Questions About Flu Vaccine


Who should get vaccinated this season?

Everyone who is at least 6 months of age should get a flu vaccine this season. There are also people who are at high risk of developing serious complications. See these lists for more details:

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Is it too late to get a flu shot?

 If you haven't gotten your flu vaccine yet, there is still time to protect yourself and your family by getting vaccinated. Flu season may not peak in Oregon until February or March. It's also possible that we could continue to see flu in the United States until May.

Flu vaccines are offered in many doctors' offices, clinics, grocery stores, pharmacies, local health departments, and possibly even your child's school or your workplace. So even if you don't have a regular doctor, you can get a flu vaccine at many other locations.

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Why do I need a flu vaccine every year?

A flu vaccine is needed every year because flu viruses change. It’s not unusual for new flu viruses to appear each year. The flu vaccine is made each year to keep up with the flu viruses as they change.

Also, multiple studies conducted over different seasons have shown that the body’s immunity to influenza viruses (acquired either through natural infection or vaccination) declines over time. Getting vaccinated each year provides the best protection against influenza throughout flu season.

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Is the flu vaccine safe?

This season’s flu vaccine is expected to have a similar safety profile as past seasonal flu vaccines. Over the years, hundreds of millions of Americans have safely received seasonal flu vaccines. The most common side effects are soreness, redness, tenderness or swelling where the flu shot was given and nasal congestion after the flu vaccine nasal spray.

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How effective is the flu vaccine?

Influenza vaccine effectiveness can vary from year to year and among different age and risk groups. More information about vaccine effectiveness>>

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What are the potential side effects from the flu shot?

Most people will not experience side effects from influenza vaccine. If side effects occur, they will likely be mild. In adults, the main side effect is soreness, redness or swelling in the arm where the shot was given. A small fraction of children who get influenza vaccine may develop mild fever and/or muscle aches. These side effects usually begin soon after the shot and last 1-2 days.

As with any medicine, there is a very small chance that an unexpected or severe allergic reaction may occur, but serious problems from the flu vaccine are very rare. The risk from the vaccine is much smaller than the risk from the disease. However, if you have a severe (life-threatening) allergy to chicken eggs or to any other substance in the vaccine, you should not be vaccinated.

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Will I get the flu from the flu shot?

No. But there are several reasons why someone might get flu-like symptoms even after they have been vaccinated against the flu:

  • People may be exposed to an influenza virus shortly before getting vaccinated or during the two-week period that it takes the body to gain full protection after getting vaccinated. This exposure may result in a person becoming ill with flu before the vaccine begins to protect them.
  • People may become ill from other (non-flu) viruses that circulate during the flu season, which can also cause flu-like symptoms. These viruses may cause you to feel ill, but are less serious than influenza.
  • A person may be exposed to an influenza virus that is not included in the vaccine they received. There are many different influenza viruses, and the flu vaccine protects against the most common ones.
  • No medication is 100% effective. Unfortunately, some people, like those that have weakened immune systems, can remain unprotected from flu despite getting the vaccine. However, even among some people with weakened immune systems, the flu vaccine can often help prevent more severe illness from influenza and the benefits to them are even greater because of their increased risk for serious problems from the flu.

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Do I need to get vaccinated if I've already had the flu?

Circulating flu viruses tend to be slightly different from year to year. Unless you were tested for a specific flu virus, you cannot be sure what made you sick. Getting this year’s seasonal influenza vaccine will help protect you and others in case what you already had was not the flu. If you did have a type of flu, the seasonal flu vaccine will protect you against the other most common strains of flu.

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How are the viruses selected to make flu vaccine?

