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Flu Season Is Here

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Yellow sign that says "FLU SEASON AHEAD" with red and orange trees during autumn in the background

Influenza is a serious disease that can lead to hospitalization and sometimes even death. Every flu season is different, and influenza infection can affect people differently, but millions of people get the flu every year, hundreds of thousands of people are hospitalized and thousands or tens of thousands of people die from flu-related causes every year. Even healthy people can get very sick from the flu and spread it to others. An annual seasonal flu vaccine is the best way to reduce your risk of getting sick with seasonal flu and spreading it to others. When more people get vaccinated against the flu, less flu can spread through that community.

How do flu vaccines work?

Flu vaccines cause antibodies to develop in the body about two weeks after vaccination. These antibodies provide protection against infection with the viruses that are in the vaccine.

The seasonal flu vaccine protects against the influenza viruses that research indicates will be most common during the upcoming season. Traditional flu vaccines, called “trivalent” vaccines, are made to protect against three flu viruses; an influenza A (H1N1) virus, an influenza A (H3N2) virus, and an influenza B virus. There are also flu vaccines made to protect against four flu viruses called “quadrivalent” vaccines. These vaccines protect against the same viruses as the trivalent vaccine and an additional B virus.

What kinds of flu vaccines are available?

Both trivalent and quadrivalent flu vaccines will be available.

Trivalent flu vaccines include:

  • Standard-dose trivalent shots (IIV3) that are manufactured using virus grown in eggs. One trivalent vaccine formulation can be given with a jet injector, for persons aged 18 through 64 years.
  • A high-dose trivalent shot, approved for people 65 and older.
  • A recombinant trivalent shot that is egg-free, approved for people 18 years and older.
  • A trivalent flu shot made with adjuvant (an ingredient of a vaccine that helps create a stronger immune response in the patient’s body), approved for people 65 years of age and older.

Quadrivalent flu vaccines include:

  • Quadrivalent flu shots approved for use in different age groups.
  • An intradermal quadrivalent flu shot, which is injected into the skin instead of the muscle and uses a much smaller needle than the regular flu shot. It is approved for people 18 through 64 years of age.
  • A quadrivalent flu shot containing virus grown in cell culture, which is approved for people 4 years of age and older.  

Are any of the available flu vaccines recommended over others?

For the 2018-2019 flu season, ACIP recommends annual influenza vaccination for everyone 6 months and older with any licensed, age-appropriate flu vaccine (IIV, RIV4, or LAIV4) with no preference expressed for any one vaccine over another.

Who should get vaccinated?

Everyone 6 months of age and older should get a flu vaccine every season. This recommendation has been in place since February 24, 2010 when CDC’s Advisory Committee on Immunization Practices (ACIP) voted for “universal” flu vaccination in the United States to expand protection against the flu to more people.

When should I get vaccinated?

You should get a flu vaccine before flu begins spreading in your community. It takes about two weeks after vaccination for antibodies to develop in the body that protect against flu, so make plans to get vaccinated early in fall, before flu season begins. CDC recommends that people get a flu vaccine by the end of October, if possible. Getting vaccinated later, however, can still be beneficial and vaccination should continue to be offered throughout the flu season, even into January or later.

Where can I get a flu vaccine?

Flu vaccines are offered in many locations, including doctor’s offices, clinics, health departments, pharmacies and college health centers, as well as by many employers, and even in some schools.

Even if you don’t have a regular doctor or nurse, you can get a flu vaccine somewhere else, like a health department, pharmacy, urgent care clinic, and often your school, college health center, or workplace.

The following Vaccine Locator is a useful tool for finding vaccine in your area.

Why do I need a flu vaccine every year?

A flu vaccine is needed every season for two reasons. First, the body’s immune response from vaccination declines over time, so an annual vaccine is needed for optimal protection. Second, because flu viruses are constantly changing, the formulation of the flu vaccine is reviewed each year and sometimes updated to keep up with changing flu viruses. For the best protection, everyone 6 months and older should get vaccinated annually.

Does flu vaccine work right away?

No. It takes about two weeks after vaccination for antibodies to develop in the body and provide protection against influenza virus infection. That’s why it’s better to get vaccinated early in the fall, before the flu season really gets under way.

Can I get seasonal flu even though I got a flu vaccine this year?

Yes. There is still a possibility you could get the flu even if you got vaccinated. The ability of flu vaccine to protect a person depends on various factors, including the age and health status of the person being vaccinated, and also the similarity or “match” between the viruses used to make the vaccine and those circulating in the community. If the viruses in the vaccine and the influenza viruses circulating in the community are closely matched, vaccine effectiveness is higher. If they are not closely matched, vaccine effectiveness can be reduced. However, it’s important to remember that even when the viruses are not closely matched, the vaccine can still protect many people and prevent flu-related complications. 

Vaccine Effectiveness

Influenza vaccine effectiveness can vary from year to year and among different age and risk groups. While it can vary, recent studies show vaccine reduces the risk of flu illness by about 40% to 60% among the overall population during seasons when most circulating flu viruses are like the vaccine viruses. 

For more information, visit the Centers for Disease Control web site.