Table of ContentsView AllTable of ContentsEffectiveness NowReasons to Get a ShotEfficacy FactorsTypesEffectiveness Over TimeSide EffectsFrequently Asked Questions
Table of ContentsView All
View All
Table of Contents
Effectiveness Now
Reasons to Get a Shot
Efficacy Factors
Types
Effectiveness Over Time
Side Effects
Frequently Asked Questions
The vaccine also reduces the likelihood of severe illness, hospitalization, and death. Because of this, the Centers for Disease Control and Prevention (CDC) recommends that everyone ages 6 months and over gets the flu vaccine (with very rare exceptions).Various different flu vaccines are available, but all of them protect against the same strains of flu. Here’s what you should know about flu vaccine effectiveness and types of flu vaccines.
Verywell / Theresa Chiechi
Flu Vaccine Effectiveness for 2023–2024 Season
Each year, the flu vaccine is designed to protect against the flu strains that scientists believe will be most common. However, the effectiveness of the flu vaccine depends on which flu strains are most prevalent and how they compare to the strains that the vaccine protects against.
Because of this, flu vaccine effectiveness varies from year to year. Scientists don’t yet have final estimates for the effectiveness of the flu vaccine for the 2023–2024 season, but preliminary data show a range of 33%-49% effectiveness in adults.
Flu Tests: Who Should Test and When?
During Past Flu Seasons
The CDC tracks seasonal flu vaccine effectiveness each year. Over the past 17 years, the highest effectiveness was in the 2010-2011 season, when it was 60% effective.
Here are the effectiveness rates over the past six seasons for which data are available:
During the 2020–2021 flu season, the CDC didn’t estimate the effectiveness of the vaccine because transmission of the flu was historically low, likely due to COVID-19 precautions that also protect against the flu.
What to Avoid After Flu Shot (and Do Instead)
Reasons to Consider Getting a Flu Vaccine
The flu vaccine (flu shot or nasal spray vaccine) significantly reduces the risk of contracting the flu. Consider the 2019–2020 season: People who had the vaccine were 39% less likely to get the flu than those who did not.
In addition to preventing illness, the flu vaccine also reduces the risk of hospitalization and death. Here’s what researchers have found about the flu vaccine:
In addition to protecting you, getting the flu vaccine can keep you from contracting the flu and passing it to others, including infants and the elderly, who are at higher risks for complications.
Can a Rash Be a Symptom of the Flu?
Flu Vaccine Efficacy Factors
There are a number of factors that influence how effective the flu vaccine is every year. The most important is strain matching—whether the strains that the vaccine protects against match the most widely circulating flu strains during a given season.
In addition to the construction of the vaccine, there are more personal factors that influence vaccine effectiveness.
Strain Matching
For the Northern Hemisphere, the WHO makes a recommendation in February. In the United States, the Food and Drug Administration (FDA) has the final say in which strains are included in the vaccine.
The decision about which strains to include is based on projections that are made using past data. This gives time to manufacture the vaccine.
Vaccine Timing
It takes two weeks for the flu vaccine to become optimally effective. Because of that, the CDC recommends that all people get the flu vaccine during September or October, before flu infections become widespread.
Getting the vaccine too late can leave you exposed to early infection from the flu. On the other hand, vaccine protection begins to wane after several months. Adults ages 65 and older are generally not vaccinated early (July or August) due to this.
Age
CDC data show that within a given year, the protection that the flu vaccine offers can vary based on age due to immune changes over time.There’s no way to predict which age groups the flu vaccine will be most or least effective for in a given season.
The CDC recommends that people age 65 and older receive a higher-dose or adjuvanted flu vaccine.
Health
If a person has an impaired immune system due to a health condition, they may not mount the desired immune response, reducing the vaccine’s effectiveness. There are a wide variety of health conditions that can impair your immune system response.
This is one reason that everyone should be vaccinated. By having less risk of getting and spreading the flu, they protect those who have impaired immunity and, therefore, can’t benefit as much from vaccinating themselves.
Types of Flu Shots and Vaccines
All flu vaccines protect against the same strains of flu. In 2024, the FDA reduced the number of strains included in the vaccine from four to three, because one of the previously included strains hasn’t been detected since 2020. Because the vaccines protect against three they are calledtrivalentvaccines.
The CDC doesn’t recommend one type of vaccine over the others. However, some people, including people under the age of 2, over the age of 65, who have allergies, or are pregnant, have special considerations and should talk to their doctor about which vaccine is best.
