Last year’s influenza season was not one that experts at the Advisory Committee on Immunization Practices (ACIP) at the Centers for Disease Control and Prevention (CDC) will remember as successful. Influenza A (H3N2) predominated for most of the year, with a spike in influenza B occurring late in the season. 

A moderately severe season overall was especially severe for those aged 65 and older. The problem was that the vaccine against the predominant strains of influenza A was less effective due to antigenic drift, which occurs when small changes in the flu virus over time make the vaccine less effective because the body does not recognize the changed virus as foreign.1

“Every year infectious disease scientists collect data from around the world and try to predict what strains of flu will predominate. It is an imperfect science. When the vaccine does not do well, the press raises concerns. That makes it more important that primary care providers spend time explaining to their patients what went wrong and why it will probably be better this year,” says Susan Coffin, MD, infectious disease specialist at the Children’s Hospital of Philadelphia and assistant professor of pediatrics at the Perelman School of Medicine at the University of Pennsylvania.


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What Went Wrong

In the 2013-2014 season, the strains of flu virus covered by the vaccine were well matched to the viruses that circulated  during the flu season. However, that was not the case in 2014-2015.1 More than 80% of the influenza A (H3N2) strains tested in 2014-2015 showed antigenic drift.2 Statistics from the CDC show that the vaccine was only 19% effective in preventing medical visits for flu across all age groups.1

“Influenza is an epidemic that occurs every year. In a good year, the vaccine may be 50% to 60% effective, but despite the best guesses of the experts, nature is unpredictable. If you were in part of the country where the B viruses predominated, you were better protected. If A predominated, you were not,” says Pedro A. Piedra, MD, professor of virology and microbiology at Baylor College of Medicine in Houston, Texas.

For the 2014-2015 season, the ACIP had recommended using the live attenuated influenza vaccine (LAIV) compared with the inactivated influenza vaccine (IIV) for healthy children aged 2 through 8 years.3 “Last year the ACIP stressed live over killed vaccine, but the statistics showed that there was no difference—and possibly a slight advantage—to the killed vaccine,” says Dr Coffin.

Changes for 2015-2016

New vaccine options will be available for clinicians during the 2015-2016 season. The trivalent vaccine will cover the influenza A strains California and Switzerland, as well as an influenza B strain called Phuket. An influenza B strain called Brisbane will be added to the quadrivalent vaccine.1

“The FDA and the World Health Organization have made two changes: the A Switzerland and the B Phuket are new, and the A California and B Brisbane will remain the same. Hopefully last year’s poor showing will not decrease the percentage of Americans who get vaccinated. The CDC estimates that about 45% of Americans get the vaccine. For Americans older than 65, the percentage is about 75%,” says Dr. Piedra.

There is no significant difference in using LAIV over IIV in healthy children in the guideline update, but there is a new recommendation for the number of doses needed by children aged 6 months through 8 years. A child who has received two or more doses of flu vaccine in the past will only need one dose this year. If the child has never received two doses, the child should receive two doses given at least four weeks apart.3 “The key change is from two doses in the last year to two doses ever,” explains Dr Coffin.

Expert Tips for Flu Season

Both Dr Coffin and Dr Piedra agree that the quadrivalent vaccine is better than the trivalent vaccine if a patient is provided with a choice, but they also agree that people  should not skip getting a flu shot if the quadrivalent vaccine is unavailable.  “More is better but not if you have to wait for it. Go with what is available,” says Dr Coffin.

One bright spot from the 2014-2015 season is that almost all strains of flu tested are still sensitive to the common antiviral agents.1 “Once someone has the flu, antivirals should be started as soon as possible for anyone who is at higher risk for complications. That includes the very young and the very old, anyone with a comorbid condition, and anyone who is in the hospital,” says Dr Piedra.

“The ideal time to give the vaccine is in October or November, but September is also good and so is later in the year. Even if there is an outbreak of flu, giving the vaccine can help. In most cases, protection will kick in several weeks before the virus peters out,” advises Dr Coffin.

And of course, there are these tried-and-true CDC preventive strategies4:

  • Avoid contact with sick people.
  • Stay home with the flu for last least 24 hours after your fever breaks.
  • Use tissues to cover your nose and mouth while sneezing or coughing. Throw away the tissue immediately after using it.
  • Wash your hands frequently with soap and water or an alcohol-based hand sanitizer.
  • Do not touch your hands to your face.
  • Use a disinfectant to clean surfaces and objects at home, work, and school.

“The key point is that the effectiveness of flu vaccine is unpredictable from year to year, but it is always the best protection against the flu. Vaccination is the way to go,” says Dr Piedra.

Medically reviewed by: Pat F. Bass III, MD, MS, MPH

References

1. Centers for Disease Control and Prevention, Influenza Activity–United States, 2014-15 Season and Composition of the 2015-16 Influenza Vaccine. http://www.cdc.gov/mmwr/preview/mmwrhtml/mm6421a5.htm. Accessed September 9, 2015. 

2. Centers for Disease Control and Prevention for the 2014-2015. CDC presents updated estimates of flu vaccine effectiveness for the 2014-2015 season.  http://www.cdc.gov/flu/news/updated-vaccine-effectiveness-2014-15.htm. Accessed September 9, 2015. 

3. Prevention and Control of Seasonal Influenza with Vaccines: Recommendations of the Advisory Committee on Immunization Practices (ACIP) — United States, 2014–15 Influenza Season.  MMWR. 2014;63(32):691-697.

4. Centers for Disease Control and Prevention. “Take 3” actions to fight the flu. http://www.cdc.gov/flu/protect/preventing.htm. Accessed September 9, 2015.