Understanding the flu vaccine

Get the key facts regarding influenza and how the vaccine can prevent it from bugging you.

 
Why should people get vaccinated against the flu?

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. The Centers for Disease Control and Prevention (CDC) estimates that flu-related hospitalizations since 2010 ranged from 140,000 to 710,000, while flu-related deaths are estimated to have ranged from 12,000 to 56,000. During flu season, flu viruses circulate at higher levels in the U.S. population. (“Flu season” in the United States can begin as early as October and last as late as May.)


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.


Who should get vaccinated this season?

Everyone six months of age and older should get a flu vaccine every season. This recommendation has been in place since 2010. Vaccination to prevent influenza is particularly important for people who are at high risk of serious complications from influenza.


Who should not be vaccinated this season?

CDC recommends use of the flu shot (inactivated influenza vaccine or IIV) and the recombinant influenza vaccine (RIV).

The nasal spray flu vaccine (live attenuated influenza vaccine or LAIV) should not be used during 2016-2017. Different flu vaccines are approved for use in different groups of people. Factors that can determine a person’s suitability for vaccination, or vaccination with a particular vaccine, include a person’s age, health (current and past) and any allergies to flu vaccine or its components.


Talk to your primary care physician if you have concerns about getting a flu shot. Generally, those who meet any of the below criteria should not get the flu vaccine:  

  • Children less than six months of age
  • People who are experiencing a moderate to severe illness with a fever
  • People with life-threatening allergies to any ingredient in the flu vaccine (such as gelatin or antibiotics)*
  • People who previously developed the rare neurological disorder Guillain-Barré syndrome after receiving the seasonal flu vaccine

  *People diagnosed with an egg allergy can request an egg-free vaccination


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.

Children who need two doses of vaccine to be protected should start the vaccination process sooner, because the two doses must be given at least four weeks apart.


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 six months and older should get vaccinated annually.


Does the 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. Such protection is possible because antibodies made in response to the vaccine can provide some protection (called cross-protection) against different but related influenza viruses.


How effective is the flu vaccine?

Influenza vaccine effectiveness (VE) can vary from year to year and among different age and risk groups. For more information, visit the CDC's website regarding vaccine effectiveness or specifics about the 2017 - 2018 flu season.


What are the benefits of the flu vaccination?

  • Flu vaccination can keep you from getting sick with flu.

  • Flu vaccination can reduce the risk of flu-associated hospitalization, including among children and older adults.
    • Vaccine effectiveness for the prevention of flu-associated hospitalizations was similar to vaccine effectiveness against flu illness resulting in doctor’s visits in a comparative study published in 2016.

  • Flu vaccination is an important preventive tool for people with chronic health conditions.
    • Flu vaccination has been associated with lower rates of some cardiac (heart) events among people with heart disease, especially among those who experienced a cardiac event in the past year.
    • Flu vaccination also has been associated with reduced hospitalizations among people with diabetes (79%) and chronic lung disease (52%).

  • Flu vaccination helps protect women during and after pregnancy. Getting vaccinated against the flu can also protect a baby from flu after birth. (A mother can pass antibodies onto the developing baby during pregnancy.)
    • A study that looked at flu vaccine effectiveness in pregnant women found that vaccination reduced the risk of flu-associated acute respiratory infection (ARI) by about one half.
    • There are studies that show that vaccination of pregnant women can reduce their baby’s risk of flu illness by up to half. This protective benefit was observed for up to four months after birth.

  • Flu vaccination may make your flu illness milder if you do get sick.

  • Getting vaccinated also protects people around you, including those who are more vulnerable to serious flu illness, like babies and young children, older people, and people with certain chronic health conditions.


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