Should You Get the Flu Shot, and How Often Do You Need One?
Key takeaways:
The yearly flu shot saves lives and prevents serious illness.
You need to get a new flu shot each year to stay protected from changes to the flu virus.
The flu shot protects you and the people close to you who may be at risk for serious complications from the flu.
The flu (influenza) is a respiratory virus that circulates each year, typically in the colder months that make up flu season. It causes mild illness for some people, but it can cause serious illness and death for others.
Getting a yearly flu shot is the best way to protect yourself from the flu. It saves lives every year by preventing people from catching the flu and by making the illness less serious for people who do get sick. The flu virus changes (mutates) easily, and different versions (strains) of the flu virus circulate yearly.
So, how often should you get a flu shot? The answer is straightforward. Just about everyone should get an updated flu shot every year.
Why is it recommended to get a flu shot every year?
The influenza virus spreads easily through communities. It floats through the air in water droplets, and it sticks to surfaces you might touch. If the virus gets inside your body, it can make you sick.
Part of the flu virus stays the same every year. But other parts of the virus change as the virus spreads from person to person.
Since the flu virus changes all the time, the flu shot needs to change too. This means that the flu shot you got last year won’t protect you against this year’s flu virus.
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Plus, the immune defenses (antibodies) your body makes in response to the flu vaccine weaken with time. So, even if the flu virus strains didn’t change from year to year, you would still need regular flu vaccine boosters to keep your defenses strong.
Will you always need to get the flu shot every year?
Hopefully not. Research is ongoing to create a universal flu shot. This universal flu vaccine would, in theory, help your body create antibodies against the part of the flu virus that doesn’t change every year.
Right now, yearly vaccines target those proteins on the surface of the flu virus that change throughout the flu season. A new universal vaccine would protect you against current strains of the flu virus as well as future mutations of the flu virus.
Why do healthy people need the flu shot?
Healthy people should get vaccinated against the flu vaccine every year because anyone can get seriously ill from the flu. Some groups have a higher risk than others.
But the flu vaccine helps prevent serious illness and death from the flu in all people who get vaccinated. It also reduces the spread of the flu to people who can’t get vaccinated. The more people who get the flu vaccine, the more everyone in our communities is protected.
How effective are flu shots?
The flu shot is typically about 40% to 60% effective at preventing flu infections. But exactly how effective the flu shot is in a given year depends on how well the circulating flu virus matches the vaccine.
Does the flu shot actually work? Yes, the flu vaccine is effective and the best way to protect yourself from the flu.
Can kids get a flu shot if they have a cold? Yes, most kids can still get a flu shot if they have a mild illness like a cold. A pediatrician shares the details.
Where to get a flu test: A flu test is a sure way to know whether you have the flu. Here’s where to get one now.
Why does the flu shot’s effectiveness vary so much?
The effectiveness of the flu shot has a bit to do with timing and educated guessing. This is because public health scientists and flu virus researchers have to predict 6 months in advance what they think the next year’s flu virus will look like.
You might be wondering how scientists make these predictions. Around February of each year, experts with the World Health Organization (WHO) review data from the last flu season to make an educated guess about which strains are most likely to circulate during the next flu season.
These experts then recommend which strains should be covered in the new flu shot. This gives the flu shot manufacturers the 6 months that they need to prepare the new flu shot. In late summer, the seasonal flu shot is typically ready to be given out.
In some seasons, the prediction of the strains matches the reality of the strains spreading in the community. When this happens, the vaccine is very effective. In other seasons, the flu virus may change, and strains that aren’t covered by the vaccine may cause the most illness. In these seasons, the flu shot is less effective.
Quiz: Test your flu shot knowledge
How long does flu shot immunity last?
This is unclear, and research is ongoing. In one study of younger adults (18 to 49 years old), flu antibodies decreased slowly over 18 months after they got their shots. Another study of the same age group showed that antibody levels remained high enough to be effective throughout the whole flu season, or 5 to 6 months after vaccination.
