How Long Is the Flu Shot Good?

The flu — also known as influenza — can be a much more serious disease than most people realize. Depending on your age and current health, you may be at a greater risk of developing potentially serious complications from the flu.

According to the National Institutes of Health, more than 36,000 Americans die from the flu each year, and another 200,000 are hospitalized.

This is why the U.S. Centers for Disease Control and Prevention (CDC) recommends that every eligible person ages 6 months and older receive a flu vaccine—also known as the flu shot—every year.

Let's break down what the flu vaccine is, how it works, its potential side effects, and how long the flu shot is good for.

How Does the Flu Vaccine Work?

A vaccine works by training the body's immune system to identify a certain disease so it can recognize and defend against it. It does this by using dead or weakened forms of the disease—when they enter the body, the immune system creates antibodies to fight them. This "teaches" the body's immune system how to respond if it encounters that specific virus again.

The flu vaccine introduces dead influenza virus molecules into the body. After about two weeks, the body has antibodies against the flu during flu season.

All flu vaccines in the U.S. are trivalent, meaning they cover three different flu viruses in one shot. The 2024-2025 vaccine will include protection against influenza types A(H1N1) and A(H3N2) and B/Victoria-lineage virus.

A common question patients ask is how long the flu shot is good for. Because the strain of the influenza virus changes every year, the vaccine also needs to change, which means you do need to receive the vaccine every year.

When Does the Flu Vaccine Start Working?

It generally takes about two weeks after receiving the flu vaccine for the body to be completely protected against the flu virus.

Because you can still get the flu during those two weeks, it's important to get your flu shot before the start of the flu season, which in the U.S. normally runs from October through May. The CDC recommends most people receive their flu vaccine in September and October.

How Long Does the Flu Shot Last?

How long is the flu shot good for? It depends on your immune response, but the flu shot generally lasts six to eight months. That's why you don't want to get it too early or late into flu season.

After about the six-month mark, past research shows that the flu vaccine starts to fade. That's why it's important to update your flu shot every year and talk to your AdventHealth Centra Care provider about the best time to get a flu shot for the most protection during flu season.

When Should You Get Your Flu Shot?

When considering how long the flu shot is good for, the CDC suggests that every person ages 6 months and older who is eligible to receive the vaccine receive it in September or October and no later than the end of October.

Because the flu season normally begins in October, getting the vaccine in September and early October gives it two weeks to provide the best protection.

And since you will need to receive a flu shot every year to protect yourself from that year’s virus strains, we recommend scheduling a recurring calendar event every year in July or August to remind you to schedule that year’s vaccine appointment for September or early October.

There are a few cases in which a person can get their flu shot earlier.

For example, women in their third trimester of pregnancy in July or August can receive their flu shot during those months to ensure the flu antibodies are passed on to their baby when they are born during flu season.

Can You Get the Flu Shot Too Early or Too Late?

Generally, the flu season in the U.S. runs from October through May, with the most activity between December and February.

How long is the flu shot good for? Between six to eight months, its potency starts to fade after the sixth month. If you get your flu shot during the summer, you may have less protection during peak flu season.

Alternatively, receiving the flu shot too late may also leave you more vulnerable during the beginning of the flu season, as it takes two weeks to protect the body from the virus fully.

Do You Need to Get Another Flu Shot During the Same Flu Season?

The CDC says that almost everyone only needs to receive one dose of the flu vaccine each year.

While most people will receive standard-dose flu vaccines, there are higher-dose options for adults 65 years and older and those who are immunocompromised or have a weak immune system.

However, there are a few cases in which a person may need two doses of the flu vaccine.

• The CDC recommends that children ages 6 months to 8 years old who are receiving the flu vaccine for the first time receive two doses of the vaccine, with the second shot given at least four weeks after the first shot. Contact your local AdventHealth Centra Care urgent care to schedule your child’s pediatric flu shot.
• Research still debates whether immunocompromised people—such as those who have received organ transplants, are HIV positive, or are undergoing chemotherapy—should receive two doses of the flu vaccine. If you are an immunocompromised person, it's important to discuss your flu vaccine options with your doctor.

Who Should Get the Flu Shot, and Who Shouldn’t?

Generally speaking, the CDC advocates that every person in the U.S. who is 6 months of age and older receives a flu shot every year before flu season begins. If you ask your doctor how long the flu shot is good for, they will tell you about six to eight months.

Receiving an annual flu shot is especially important for those who have a high risk of developing complications from influenza, including:

• adults age 65 and older
• children younger than 2 years old
• pregnant women
• people with underlying medical conditions such as asthma, chronic lung disease, heart disease, obesity, and diabetes
• people living in long-term care facilities

As we age, our immune systems weaken, which can make older adults over 65 more susceptible to influenza and potentially develop serious complications.

The opposite is true for children under the age of 2, as their immune systems are not fully developed enough to fight off the flu.

The American College of Obstetricians and Gynecologists (ACOG) recommends pregnant cisgender women receive a flu shot as it can help protect them from the virus during pregnancy and when in the hospital during delivery.

Pregnant people can receive the flu vaccine in July or August if they are in their third trimester and they want to ensure their baby is born with flu protection as they will not be able to receive the vaccine until at least 6 months old.

There are also a few groups who should not receive the flu vaccine:

• children under 6 months of age
• anyone who has had a previous allergic reaction to the flu shot
• anyone with a known allergy to any ingredients in the influenza vaccine, such as gelatin or eggs
• people with Guillain-Barre syndrome

As of 2023, the CDC says that additional safety measures are no longer needed for people with egg allergies receiving a flu shot.

If you have any questions regarding whether it is safe to receive the flu vaccine, talk to your local AdventHealth Centra Care provider for guidance.

Factors That Affect Flu Shot Effectiveness

While the flu vaccine offers great protection against the flu virus, currently, it does not provide 100% protection. That means you can still get the flu even if you have had your flu shot.

The flu vaccine is normally 40% to 60% effective in protecting someone from the flu.

This is why it's important to understand how long the flu shot lasts to give yourself the best defense possible during peak flu season.

Every person is different, so the effectiveness of the flu shot in one person may not be the same in another. For example, age and underlying health can influence how well the flu vaccine works.

Additionally, because the flu virus is ever-changing, sometimes the types of dead or weakened flu virus in that year's vaccine may not fully match the most dominant flu strain. This can also impact the effectiveness of the vaccine.

How to Maximize Flu Shot Effectiveness

Because there are so many factors at play when it comes to the effectiveness of the flu vaccine, everyone needs to follow good flu prevention habits, such as:

• avoid close contact with people who are sick
• cover your mouth and nose when coughing or sneezing
• disinfect surfaces
• don't touch your eyes, nose, or mouth
• proper hand-washing
• stay home from work or school when sick

Other healthy habits that can also help keep the flu away include:

• eating a healthy diet
• exercising
• drinking lots of water
• getting enough sleep
• managing stress

And remember — although the flu is most common during the winter, you can get it all year round. So, even if you have already had the flu during the spring or summer, you can still get vaccinated for the winter.

Protect Your Family From the Flu This Year

How long is the flu shot good for? After six months, it begins to lose its potency, so timing is everything. The best way to keep you and your loved ones out of danger from the flu this winter season is by getting vaccinated.

Any member of your family who is 6 months or older — especially anyone at high risk for flu complications — should receive an influenza vaccine every year in September or October before flu season kicks off.

If you're considered a higher-risk individual, have had a recent respiratory illness, or have pre-existing health conditions, contact your health care provider about getting the seasonal flu vaccine this year.

If you have questions about the flu shot or wish to schedule your vaccine appointment, contact AdventHeath Centra Care today.