Your Health: 5 Things That Don’t Prove Your Flu Shot Didn’t Work

Getting a flu shot won't help your body fend off the common cold. © Anna Bizoń/iStock /Thinkstock

by Maria Trimarchi | shared from HowStuffWorks |

A flu shot won’t give you superpowers, but it will help you fend off common strains of influenza.

Would you believe that more American adults fear losing a tooth than getting the flu, yet every year as many as 3,300 to 49,000 people in the U.S. alone die from serious flu-related complications [sources: American Association of EndodontistsNeel]?

During flu season each year, anywhere between 5 and 20 percent of Americans will get the flu virus, which will last for about a week (or longer for some symptoms, such as a lingering cough) [source: WebMD]. The only way to prevent it — and there’s really no way to prevent it 100 percent of the time — is with a flu vaccination (shot or nasal spray). The Centers for Disease Control and Prevention (CDC) recommends that everyone ages 6 months and older be vaccinated every year, yet fewer than 50 percent of Americans get a flu shot [source: Bernard-Kuhn].

What if you were one of those who did get your annual flu shot, but your aches, fever and fatigue would suggest otherwise? Why does it sometimes feel like this year’s flu shot didn’t work? Despite your sore throat and stuffy nose, don’t be so quick to dismiss the vaccine as bunk.

You Run a Fever and Feel Achy Afterward

That general achy feeling, nausea and low-grade fever that developed soon after you got your flu shot isn’t an indication that your attempts at preventing this year’s flu failed — it’s actually to be expected. Wait, expected? These are normal side effects in many people, caused by the body’s immune system responding to a foreign invader. Additionally, the flu shot may leave your arm feeling sore, and there may or may not be some redness and swelling where the shot was given. All of these side effects should be mild and should only last about a day or two — not too bad of a trade-off when we’re talking about a day with a sore arm compared to a week of full-blown flu.

You Get Your Flu Shot Too Late

The CDC recommends we all get our flu shot as soon as our doctor or local clinics begin to offer the vaccination, usually in the early autumn, in an effort to protect each of us before flu season officially hits. If you wait until you see headlines about a major flu season underway (or your coworkers and family members start coming down with it), there’s a real chance you could be infected before that last-minute shot really starts to protect you. It takes more than a week or two for the benefits of the vaccination to take effect, so there’s the possibility that you could get your shot and then develop influenza if you were exposed to the virus either just before or after your vaccination.

So, your odds of preventing the flu from keeping you down increase if you’re vaccinated early in the flu season, but the window of opportunity is much larger than you might think. Getting your influenza vaccine sometime between Labor Day and Thanksgiving is considered ideal, but flu season doesn’t typically peak until January, February or March — some seasons it’s been known to last through May. And a late shot is better than no shot, so no matter whether it’s October or February, the vaccine can still help.

You Catch a Cold

You’ve been sneezing, you have a sore throat and you’re beginning to develop a bit of a cough; don’t be disappointed that this year’s flu shot failed you — it’s likely you’re suffering something other than the flu. The common cold is often confused for the flu, but the two illnesses aren’t caused by the same thing. Additionally, only strains of the influenza virus are included in the flu vaccine. There are a few respiratory illnesses that can look a lot like colds and flu, despite being neither.

Respiratory syncytial virus (RSV), respiratory adenoviruses and parainfluenza viruses also cause upper respiratory illnesses that feel a lot like having the flu. RSV, for instance, usually develops as a cough with a stuffy nose, sore throat, earache and fever, and it can cause other conditions such as pneumonia and bronchitis. Adenoviruses also may cause respiratory infections such as pneumonia, as well as conjunctivitis (pink eye). And parainfluenza viruses are a common cause of croup in kids.

You Get Norovirus

Influenza gets blamed for a lot of ailments that it doesn’t actually cause; for example, the “stomach flu.” There really isn’t such a thing as stomach flu. The flu doesn’t involve vomiting or any other gastrointestinal distress — it’s a respiratory illness that’s caused when you come in contact with a human influenza virus. Noroviruses, however, do cause stomach flu symptoms; nausea, vomiting, diarrhea and abdominal pain are all classic norovirus complaints — and you may also have a fever, headache or general body aches (which might make you think you have influenza). Norwalk, Snow Mountain and Hawaii noroviruses account for an estimated 90 percent of all cases of so-called stomach flu worldwide — and about 20 million infections annually among Americans [source: Nordqvist].

You Get the Flu

This may come as a surprise to many, but you can’t get the flu from the flu vaccination itself. You just can’t; the virus is in the vaccination is inactivated (that mean’s it’s been killed). You can’t get it from the nasal spray, for that matter, either. But despite this, many people’s personal experience sometimes suggests otherwise. There’s a good reason for this happening, though, and it’s not the fault of the vaccination; it’s your body. It takes two weeks, give or take a day or two, after you’ve been vaccinated for your body to build up a level of antibodies great enough to protect itself against the flu when you are exposed, but in the meantime you’re just as vulnerable as you were the day before you got vaccinated. Plus, the flu vaccine can only protect you from the known strains of the flu that were around when the vaccine was formulated. If a new strain develops, you won’t be covered.


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