Research

How Effective Is the Flu Vaccine in 2021-2022?

Alyssa Corso22 Sep 2021

Recent studies show that flu vaccination reduces the risk of flu illness by between 40% and 60% among the overall population during seasons when most circulating flu viruses are well-matched to those used to make flu vaccines. Flu vaccine effectiveness usually varies from season to season. There are at least two factors that play an essential role in determining the likelihood that vaccination will protect a person from flu illness: 

1) Characteristics of the person being vaccinated (such as their age and health).

2) How well the vaccines "match" the flu viruses spreading in the community.

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Flu Vaccine Effectiveness

Since flu vaccine effectiveness varies, researchers and scientists will begin to estimate the effectiveness of the 2020–2021 flu vaccine in the coming months.

However, it's possible to evaluate flu vaccine effectiveness based on data from the previous seasons. Below we analyze flu vaccine effectiveness. 

Flu Vaccine Effectiveness By Year

Below we outline the effectiveness of the flu vaccine by year.

YearEffectiveness
200410 percent
200521 percent
200652 percent
200737 percent
200841 percent
200956 percent
201060 percent
201147 percent
201249 percent
201352 percent
201419 percent
201548 percent
201640 percent
201738 percent
201829 percent
201939 percent

Flu Vaccine Effectiveness By Age Group

There can be a range of variance in flu vaccine effectiveness when it comes to specific age groups. The CDC tracks this data as well as data on the flu's overall effectiveness.

Below we outline flu vaccine effectiveness estimates for all vaccine types across different age groups from the past five flu seasons.

Flu seasonAll ages6 months to 8 years9 to 17 years18 to 49 years50 to 64 years65 years and older
2019–202039 percent34 percent40 percent34 percent40 percent39 percent
2018–201929 percent48 percent7 percent25 percent14 percent12 percent
2017–201838 percent68 percent32 percent33 percent30 percent17 percent
2016–201740 percent57 percent36 percent19 percent40 percent20 percent
2015–201648 percent51 percent59 percent52 percent26 percent42 percent

How Long the Flu Vaccine is Effective For

A flu vaccine should protect you through the current flu season. You'll need to receive another flu vaccine for the next flu season. There are several reasons why a flu vaccine is only effective for one flu season.

  • Influenza viruses change constantly. Because of this, the strains included in this year's flu vaccine may not be the most common strains during next year's flu season.
  • The level of protection (immunity) generated by the flu vaccine wanes over time.

For example, a 2019 study found that, across seven flu seasons, every additional 28 days after vaccination was associated with a 16 percent increase in the likelihood of testing positive for flu.

Factors that Influence Flu Vaccine Effectiveness

While flu vaccine effectiveness can vary throughout the different seasons, certain factors influence why this happens.

The Flu Strains Used in the Vaccine

Because influenza strains are always changing, the strains that were common during last year's flu season may not be as prevalent for the current flu season. Each year, scientists select the strains to include in the flu vaccine for countries in the northern hemisphere, including the United States. 

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Based on current surveillance data prediction, vaccine strains that are chosen may be the most common strains for the upcoming flu season. However, it is possible that the selected strains for the vaccine don't match with the strains that end up being most prevalent during a flu season. When this occurs, vaccine effectiveness can be low. If the strains selected are a good match to the one used in the vaccine, vaccine effectiveness is higher.

Influenza Virus Subtype

Flu vaccines are designed to protect against two types of influenza virus: influenza A and influenza B. 

Influenza A viruses are very diverse and are further divided into different subtypes. Two prevalent subtypes are H1N1 and H3N2.

Typically, flu vaccines give better protection for influenza B and H1N1 strains. However, they provide less protection against H3N2 strains. This is due to the various genetic changes that can commonly happen in H3N2 viruses.

A 2016 review looked at 142 studies on flu vaccine effectiveness by flu type. It found that:

  • Vaccine effectiveness against H3N2 strains was only 33 percent.
  • Meanwhile, vaccine effectiveness was 54 percent and 61 percent against influenza B and H1N1 strains, respectively.
  • When H3N2 vaccine strains were a good match, vaccine effectiveness was still only 33 percent. When vaccines weren't a good match, effectiveness dropped to 23 percent.

Therefore, if H3N2 strains are more common during a flu season than other types of influenza, the vaccine's effectiveness can be lower.

Personal Factors 

Age and overall health can also impact vaccine effectiveness. For instance, older adults tend to have a weaker response to influenza virus vaccination. High-dose flu vaccines are available for adults aged 65 and older.

Large-scale studies of vaccine effectiveness in this population have found that the high-dose vaccine is slightly more effective than standard-dose vaccines.

