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When is Flu Season Really?

Updated: Oct 6, 2023

Every year, chain pharmacies begin marketing flu shots earlier, with some even offering them as early as July. But when does flu season really begin? And when is the right time to get your flu shot to stay healthy through all of fall and winter? With so much conversation surrounding vaccines in 2022, it can be difficult to parse through the onslaught of information, so we broke it down with simplified answers to the most common questions about flu season and flu shot timing.

When is flu season in the US?

In the United States, flu season is in the fall and winter. However, influenza viruses are still present and circulating in year-round. Flu cases generally peak between December and February, and sometimes lingers as late as May. The CDC collects and analyzes influenza data year-round to track flu activity and makes weekly updates to their surveillance report, FluView.1

Why is flu season always in the fall and winter?

To understand the timing of flu season, one must first understand how the flu virus is passed from person to person. The flu is a respiratory illness that is spread primarily through droplets made when an infected person talks, sneezes, and coughs. When these droplets containing the virus land in the mouths or noses of other people or make their way into another individual’s mouth or nose via a contaminated surface, the infection is spread.

A common misconception is that the flu is caused by cold temperatures, but this is not the case. Cooler temperatures in the fall and winter means spending more time indoors, which leads to closer proximity to others and an increased likelihood of droplets spreading.

Some studies suggest that there may be other contributing factors that increase the spread of flu during cold months. For example, lack of sunlight in the fall and winter leads to low levels of vitamin D and melatonin, which may weaken our immune systems. Another theory is that the influenza virus prefers colder, drier climates and, therefore, may be able to infect more people.2

Do other viruses circulate during flu season?

Yes! Any viruses that are present year-round and passed along via droplets or airborne transmission may also experience increased activity when more people are staying inside. This includes the common cold, COVID-19, and respiratory syncytial virus (RSV). Therefore, especially in the fall and winter, it is important to wash your hands regularly, avoid being in close contact with others who are sick, regularly disinfect commonly touched surfaces, and practice good health habits to keep your immune system strong.

When is the best time to get a flu shot?

The CDC states, “For most persons who need only one dose of influenza vaccine for the season, vaccination should ideally be offered during September or October. However, vaccination should continue throughout the season as long as influenza viruses are circulating.” For most populations, getting vaccinated in July or August could lead to waning efficacy near the tail end of flu season, meaning those who get vaccinated to soon may be more likely to get sick in March, April, or May. However, there are some exceptions to the rule.

  • Children 6 months through 8 years who require 2 doses should receive the first dose as soon as the vaccine is available.

  • Vaccination during July and August can be considered for children of any age who require only one dose.

  • Vaccination in July and August can be considered for pregnant persons who are in the third trimester during those months.

Don’t wait too long to get your flu shot either—it takes about two weeks after vaccination for antibodies to develop in the body to fully protect against the flu.3

Why do I need a flu shot every year?

There are two reasons why the CDC recommends that individuals get a flu shot annually. First, a person’s immunity from the flu vaccine decreases over time. The second reason is because influenza viruses are always changing, and each year a new vaccine is developed to protect against which flu viruses the data predicts will be the most prevalent during the upcoming flu season. The most common flu vaccine is called the quadrivalent vaccine and protects against the top four flu virus strains predicted for that year.4

What are the different types of flu shots?

When you go to get your flu shot, you may have options. These are the different types of flu vaccines:

  • Quadrivalent Flu Vaccine protects against four different flu viruses.

  • High-Dose Flu Vaccine contains four times the amount of antigen as a regular flu shot to create a stronger immune response. This option is only approved for people 65 years and older.

  • Adjuvanted Flu Vaccine is formulated with an ingredient called an adjuvant that helps create a stronger immune response. This option is only approved for people 65 years and older.

  • Nasal Spray Flu Vaccine, also known is FluMist, is administered as a nasal spray and is approved for individuals aged 2 through 49 years. This vaccine is not recommended for pregnant people, immunocompromised people, or people with certain medical conditions.

  • Cell-Based Flu Vaccine is completely egg-free and is approved for people 6 moths and older.5

Are any of the available flu vaccines recommended over others?

The CDC says that there is no preferential flu vaccine recommendation for people younger than 65 years. If you are over 65 years, the high-dose or adjuvanted flu vaccine is recommended. If the preferentially recommended flu vaccine is not available at the time of administration, individuals should get any other age-appropriate flu vaccine instead.4

Who should be vaccinated?

Everyone 6 months and older in the US should the influenza vaccine, especially people who are at higher risk of developing flu-related complications. Exceptions to this rule are rare. For more information about who should talk to their doctor before getting the flu vaccine can be found on the CDC website.

How well does the flu vaccine work?

Vaccine effectiveness can vary from season to season. During years where the most common flu virus predictions are more accurate, the vaccine will be more effective.

According to the CDC:

  • Flu vaccine prevents millions of illnesses and flu-related doctor’s visits each year. For example, during 2019-2020, the last flu season prior to the COVID-19 pandemic, 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, flu vaccine has been shown to reduce the risk of having to go to the doctor with flu by 40% to 60%.

  • A 2021 study showed that among adults hospitalized with flu, vaccinated patients had a 26% lower risk of intensive care unit (ICU) admission and a 31% lower risk of death from flu compared with those who were unvaccinated.

  • A 2022 study showed that flu vaccination reduced children’s risk of severe life-threatening influenza by 75%.

It is possible that a person who is vaccinated may still become sick with the flu, particularly if they contract the flu within two weeks after vaccination (before antibodies are created) or are exposed to a flu virus that is not included in the seasonal vaccine. Vaccine effectiveness is not 100 percent but is still the best way to protect against the flu and mitigate the severity of infection.4

Can I get a COVID-19 vaccine at the same time as my flu shot?

Researchers have confirmed that is safe to receive the flu and COVID-19 vaccines at the same time. But remember, don’t delay vaccination just to get them both during the same visit!

THE KEY TAKEAWAY: Nearly everyone ages 6 months and older should get their flu vaccine in September or October to make sure they stay healthy all season long. For more information about flu shots and vaccine timing, talk to your pharmacist today.



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