Adults 65 and Up
Some studies indicate that a higher-dose vaccine or an adjuvanted flu vaccine (one with an additional substance called an adjuvant that enhances the body’s immune response to an antigen) creates a stronger immune response) produce a stronger immune response and are therefore more effective for this population.
The CDC recommends people age 65 and older receive a higher-dose vaccine or an adjuvanted flu vaccine (one with an additional substance called an adjuvant that enhances the body’s immune response to an antigen). Three vaccines are specifically recommended for this population:
Senior Flu Shots
If You’re Allergic
According to the CDC, people who have severe allergies to an ingredient in the flu vaccine or who have had a severe reaction to the flu vaccine should not get a flu shot.
Most flu vaccines are made using eggs or egg protein, but the CDC states that people with egg allergies can get any flu vaccine, regardless of the severity of their allergy. The CDC previously had recommended that people with egg allergies should get their flu shots in an inpatient or outpatient setting. For those interested in an egg-free flu shot, the two egg-free vaccine options are:
New or Ongoing Egg Allergy Symptoms
If You’re Pregnant
Pregnant people can get any flu vaccineexceptfor FluMist, which contains a live virus.
Study Shows Flu Shot in Pregnancy Does Not Lead to Health Issues for Children
Nasal Spray Option
What Is the FluMist Flu Vaccine?
Flu Vaccine for Babies
There are five flu vaccines approved for babies 6 months and older. They are:
Flu Vaccine Effectiveness Over Time
The flu vaccine needs two weeks to become fully effective, and protection is thought to last for at least six months.But a person’s antibody levels in response to the vaccine can decrease over time, and different flu strains may be circulating.
Because of that and because each year the vaccine is tailored to the most concerning flu variants, people should get a flu vaccine annually.
Flu Vaccine Side Effects
Side effects of the flu vaccineare usually mild and go away without treatment in a few days. Common side effects include:
Rarely,allergic reactionsoccur, often within minutes of the vaccine being administered. If you experience swelling, racing heart or trouble breathing, seek medical attention immediately. Extremely rarely (no more than one or two cases per million people who receive the flu vaccine) a person may developGuillain-Barré syndrome, an autoimmune disease.
The Most Common and Rare Flu Shot Side Effects
Summary
The flu vaccine can prevent illness, hospitalization, and death. The CDC recommends that everybody aged 6 months and older get the vaccine every year (with very rare exceptions). The effectiveness of the vaccine varies since the vaccine only protects against certain strains of flu. Over the past five years, the effectiveness of the flu vaccine has ranged from 29%–40%.
A Word From Verywell
Deciding whether to vaccinate can be a big decision. Although the flu is a common illness, it can be deadly, particularly for people over the age of 65. The flu vaccine isn’t 100% effective, but it does significantly reduce the risk of illness, hospitalization, and death.
If you have questions about the vaccine, talk to your doctor about whether it is right for you or your children.
Frequently Asked QuestionsThe flu vaccine first became available in the 1930s, and it became widely available in 1945.Flu vaccine effectiveness varies from year to year. It depends on how well the strains in the vaccine match the strains that are most prevalent in a given year.Yes, the CDC says that the flu vaccine and COVID-19 vaccine, including boosters, can be administered at the same time.Learn MoreGetting a Flu Shot and COVID Vaccine TogetherThe flu shot is made with either killed or weakened flu virus. The shots also contain inactive ingredients, including preservatives.
The flu vaccine first became available in the 1930s, and it became widely available in 1945.
Flu vaccine effectiveness varies from year to year. It depends on how well the strains in the vaccine match the strains that are most prevalent in a given year.
Yes, the CDC says that the flu vaccine and COVID-19 vaccine, including boosters, can be administered at the same time.Learn MoreGetting a Flu Shot and COVID Vaccine Together
Yes, the CDC says that the flu vaccine and COVID-19 vaccine, including boosters, can be administered at the same time.
Learn MoreGetting a Flu Shot and COVID Vaccine Together
The flu shot is made with either killed or weakened flu virus. The shots also contain inactive ingredients, including preservatives.
