Ask Emily

27 10 2011

I got a flu vaccine one year and ended up getting the flu anyway. Doesn’t that mean the vaccine doesn’t work?

Influenza viruses are notorious for constantly changing. Making vaccines against them is also notoriously difficult because it requires several months of advance preparation before the viral doses can be ready.

If you’ve heard of “bird flu,” you may realize that flu viruses flourish pretty well in the bird-related environment, and vaccine developers grow their viruses within fertilized chicken eggs (that’s why you’ll be asked if you’re allergic to egg proteins). Every vaccine requires about three eggs to yield sufficient (killed) virus, which translates into millions of chicken eggs (i.e., making 300 million vaccine doses would require 900 million eggs).

It also translates into six months of lead time for producing the viruses required to make the vaccine. To find out more about the current year’s strain selection, visit the Centers for Disease Control and Prevention site, which offer comprehensive information about influenza vaccines.

That advanced lead time means a delay between growing the viral strains authorities have determined may be most prevalent in the upcoming flu season and the actual arrival of the current season’s viruses. Experts can keep an eye on how flu goes in the southern hemisphere’s winter and use that as a gauge for which strains may be most prominent during winter in the northern hemisphere, but there’s no real guarantee that the viral strains pinpointed as most likely for a given season will turn out to be an accurate prediction.

The global surveillance network consists of 130 centers in 101 countries monitoring which strains are most prevalent. These are the people who try to predict months ahead of time which patterns of infection will prevail in a given geographic area.

So, it’s possible to be vaccinated against the flu and still get the flu. Why? Because if you’re exposed to a circulating strain that’s not included in this year’s vaccination mix, then you’re not vaccinated against catching that particular form of the virus. The good news is, the predictions generally turn out to be pretty on target, preventing most people who receive a vaccine from developing influenza.

Keep in mind that even if the vaccine misses a circulating strain, if you choose not to be vaccinated, you can contract influenza more than once in a season if you’re exposed to two different circulating strains.

Final answer? Yes, you can receive a flu vaccine and still come down with the flu. But that doesn’t mean the vaccine didn’t work. It did work against the strain it targeted, and if it hadn’t, you might’ve had to go through that misery more than once. So, get the influenza vaccine as indicated. It will certainly prevent infection from the strains it targets, and at the least can save you half the misery of flu season.

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By Emily Willingham



2 responses

18 01 2012
Asian Poker

Post is nicely written and it contains many good things for me.

13 04 2012
Tsu Dho Nimh

“I got a flu vaccine one year and ended up getting the flu anyway. ”

Unless it puts you in bed foe a week with a fever of 102+, feeling like an entire major league baseball team has used you for batting practice, it wasn’t influenza.

I’ve had genuine influenza twice, and it’s really nasty. Next to it, everything else is a bad cold.

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