When is the best time of year to get a flu shot?
You should get the flu shot each year at least 2 weeks before the flu virus starts spreading in your community. In the Northern Hemisphere (where the U.S. is located), the flu shot typically becomes available around September of each year.
The CDC recommends getting the flu vaccine no earlier than September and no later than the end of October. Basically, you want to time it just right so that you’re fully vaccinated when the flu virus starts to circulate. But you don’t want to be too early so that your immunity runs out before the end of the flu season (which can last as late as May). You can still get the flu in summer, but this is less likely to happen.
Who should not get a yearly flu shot?
Almost everyone should get a yearly flu shot. The only reason not to get the standard flu shot is if you’ve had a severe reaction to the flu shot or any components of the flu shot in the past.
There are other versions of the flu vaccine (like the flu vaccine that you can get as a nasal spray) that have different guidelines. Check out our article on flu vaccine options and ingredients.
Who should not get the ‘senior’ flu shot?
There are certain flu shots that are available only to people 65 years old and older. The flu presents a great risk for older adults, and high-dose flu vaccines provide more protection than the standard flu shot. But if one of the high-dose flu shots isn’t available, it’s OK to get a regular flu shot.
Frequently asked questions
The flu shot can cause some short-lived side effects that can make you feel sick. This is a normal reaction and a sign that your immune system is making antibodies to help prevent future infections. But you can't get the flu from the flu vaccine. Some people can have an allergic reaction to the flu shot, but this is rare.
Yes, you can get a flu shot if you have a mild illness, like a common cold or other upper respiratory tract infection. But if you aren’t sure what’s causing your symptoms, it’s best to check with your primary care provider. They may recommend that you reschedule your flu shot until your symptoms have improved.
No, a regular flu shot doesn’t give you protection against bird flu viruses. But the CDC is working on developing a vaccine against bird flu to be prepared in case it’s necessary in the future. For now, the best way to protect against bird flu is to avoid coming into contact with wild birds and to thoroughly cook poultry before eating it.
The bottom line
The yearly flu shot is safe and effective, and it saves lives. It also prevents you and the people around you from suffering from unnecessary illness. Everyone ages 6 months and older should get the flu shot every year.
Why trust our experts?
References
Adams, K., et al. (2021). A literature review of severity scores for adults with influenza or community-acquired pneumonia - implications for influenza vaccines and therapeutics. Human Vaccines and Immunotherapeutics.
Centers for Disease Control and Prevention. (2022). What are the benefits of flu vaccination?
Centers for Disease Control and Prevention. (2023). Who should and should NOT get a flu vaccine.
Centers for Disease Control and Prevention. (2024). Effectiveness against different flu viruses.
Centers for Disease Control and Prevention. (2024). Factors influencing flu vaccine effectiveness.
Centers for Disease Control and Prevention. (2024). Flu and people 65 years and older.
Centers for Disease Control and Prevention. (2024). Key facts about seasonal flu vaccine.
Centers for Disease Control and Prevention. (2024). Prevention and antiviral treatment of avian influenza A viruses in people.
Centers for Disease Control and Prevention. (2024). Who needs a flu vaccine?
Immunize.org. (n.d.). Search results for influenza.
Petrie, J. G., et al. (2015). Persistence of antibodies to influenza hemagglutinin and neuraminidase following one or two years of influenza vaccination. The Journal of Infectious Diseases.
Petrie, J. G., et al. (2016). Modest waning of influenza vaccine efficacy and antibody titers during the 2007-2008 influenza season. The Journal of Infectious Diseases.
Sautto, G. A., et al. (2018). Towards a universal influenza vaccine: Different approaches for one goal. Virology Journal.
U.S. Food and Drug Administration. (2024). Use of Trivalent influenza vaccines for the 2024-2025 U.S. influenza season.