16 SourcesVerywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read oureditorial processto learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.Centers for Disease Control and Prevention.CDC seasonal flu vaccine effectiveness studies.Centers for Disease Control and Prevention.Past seasons’ vaccine effectiveness estimates.Grohskopf LA, Blanton LH, Ferdinands JM, et al.Prevention and control of seasonal influenza with vaccines: recommendations of the Advisory Committee on Immunization Practices - United States, 2022-23 influenza season.MMWR Recomm Rep. 2022;71(1):1-28. doi:10.15585/mmwr.rr7101a1Centers for Disease Control and Prevention.Interim Estimates of 2023–24 Seasonal Influenza Vaccine Effectiveness — United States.Ferdinands JM, Thompson MG, Blanton L, Spencer S, Grant L, Fry AM.Does influenza vaccination attenuate the severity of breakthrough infections? A narrative review and recommendations for further research.Vaccine. 2021;39(28):3678-3695. doi:10.1016/j.vaccine.2021.05.011Thompson MG, Pierse N, Sue Huang Q, et al.Influenza vaccine effectiveness in preventing influenza-associated intensive care admissions and attenuating severe disease among adults in New Zealand 2012–2015.Vaccine. 2018;36(39):5916-5925. doi:10.1016/j.vaccine.2018.07.028Udell JA, Zawi R, Bhatt DL, et al.Association between influenza vaccination and cardiovascular outcomes in high-risk patients: a meta-analysis.JAMA. 2013;310(16):1711-20. doi:10.1001/jama.2013.279206Immunization Action Coalition.Influenza.Centers for Disease Control and Prevention.Selecting viruses for the seasonal influenza vaccine.Centers for Disease Control and Prevention.Key facts about seasonal flu vaccine.Centers for Disease Control and Prevention.US flu VE data for 2019-2020.Centers for Disease Control and Prevention.US Will Transition to Trivalent Flu Vaccines for 2024-2025.Centers for Disease Control and Prevention.Who Should and Who Should NOT Get a Flu Vaccine.Centers for Disease Control and Prevention.Quadrivalent influenza vaccine.Centers for Disease Control and Prevention.Frequently asked questions about COVID-19 vaccination.Centers for Disease Control and Prevention.What’s in vaccines?
16 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read oureditorial processto learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.Centers for Disease Control and Prevention.CDC seasonal flu vaccine effectiveness studies.Centers for Disease Control and Prevention.Past seasons’ vaccine effectiveness estimates.Grohskopf LA, Blanton LH, Ferdinands JM, et al.Prevention and control of seasonal influenza with vaccines: recommendations of the Advisory Committee on Immunization Practices - United States, 2022-23 influenza season.MMWR Recomm Rep. 2022;71(1):1-28. doi:10.15585/mmwr.rr7101a1Centers for Disease Control and Prevention.Interim Estimates of 2023–24 Seasonal Influenza Vaccine Effectiveness — United States.Ferdinands JM, Thompson MG, Blanton L, Spencer S, Grant L, Fry AM.Does influenza vaccination attenuate the severity of breakthrough infections? A narrative review and recommendations for further research.Vaccine. 2021;39(28):3678-3695. doi:10.1016/j.vaccine.2021.05.011Thompson MG, Pierse N, Sue Huang Q, et al.Influenza vaccine effectiveness in preventing influenza-associated intensive care admissions and attenuating severe disease among adults in New Zealand 2012–2015.Vaccine. 2018;36(39):5916-5925. doi:10.1016/j.vaccine.2018.07.028Udell JA, Zawi R, Bhatt DL, et al.Association between influenza vaccination and cardiovascular outcomes in high-risk patients: a meta-analysis.JAMA. 2013;310(16):1711-20. doi:10.1001/jama.2013.279206Immunization Action Coalition.Influenza.Centers for Disease Control and Prevention.Selecting viruses for the seasonal influenza vaccine.Centers for Disease Control and Prevention.Key facts about seasonal flu vaccine.Centers for Disease Control and Prevention.US flu VE data for 2019-2020.Centers for Disease Control and Prevention.US Will Transition to Trivalent Flu Vaccines for 2024-2025.Centers for Disease Control and Prevention.Who Should and Who Should NOT Get a Flu Vaccine.Centers for Disease Control and Prevention.Quadrivalent influenza vaccine.Centers for Disease Control and Prevention.Frequently asked questions about COVID-19 vaccination.Centers for Disease Control and Prevention.What’s in vaccines?