The influenza (flu) viruses selected to be in the vaccines are updated each year based on which influenza viruses are being found, how they are spreading, and how well the previous season's vaccine might protect against new ones. Currently, more than 100 national influenza centers in more than 100 countries conduct year-round surveillance for influenza viruses and disease activity. These laboratories then send influenza viruses for additional analyses to five Collaborating Centers for Reference and Research on Influenza, which are located in the following places:

  • Atlanta, Georgia, USA (Centers for Disease Control and Prevention, CDC);
  • London, United Kingdom (National Institute for Medical Research);
  • Melbourne, Australia (Victoria Infectious Diseases Reference Laboratory);
  • Tokyo, Japan (National Institute for Infectious Diseases); and
  • Beijing, China (National Institute for Viral Disease Control and Prevention).

Vaccine viruses are chosen to by the likelihood that the influenza vaccine will protect against those most likely to spread and cause illness during the upcoming flu season. The World Health Organization (WHO) recommends specific vaccine viruses for influenza vaccine production, but then individual countries make their own decisions for licensing of vaccines in their country. In the United States, the FDA determines what viruses will be used in U.S.-licensed vaccines.

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What flu viruses does the vaccine prevent against?

Flu vaccines are designed to protect against three influenza viruses that experts predict will be the most common during the upcoming season. Three kinds of influenza viruses commonly circulate among people today:  influenza A (H1N1) viruses, influenza A (H3N2) viruses and influenza B viruses. Each year, one flu virus of each kind is used to produce seasonal influenza vaccine.

The 2012-2013 influenza vaccine is made from the following three viruses:

  • An A/California/7/2009 (H1N1)-like virus
  • An A/Victoria/361/2011 (H3N2)-like virus
  • A B/Wisconsin/1/2010-like virus

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Should pregnant women get vaccinated for the flu?

Yes, it is very important for a pregnant woman to get an influenza vaccination. A pregnant woman who gets any type of flu is at risk for serious health complications, hospitalization and even death. Pregnant women infected with influenza virus are much more likely than other flu patients to require hospitalization.

Handwashing and avoiding people who are ill can help protect pregnant women from the flu, but vaccination is the single best way to protect against the flu.

Research also shows that more than 60% of pregnant women who got the influenza vaccine passed on the immunity to their infants, which is important because babies cannot be vaccinated against the flu until they are more than 6 months old. Getting the flu vaccine protects both the mother and the baby from the flu.

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Is there a special kind of vaccine that pregnant women should get?

There are two types of flu vaccine: 

  • The injectable “flu shot” that is given with a needle, usually in the arm. The flu shot is approved for use in pregnant women.
  • Nasal-spray flu vaccine (FluMist) — is a weakened live virus vaccine that is not routinely given to pregnant women.

Most types of injectable flu vaccine contain the preservative thimerosal, which contains a very small amount of mercury. There is no evidence that thimerosal is harmful to a pregnant woman or a fetus. However, because some women are concerned about exposure to preservatives during pregnancy, manufacturers are producing preservative-free seasonal flu vaccine.

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Why do kids need more vaccine?

According to the CDC, the first dose "primes" the immune system and the second dose provides immune protection. If your child needs 2 doses, begin the process early, so that children are protected before influenza starts circulating in your community. Be sure to follow up to get your child a second dose if he or she needs one. It usually takes about two weeks after the second dose for protection to begin.

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Can I get a thimerosal-free influenza vaccine?

Thimerosal is a mercury preservative in many forms of vaccine. Thimerosal is used in vaccines to prevent bacterial contamination. Although some people are concerned about health risks from thimerosal, it has never been shown to cause any health problems. A report by the Institute of Medicine of the National Academies of Science concluded that thimerosal in vaccines does not cause health problems, a conclusion also reached by researchers in other countries around the world. The American Academy of Pediatrics, the CDC and the Institute of Medicine have concluded, based on scientific data, that thimerosal-containing vaccines are safe. 

Some influenza vaccines are available in thimerosal-free formulations, including the nasal spray vaccine. However, the majority of influenza vaccines do contain small amounts of thimerosal as a preservative to prevent bacterial contamination.

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More Information

Influenza, vaccine safety, the 2012-2013 flu season (CDC) 

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