Each fall, medical experts recommend that nearly everyone 6 months and older be vaccinated against the flu — before flu season, which typically starts to ramp up in October, is in full swing.
But even though the flu shot has been around since the 1940s, and has been proven every year since to be the most effective way to prevent infection with the influenza virus, there are lots of misunderstandings and misconceptions about it.
Whether you’re a fan of the flu shot and never miss a season, you’re wary of it, you simply forget about it, or you figure you won’t get sick — and if you do, it won’t be so bad — learning all you can about the vaccine can help you make informed decisions about it going forward.
How Does the Flu Vaccine Work?
Which Flu Strains Does the Vaccine Protect Against?
The flu vaccine is updated every year to match the specific strains of the influenza virus experts predict will be most prominent during flu season. To determine this, the World Health Organization Global Influenza Surveillance Response System, made up of 144 influenza centers in 114 countries, conducts year-round surveillance to determine which flu strains are actively circulating around the globe.
Twice a year, representatives from five of the top participating centers come together to review data and recommend which strains to include in the upcoming flu vaccine.
“These flu experts try to anticipate what the dominant strains are going to be nine months down the road,” explains William Schaffner, MD, professor of infectious disease at Vanderbilt University School of Medicine in Nashville. “They're often on target, but on some occasions, the flu virus that circulates varies from the vaccine. How effective the influenza vaccine is changes from year to year too.”
In other words, flu virus experts have to base their recommendations on a moving target, which means the flu vaccine can’t be perfect. Even so, according to the Centers for Disease Control and Prevention (CDC), the most recent research suggests the flu shot lowers the risk of illness from 40 to 60 percent.
As for the specific influenza strains included in the flu vaccine, for the 2022-2023 season, there are four: two influenza A strains and two influenza B strains. In previous flu seasons, most vaccines protected against only three strains.
5 Essential Facts About the Flu Vaccine
1. There are several types of flu vaccine.
A wide variety of flu shots are available for the 2022–2023 flu season, all of which fall into one of the following categories, with the exception of the nasal mist:
- Standard unadjuvanted quadrivalent An egg-based vaccine for people 6 months and older
- Quadrivalent cell-based An egg-free vaccine for people 6 months and older
- Recombinant quadrivalent An egg-free vaccine for people 18 and older
- Quadrivalent adjuvant Recommended for people 65 and older and designed to stimulate an especially strong immune response. (Adjuvant means a substance is added to the vaccine to make it more effective so less vaccine is needed.)
- Quadrivalent high-dose Recommended for people 65 and older and designed to stimulate an enhanced immune response
- Live attenuated influenza vaccine A nasal mist vaccine recommended for ages 2 through 49 (but because it’s made from a live virus, it isn’t safe for people who are pregnant or have a compromised immune system)
2. Even healthy people should get a flu shot.
Although it’s more a risk for certain people, including newborns, people 65 and older, and those with a weakened immune system, anyone can have complications from the flu, or even die from it. No matter how young and healthy you are, the best way to prevent a serious outcome from having the flu is to get vaccinated. And you won’t be protecting only yourself — by being vaccinated, you help protect people who can’t safely get a flu shot.
3. Vaccination is not a guarantee you won’t get sick, but if you do, it still has benefits.
“Even if the flu vaccine isn’t perfectly matched with the dominant strain that’s circulating, that’s no reason to not get vaccinated,” says Dr. Schaffner.
Why? According to the CDC, even if you come down with the flu after you get a flu shot, it’s likely your symptoms won’t be as severe as if you weren’t vaccinated. You’ll probably get better faster too. And that’s even if you happen to be infected with a strain of the flu that isn’t in the vaccine.
4. You won’t be immediately protected from the flu after you get vaccinated.
It takes two weeks for your body to build immunity against the influenza virus. That means it’s possible to come down with the flu during the window of time between getting the shot and when immunity fully takes hold. That’s why experts recommend getting vaccinated in the fall, before the virus starts to circulate in earnest. By the time it does, if you’re vaccinated, your immune system will be primed to protect you.
5. You need a flu shot every year.
This is for two reasons, according to Andrew Pekosz, PhD, professor of molecular microbiology and immunology at the Johns Hopkins University Bloomberg School of Public Health in Baltimore.
“This first is, the flu vaccine is updated every year based on changes in the viruses that are circulating. So, to get the maximum protection against what we think will be the dominant viruses, you need to get your vaccine every year,” he explains. “The second is, the flu vaccine response does wane over time. So, you really need an extra dose every year to give you maximum protection from severe infection.”
6 FAQs About the Flu Shot
Who Should and Shouldn’t Get a Flu Shot?
Which Vaccination Is Best for Me?
Different vaccines are recommended for different age groups, for pregnant people, or for those who are immunocompromised or have certain health conditions.
For example, according Pekosz, “the flu mist is a good option for children, but isn’t used frequently in other age groups.” Also, this June, the CDC recommended everyone 65 and older get a high-dose or adjuvanted flu vaccine.
Work with your doctor to determine which vaccine is the right match for you, how to access it, and which vaccine to get if the you can’t.
At the end of the day, the goal is to get as many people vaccinated as possible. “We want you to protect yourself, your family, and your community,” says Schaffner. “So please — get vaccinated.”