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read oureditorial processto learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
Centers for Disease Control and Prevention.CDC seasonal flu vaccine effectiveness studies.Centers for Disease Control and Prevention.Past seasons’ vaccine effectiveness estimates.Grohskopf LA, Blanton LH, Ferdinands JM, et al.Prevention and control of seasonal influenza with vaccines: recommendations of the Advisory Committee on Immunization Practices - United States, 2022-23 influenza season.MMWR Recomm Rep. 2022;71(1):1-28. doi:10.15585/mmwr.rr7101a1Centers for Disease Control and Prevention.Interim Estimates of 2023–24 Seasonal Influenza Vaccine Effectiveness — United States.Ferdinands JM, Thompson MG, Blanton L, Spencer S, Grant L, Fry AM.Does influenza vaccination attenuate the severity of breakthrough infections? A narrative review and recommendations for further research.Vaccine. 2021;39(28):3678-3695. doi:10.1016/j.vaccine.2021.05.011Thompson MG, Pierse N, Sue Huang Q, et al.Influenza vaccine effectiveness in preventing influenza-associated intensive care admissions and attenuating severe disease among adults in New Zealand 2012–2015.Vaccine. 2018;36(39):5916-5925. doi:10.1016/j.vaccine.2018.07.028Udell JA, Zawi R, Bhatt DL, et al.Association between influenza vaccination and cardiovascular outcomes in high-risk patients: a meta-analysis.JAMA. 2013;310(16):1711-20. doi:10.1001/jama.2013.279206Immunization Action Coalition.Influenza.Centers for Disease Control and Prevention.Selecting viruses for the seasonal influenza vaccine.Centers for Disease Control and Prevention.Key facts about seasonal flu vaccine.Centers for Disease Control and Prevention.US flu VE data for 2019-2020.Centers for Disease Control and Prevention.US Will Transition to Trivalent Flu Vaccines for 2024-2025.Centers for Disease Control and Prevention.Who Should and Who Should NOT Get a Flu Vaccine.Centers for Disease Control and Prevention.Quadrivalent influenza vaccine.Centers for Disease Control and Prevention.Frequently asked questions about COVID-19 vaccination.Centers for Disease Control and Prevention.What’s in vaccines?
Centers for Disease Control and Prevention.CDC seasonal flu vaccine effectiveness studies.
Centers for Disease Control and Prevention.Past seasons’ vaccine effectiveness estimates.
Grohskopf LA, Blanton LH, Ferdinands JM, et al.Prevention and control of seasonal influenza with vaccines: recommendations of the Advisory Committee on Immunization Practices - United States, 2022-23 influenza season.MMWR Recomm Rep. 2022;71(1):1-28. doi:10.15585/mmwr.rr7101a1
Centers for Disease Control and Prevention.Interim Estimates of 2023–24 Seasonal Influenza Vaccine Effectiveness — United States.
Ferdinands JM, Thompson MG, Blanton L, Spencer S, Grant L, Fry AM.Does influenza vaccination attenuate the severity of breakthrough infections? A narrative review and recommendations for further research.Vaccine. 2021;39(28):3678-3695. doi:10.1016/j.vaccine.2021.05.011
Thompson MG, Pierse N, Sue Huang Q, et al.Influenza vaccine effectiveness in preventing influenza-associated intensive care admissions and attenuating severe disease among adults in New Zealand 2012–2015.Vaccine. 2018;36(39):5916-5925. doi:10.1016/j.vaccine.2018.07.028
Udell JA, Zawi R, Bhatt DL, et al.Association between influenza vaccination and cardiovascular outcomes in high-risk patients: a meta-analysis.JAMA. 2013;310(16):1711-20. doi:10.1001/jama.2013.279206
Immunization Action Coalition.Influenza.
Centers for Disease Control and Prevention.Selecting viruses for the seasonal influenza vaccine.
Centers for Disease Control and Prevention.Key facts about seasonal flu vaccine.
Centers for Disease Control and Prevention.US flu VE data for 2019-2020.
Centers for Disease Control and Prevention.US Will Transition to Trivalent Flu Vaccines for 2024-2025.
Centers for Disease Control and Prevention.Who Should and Who Should NOT Get a Flu Vaccine.
Centers for Disease Control and Prevention.Quadrivalent influenza vaccine.
Centers for Disease Control and Prevention.Frequently asked questions about COVID-19 vaccination.
Centers for Disease Control and Prevention.What’s in vaccines?
Meet Our Medical Expert Board
Share Feedback
Was this page helpful?Thanks for your feedback!What is your feedback?OtherHelpfulReport an ErrorSubmit
Was this page helpful?
Thanks for your feedback!
What is your feedback?OtherHelpfulReport an ErrorSubmit
What is your feedback?
