Flu Vaccine - When it Misses the Mark

Sunday March 8 2015

Flu Vaccine - When it Misses the Mark

Tara Loseth, R.Ph. March 2015

 Every year, scientists develop a vaccine to protect us against the current strains of flu.  What do we do when that vaccine does not match the current flu virus, and is less effective or ineffective?

 The flu vaccine introduces our body to several strains of influenza virus, allowing us to develop an immunity to these viruses.  This year, there is a strain of flu that does not match the ones in the vaccine.  This brings up several questions:   Why does the flu vaccine change every year?  Why is it less effective this year?  Is it still worth it to get the flu vaccine?  How else can I protect myself from the flu, and what do I do if I get the flu?

Why does the flu vaccine change every year?

Mutating Strains:  The first reason is that Influenza viruses are constantly mutating.  It takes time to develop a vaccine, and within that time, the flu is still being passed around from person to person and undergoing small changes.  Sometimes the change is very slight, and the flu vaccine works well.  Sometimes the change is great enough that, by the time the vaccine is distributed, it is less effective.

Different Strains:  The second reason is that there are several types of flu virus, which come and go in different years.  Scientists make the vaccine based on the strains they expect in the coming flu season.  Sometimes an unexpected flu strain, which we didn’t see in last year’s flu season, will pop up in the next season.  In this case, the flu vaccine will be less effective or ineffective.


Why is it less effective this year?

Just as in any other year, scientists base the vaccine on the strains of flu that are most common at the time, and those are expected to make a come-back in the coming season.  Unfortunately, no one can control when and how a flu virus will mutate.  And it is nearly impossible to detect a come-back of a less common strain in time to develop a vaccine for it. 

Three kinds of flu viruses commonly circulate among people today: influenza A (H1N1) viruses, influenza A (H3N2) viruses, and influenza B viruses.This year’s flu vaccine was designed to protect against the following types of virus:  an A/California/7/2009 (H1N1)pdm09-like virus, an A/Texas/50/2012 (H3N2)-like virus, and a B/Massachusetts/2/2012-like virus.  Most of the circulating H3N2 this year is different from the vaccine virus. This is probably responsible for reduced vaccine effectiveness against those viruses this season.


Is it still worth it to get the flu vaccine this year?

Possibly.  Even when the vaccine is not a match for the common circulating strain, it may still confer some benefit.  This is hard to measure in population studies, because it depends on many factors; how far off the vaccine is from the circulating strain, the study design, the population being studied and, potentially, which vaccine was used.  The Centre for Disease Control and Prevention states that “while determining how well a flu vaccine works is challenging, in general, recent studies have supported the conclusion that flu vaccination benefits public health, especially when the flu vaccine is well matched to circulating flu viruses.”


How else can I protect myself from getting the flu?

Other than the flu vaccine, the two most effective ways to avoid the flu are to wash your hands often and to avoid contact with those who have the flu.  For more information, see our article Flu Season - Stopping the Spread or visit Healthlink BC


What do I do if I get the flu?

Get plenty of rest and stay hydrated.  For a stuffy nose, a humidifier or saline nasal spray may help.  Gargle warm salt water for a sore throat.  For over-the-counter medications to help with congestion, cough or fever, talk to your local pharmacist.  Consult your health care provider early if you have a condition that puts you at higher risk of complications.  You should also call your health care provider if you experience: shortness of breath or difficulty breathing, chest pain, or signs of dehydration (such as dizziness when standing or low urine output).  For more information, visit Healthlink BC.

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