Table of ContentsView AllTable of ContentsWhen to Get ItFlu SeasonBuilding ImmunityDifferent StrainsOverall Effectiveness
Table of ContentsView All
View All
Table of Contents
When to Get It
Flu Season
Building Immunity
Different Strains
Overall Effectiveness
The annual flu shot protects against influenza for up to six months.The Centers for Disease Control and Prevention (CDC) recommends a yearly influenza vaccine for everyone 6 months and older. For most groups, it’s best to get the shot in September or October.
Properly timing your flu shot can help to ensure the vaccine is effective during the peak of flu season. It takes about two weeks to build your immunity after getting the flu shot.
This article explains how long a flu shot lasts and why. It also discusses the best time to get your flu shot and why you need a new one each year.
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When Should I Get a Flu Shot?
The CDC currently recommends most adults get the flu shot in September or October. This helps ensure that you’re vaccinated before peak flu season starts and that the protection will last through spring.
The main exception to the rule is pregnant people in their third trimester. They can get the vaccine in July or August to protect their babies from flu after birth.Certain children can also receive the vaccine earlier (see below).
For everyone else, getting vaccinated earlier in the season is no longer routinely recommended. The influenza vaccine’s effectiveness starts to wane after five or six months.A July or August flu shot may not keep you protected through the end of the winter.
If you miss the end of October deadline, though, it’s not too late. The worst of flu season is still ahead, so it’s still worthwhile to get the shot in January or even later.
When Should Children Get a Flu Shot?Children between 6 months and 8 years old should get the influenza vaccine annually in September or October. However, children who get the flu vaccine for the first time (or who only had one dose of the vaccine in total from previous years) will need two doses at least a month apart. The CDC recommends these children receive the first dose as soon as the vaccine becomes available, typically in July or August.
When Should Children Get a Flu Shot?
Children between 6 months and 8 years old should get the influenza vaccine annually in September or October. However, children who get the flu vaccine for the first time (or who only had one dose of the vaccine in total from previous years) will need two doses at least a month apart. The CDC recommends these children receive the first dose as soon as the vaccine becomes available, typically in July or August.
When Is Flu Season?
However, in 2022, the CDC updated its recommendations to note that the timing of flu activity is difficult to predict and can vary in different parts of the country and from season to season.
Flu activity can ramp up earlier or later in different parts of the country. For example, in Tennessee, the 2022 flu season began in late September, with high pediatric hospitalizations reported in November.
How Long Does the Flu Shot Take to Work?
It takes time for your body to create antibodies, though, and they don’t last forever.
The flu vaccine takes about two weeks to fully take effect.The number of antibodies in your immune system starts to decline after about five or six months.
Who Should Not Get Flu Shots?
Changing Flu Strains
Aside from the fact that the flu vaccine is only effective for several months, yearly flu vaccination is necessary because the strains of influenza included usually differ from flu season to flu season.
The most common types of seasonal flu, which are also the most serious, mutate quickly.
Researchers work hard each year to determine what strains of influenza are likely to cause illness the following flu season. Starting with the 2024-2025 season, the vaccine will include two strains of influenza A and one strain of influenza B.
Although it doesn’t typically change drastically, the vaccine usually varies slightly from one year to the next to account for new strains.
Are You At-Risk for Flu Complications?
How Effective Are Flu Vaccines?
The effectiveness of flu vaccines, like their composition, varies from year to year. If the strains of influenza included in the vaccine are well matched to the strains causing illness in the community, the vaccine will be more effective than if they aren’t.
Remember, though, that the vaccine is not a guarantee that you won’t get sick. Even if it works well, it won’t protect you from every illness—only influenza.
Summary
The flu shot protects against the influenza virus for about six months. The CDC recommends most adults get the annual flu shot in September or October. Children under age 8 who need two doses of the vaccine should get the first in the series in July or August.