Who Should Get the Flu Vaccine

The current recommendation for the 2020–2021 flu season is that all individuals aged six months and older receive a flu vaccine. If you are at an increased risk of severe illness from the flu, it'svaccine's essential to get the flu vaccine. This includes:

  • Adults aged 65 and older
  • Children younger than five years old
  • Pregnant women
  • People with chronic health conditions, such as asthma, heart disease, and diabetes
  • Those with a weakened immune system

Available Flu Vaccines in 2021-2022

Vaccine nameAge rangeHow it's givenPotential allergens
Afluria Quadrivalent6 months
or older
IntramuscularEgg protein, neomycin, polymyxin
Fluad Quadrivalent65 years
or older
IntramuscularEgg protein, kanamycin, neomycin, polysorbate 80
Fluarix Quadrivalent6 months
or older
IntramuscularEgg protein, gentamicin, polysorbate 80
Flublok Quadrivalent18 years
or older
IntramuscularPolysorbate 20
Flucelvax Quadrivalent2 years
or older
IntramuscularPolysorbate 80
FluLaval Quadrivalent6 months
or older
IntramuscularEgg protein, polysorbate 80
FluMist Quadrivalent2-49 yearsNasal sprayEgg protein, gentamicin, pork gelatin
Fluzone High-Dose Quadrivalent65 years
or older
IntramuscularEgg protein
Fluzone Quadrivalent6 months
or older
IntramuscularEgg protein

It's important to note that pharmacies and healthcare providers may not carry all types of flu vaccines. If you are interested in or know you need a certain flu vaccine, you may want to call beforehand and see if your preferred vaccine is available.

Which Flu Vaccine Is Most Effective in 2021-2022

Regardless of what vaccine you choose, you're being protected against the same flu strains. 

Flu vaccines are typically between 40% and 60% effective from year to year. But when it comes to picking the right flu vaccine for you, you have to take other factors into account.

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Most Effective Flu Vaccine for Individuals Over 65

People over the age of 65 can have a harder time responding to illnesses and vaccines. To help provide even greater protection against the flu, there are a few recommended options for older adults this year:

  • Fluzone High-Dose Quadrivalent — also known as the "high-dose flu shot"
  • Fluad Quadrivalent
  • Flublok Quadrivalent

You should still get vaccinated with another flu vaccine that's FDA-approved for your age range, even if the quadrivalent vaccines aren't available. All flu vaccines are effective against the flu. It's better to be vaccinated than to try to wait for a particular flu vaccine to become available.

Benefits of Getting a Flu Vaccine

Each year, there are plenty of benefits to getting the flu vaccine.

Helps Protect You from the Flu

Flu vaccination prevents millions of illnesses and flu-related doctor's visits each year. For example, during 2019-2020, flu vaccination prevented an estimated 7.5 million influenza illnesses, 3.7 million influenza-associated medical visits, 105,000 influenza-associated hospitalizations, and 6,300 influenza-associated deaths.

During seasons when flu vaccine viruses are similar to circulating flu viruses, the flu vaccine has been shown to reduce the risk of going to the doctor with flu by 40 percent to 60 percent.

Reduces Severity of the Flu

Even if you contract the flu after getting your vaccine, it will likely reduce the severity of your symptoms.

A 2021 study showed that among adults, flu vaccination was associated with a 26% lower risk of ICU admission and a 31% lower risk of death from flu compared to those who were unvaccinated. A 2018 study showed that vaccinated patients were 59 percent less likely to be admitted to the ICU among adults hospitalized with flu than those who had not been vaccinated. Among adults in the ICU with flu, vaccinated patients, on average, spent four fewer days in the hospital than those who were not vaccinated.

Reduces Hospitalization

Along with reducing the severity of symptoms, flu vaccination prevents tens of thousands of hospitalizations each year. For example, during 2019-2020, flu vaccination prevented an estimated 105,000 flu-related hospitalizations.

A 2014 study showed that flu vaccination reduced children's risk of flu-related pediatric intensive care unit (PICU) admission by 74 percent during flu seasons from 2010-2012. A 2017 study found that during 2009-2016, flu vaccines reduced the risk of flu-associated hospitalization among older adults by about 40 percent on average. A 2018 study showed that from 2012 to 2015, flu vaccination among adults reduced the risk of being admitted to an intensive care unit (ICU) with flu by 82 percent.

A 2018 study showed that getting a flu shot reduced a pregnant person's risk of being hospitalized with flu by an average of 40 percent from 2010-2016. 

Helps to Protect High-Risk Individuals

Flu vaccination has been associated with lower rates of cardiac events among people with heart disease, especially those who have had a cardiac event in the past year. Flu vaccination can reduce the risk of a flu-related worsening of chronic lung disease (for example, chronic obstructive pulmonary disease (COP) requiring hospitalization. Among people with diabetes and chronic lung disease, flu vaccination also has been shown in separate studies has also been associated with reduced hospitalizations from a worsening of their chronic condition. Vaccination reduces the risk of flu-associated acute respiratory infection in pregnant people by about one-half.

Several studies have shown that in addition to helping to protect pregnant people from flu, a flu vaccine given during pregnancy helps protect the baby from flu for several months after birth when they are too young to be vaccinated. Along with this, a 2017 study was the first of its kind to show that flu vaccination can significantly reduce a child’s risk of dying from flu.

The Bottom Line

The flu vaccine can help protect you and protect others. While effectiveness ranges each season depending on different factors, some studies prove its'child's benefits.