Skip to content
My WebMD Sign In, Sign Up

Cold, Flu, & Cough Health Center

Font Size

Flu Shot Failure? Questions & Answers

The annual flu vaccine may not be as effective this year as in past years, the CDC has announced. Here's why.
By
WebMD Feature
Reviewed by Louise Chang, MD

The CDC reports this year's flu shot may not protect against a strain of influenza that's hitting the U.S.

Q. Does this mean the flu shot is useless?

Recommended Related to Cold & Flu

Novel H1N1 Flu (Swine Flu) and Feeding your Baby: What Parents Should Know

This document updates previously posted information for parents about infant feeding and novel H1N1 flu (swine flu).  It now more clearly addresses parents who are formula feeding as well as breastfeeding, suggests that parents sick with novel H1N1 flu (swine flu) find someone who is not sick to feed the baby, and provides more detailed strategies for breastfeeding mothers to maintain breastfeeding throughout the course of infection. This document is based on current knowledge of the novel...

Read the Novel H1N1 Flu (Swine Flu) and Feeding your Baby: What Parents Should Know article > >

Not at all. Although this year's flu vaccine doesn't match two of the three main types of flu strains now in circulation, people who did get a flu shot and catch the flu get a much milder disease. This can make a life-or-death difference to people who are at high risk of flu complications, such as pregnant women, young children, the elderly, and those with chronic medical conditions such as diabetes, asthma, and heart disease.

At the Feb. 27 meeting of the CDC's Advisory Committee on Immunization Practices, University of Virginia professor James C. Turner, MD, said a UVA study found this year's vaccine to be 41% protective against serious flu illness. A similar study in 2003 found that year's vaccine to be 69% protective. 

Turner, executive director for student health at UVA, said the school this year had a "robust" flu outbreak. Because UVA has a unique program that tracks students' flu vaccination status and uses rapid flu tests to detect flu outbreaks, CDC flu experts tell WebMD that this estimate is probably accurate, although the vaccine may be more or less protective in different regions of the country.

Q. Why was there a mismatch in this year's flu shot?

Flu vaccines contain a mixture of two influenza "A" virus strains -- this year they are types H3N2 and H1N1 -- and a "B" virus strain. These viruses mutate or "drift" a little each year, which is why the annual flu vaccine must be reformulated each year.

Most years, experts manage to match their flu vaccine selections in the spring to the strains that circulate later in the year throughout the U.S. and globally. In winter 2007, experts considered including a particular H3N2 strain of influenza A, but dropped the plan when they couldn't find samples that would grow properly in the manufacturing process.

Influenza A typically makes up about 85% of all flu cases. However, this year the particular H3N2 strain that was left out of the vaccine wound up being the dominant influenza A virus, which accounts for more than 60% of flu cases.

Q. Who determines which influenza strains go into each year's vaccine?

The CDC collaborates with the World Health Organization (WHO) and other groups to track the flu virus throughout the world. These organizations also monitor influenza activity and virus isolates throughout the world to monitor disease activity and forecast the appropriate components for each year's flu vaccine.

Because of this year's vaccine mismatch, a government scientific advisory board recommended for the first time this week a complete overhaul of the makeup of the flu vaccine for next year. This move would replace all three flu virus strains in this year's vaccine with three new strains for next year flu season.

Today on WebMD

hot toddy
15 tips to help you feel better.
man sneezing into elbow
Do echinacea and vitamin C really help a cold?
 
teen girl coughing
Get a good night’s rest with these remedies.
elder berry
Eat these to fight colds, flu, and more.
 
Natural Cold Flu Remedies Slideshow
Slideshow
blowing nose
VIDEO
 
Allergy And Sinus Symptom Evaluator
Health Check
Boy holding ear
Article
 
woman receiving vaccine shot
Article
Bacterial or Viral Infection
Video
 
How To Calm Your Cough
Quiz
Sore Throat
Slideshow
 

WebMD Special Sections