The cold, crisp air of wintertime is the perfect excuse to put on that cozy sweater. Unfortunately, it also creates the perfect conditions for viruses to spread. That’s why fall is a good time to think about protecting ourselves from the flu—a highly contagious respiratory infection caused by the influenza virus.

How serious is the threat of flu every year? This virus can infect the nose, throat, and sometimes the lungs and can limit your daily activities and quality of life. Children and older adults (age 65+) are most at risk for developing severe flu illness and complications. According to the Centers for Disease Control and Prevention (CDC), the 2023-2024 flu season resulted in 380,000 flu-related hospitalizations and 17,000 deaths. People age 65 and older accounted for 51% of hospitalizations and 68% of deaths.¹

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.

What months are flu season?

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. However, 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.

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 2024-2025 flu shot effective?

Seasonal flu vaccines are reformulated every year to protect against the influenza strains scientists think are most likely to circulate. All 2024-2025 flu vaccines in the U.S. are "trivalent," which means they offer protection against three specific flu A and flu B viruses: an influenza A(H1N1) virus, an influenza A(H3N2) virus, and an influenza B/Victoria virus.

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. However, even if vaccine effectiveness falls below this range, 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.

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 before, you might wonder if you’re still protected. Immunity from a flu infection can last for a few months; in other words, you’ll likely be immune to the strain that infected you for the rest of flu season.

“But don’t forget there are different strains of the flu—and immunity from one infection doesn’t necessarily protect you from another strain that’s circulating,” explained Kathleen Cameron, former Senior Director of NCOA’s Center for Healthy Aging. “That’s why it’s so important to get your flu shot every year. It boosts your immunity against the specific strains that are prevailing out in the community.”

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 6 months and older get a flu shot, especially older adults and others at higher risk for complications. An annual flu shot helps you maintain optimal immunity, so 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.

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.

What about a vaccine that protects you against the flu and COVID? It may be here soon. While not yet available to the public, an mRNA-based combination vaccine against flu and COVID is now being developed and tested. If “mRNA” sounds familiar, it’s the technology behind two groundbreaking COVID vaccines (mRNA vaccines) that offer a high level of protection against the virus.

Are flu shots free? Where can I get mine?

All recommended 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. Find nearby flu vaccination sites by entering your ZIP code at Vaccines.gov.

Sources

1. Centers for Disease Control and Prevention (CDC) - Influenza (Flu). Influenza Activity in the United States during the 2023–2024 Season and Composition of the 2024–2025 Influenza Vaccine. Found on the internet at https://www.cdc.gov/flu/whats-new/flu-summary-2023-2024.html