025–February 2026. March 12, 2026. Found on the internet at https://www.cdc.gov/mmwr/volumes/75/wr/mm7509a2.htm

6. Isabel Leroux-Roels, MD, et. al. Efficacy and safety of an mRNA seasonal influenza vaccine in adults. The New England Journal of Medicine. May 6, 2026. Found on the internet at https://www.nejm.org/doi/full/10.1056/NEJMoa2516491