8 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.National Center for Immunization and Respiratory Diseases.Ask the Experts: Influenza.Centers for Disease Control and Prevention.CDC Recommends Updated 2024-2025 COVID-19 and Flu Vaccines for Fall/Winter Virus Season.Centers for Disease Control and Prevention.Frequently asked influenza (flu) questions: 2022-2023 season.Centers for Disease Control and Prevention.Who needs a flu vaccine?Thomas CM, White EB, Kojima N, et al.Early and Increased Influenza Activity Among Children — Tennessee, 2022–23 Influenza Season.MMWR Morb Mortal Wkly Rep. 2023;72:49–54. doi:10.15585/mmwr.mm7203a1Centers for Disease Control and Prevention.Selecting viruses for the seasonal influenza vaccine.Centers for Disease Control and Prevention.US Will Transition to Trivalent Flu Vaccines for 2024-2025.Centers for Disease Control and Prevention.Vaccine Effectiveness: How Well Do the Flu Vaccines Work?Additional ReadingCenters for Disease Control and Prevention.Key facts about flu vaccines.
8 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.National Center for Immunization and Respiratory Diseases.Ask the Experts: Influenza.Centers for Disease Control and Prevention.CDC Recommends Updated 2024-2025 COVID-19 and Flu Vaccines for Fall/Winter Virus Season.Centers for Disease Control and Prevention.Frequently asked influenza (flu) questions: 2022-2023 season.Centers for Disease Control and Prevention.Who needs a flu vaccine?Thomas CM, White EB, Kojima N, et al.Early and Increased Influenza Activity Among Children — Tennessee, 2022–23 Influenza Season.MMWR Morb Mortal Wkly Rep. 2023;72:49–54. doi:10.15585/mmwr.mm7203a1Centers for Disease Control and Prevention.Selecting viruses for the seasonal influenza vaccine.Centers for Disease Control and Prevention.US Will Transition to Trivalent Flu Vaccines for 2024-2025.Centers for Disease Control and Prevention.Vaccine Effectiveness: How Well Do the Flu Vaccines Work?Additional ReadingCenters for Disease Control and Prevention.Key facts about flu 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.
National Center for Immunization and Respiratory Diseases.Ask the Experts: Influenza.Centers for Disease Control and Prevention.CDC Recommends Updated 2024-2025 COVID-19 and Flu Vaccines for Fall/Winter Virus Season.Centers for Disease Control and Prevention.Frequently asked influenza (flu) questions: 2022-2023 season.Centers for Disease Control and Prevention.Who needs a flu vaccine?Thomas CM, White EB, Kojima N, et al.Early and Increased Influenza Activity Among Children — Tennessee, 2022–23 Influenza Season.MMWR Morb Mortal Wkly Rep. 2023;72:49–54. doi:10.15585/mmwr.mm7203a1Centers for Disease Control and Prevention.Selecting viruses for the seasonal influenza vaccine.Centers for Disease Control and Prevention.US Will Transition to Trivalent Flu Vaccines for 2024-2025.Centers for Disease Control and Prevention.Vaccine Effectiveness: How Well Do the Flu Vaccines Work?
National Center for Immunization and Respiratory Diseases.Ask the Experts: Influenza.
Centers for Disease Control and Prevention.CDC Recommends Updated 2024-2025 COVID-19 and Flu Vaccines for Fall/Winter Virus Season.
Centers for Disease Control and Prevention.Frequently asked influenza (flu) questions: 2022-2023 season.
Centers for Disease Control and Prevention.Who needs a flu vaccine?
Thomas CM, White EB, Kojima N, et al.Early and Increased Influenza Activity Among Children — Tennessee, 2022–23 Influenza Season.MMWR Morb Mortal Wkly Rep. 2023;72:49–54. doi:10.15585/mmwr.mm7203a1
Centers for Disease Control and Prevention.Selecting viruses for the seasonal influenza vaccine.
Centers for Disease Control and Prevention.US Will Transition to Trivalent Flu Vaccines for 2024-2025.
Centers for Disease Control and Prevention.Vaccine Effectiveness: How Well Do the Flu Vaccines Work?
Centers for Disease Control and Prevention.Key facts about flu vaccines.
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