How Effective Is the Flu Vaccine?

According to the CDC, the flu vaccine reduces the odds of getting the flu by 70% to 90%. 

You may wonder why there’s such a wide range.  And in fact, it’s even wider than it seems: that statistic only applies to healthy adults.  It turns out that the effectiveness of the flu vaccine depends on a number of different factors.  Here’s a rundown of what they are.

• Your Age

The flu vaccine doesn’t work equally well in all people.  It’s most effective in healthy adults.  In young children, the flu vaccine is a little less effective -- about 66% -- at preventing the flu.  It’s more effective as children get older. 

After middle age, your immunity naturally becomes weaker. The flu vaccine won’t work as well as it once did.  But since the flu virus is much more dangerous for older people, it’s crucial that they get the vaccine.  Even in cases where it doesn’t prevent the flu, it can still reduce the risk of serious side effects.  Studies show that in older people who do not live in a care facility, the flu vaccine can cut the risk of hospitalization (for flu and pneumonia) by 30% to 70%.  In people who do live in a nursing home or care facility, the flu vaccine is 50% to 60% effective in preventing hospitalization and 80% effective in preventing death from a flu complication.

There may also be slight differences depending on which vaccine you get.  Some research shows that the nasal flu vaccine may offer the best protection for children.  But it may also be less effective than the injected flu vaccine in the elderly.

• Your General Health

Vaccines work by spurring your immune system into action. In a sense, a vaccine “teaches” your body how to identify a virus and how to defend against it. Then, when you come into contact with the actual virus, your immune system quickly recognizes it and fights it off.

So the effectiveness of a vaccine depends on how vigorously your immune system responds to it.  If you have a weak immune system to begin with, a vaccine may just not work as well.  Many chronic illnesses can weaken your body’s defenses. The CDC estimates that the flu vaccine reduces the risk of hospitalization (for flu and pneumonia) by 30% to 70% in people with chronic illnesses.

• When You Get the Flu Vaccine

While the flu vaccine was once only be available between October and the end of November, experts stress that you can now get it into December and January.  Keep in mind that the flu season often doesn’t peak until February or later.

But the sooner you get it, the better.  Why? Simple: the further you get into the flu season, the higher your risk of getting flu.  Here’s something else to keep in mind: it can take two weeks for the flu vaccine to take effect.  So if you’re exposed to the flu within that two week period, you might still get sick.

• How Well the Vaccine Is Matched With the Dominant Flu Strains