My flu shot didn't work this year.
— Steve Martin (@SteveMartinToGo) November 25, 2013
The last thing we want to do is pick a fight with the legendary Steve Martin, but we have to respectfully disagree with his assessment. The idea that your flu shot "didn't work" is one that is constantly perpetuated by people young and old, right up there with the other most common flu shot myths. This line of reasoning is responsible for thousands of people skipping their flu shot every year, a decision that can have serious consequences. Before you dismiss the vaccine as worthless or unnecessary, consider the following five explanations for your experience: 
1.) You caught a different strain of flu than the one in this year's vaccine.
The flu virus mutates very rapidly and there are dozen different strains and combinations. The trivalent and quadrivalent vaccines are developed to protect against the three to four strains that are most likely to be circulating that year. Even when the vaccine is a close match to that year's influenza distribution, it's still possible to catch one of the other strains of flu. In any given year, on average, flu vaccines are about 60 percent effective at preventing influenza among the general population.
2.) You're suffering from something other than the flu.
The CDC notes that 75 percent of the illnesses people get after they’re vaccinated are not influenza, but are caused by other viruses such as rhinoviruses, coronaviruses, and dozens more. Influenza takes the fall for a lot of sicknesses that it doesn't actually cause. Take the "stomach flu," for example -- there is no such thing! The flu doesn't involve gastrointestinal distress or vomiting. It's easy to blame influenza because it's so prevalent, but consider your symptoms or see your primary care physician if you aren't sure what you're suffering from.
3.) You got the flu within two weeks of getting your flu shot.
Most people think the flu vaccine offers immediate protection, but this isn't the case. Flu vaccines cause antibodies to develop in the body about two weeks after vaccination. During that time, it's possible that you've already caught the virus. This is one of the main reasons that some individuals feel like the "flu shot gave me the flu."
4.) You're experiencing side effects from the vaccine.
The side effects of a flu shot are occasionally mistaken for something more serious. Many individuals experience full body aches, slight nausea and a low-grade fever after receiving the flu vaccination. This doesn't mean that the shot didn't work -- it's actually a very normal reaction that is a sign that your immune system is fighting off a foreign invader. Any side effects should be mild and should only last a day or so; any longer than that warrants a call to your doctor.
5.) You developed less immunity.
While the flu vaccine is the absolute best way to prevent the flu, effectiveness can vary widely depending on who is being vaccinated (in addition to how well matched the flu vaccine is with circulating strains). In general, the flu vaccine works best among healthy adults and older children. Some older people and people with certain chronic illnesses might develop less immunity than healthy children and adults after vaccination. However, even for these individuals, the flu vaccine still may provide some protection, so you would've had a much worse experience with the flu without the shot.
Regardless of where you fall on the flu shot debate spectrum, nobody suggests skipping the vaccine entirely and fighting off an influenza infection on your own. The flu puts hundreds of thousands of people in the hospital each year and is responsible for anywhere between 3,000 to 49,000 deaths, many of those young, healthy individuals. Don't gamble with your health -- get your flu shot today.
