How does a flu shot work?

Feel that autumn chill in the air? That's a tell-tale sign that cold and flu season is here. And, as much as you don't want to hear this, one of the most important steps you take this fall is to get a flu shot.

With countless public health initiatives and medical professionals advocating for this important step, you may wonder how a shot can protect against a seasonal illness in the first place. What many people don't know is that the flu vaccine is different each year, but protects against the flu virus through the same process since immunizations were invented.

Let's dive in to explore how flu shots work and what you should expect for cold and flu season in 2017-2018.

How was the flu shot developed?

First, let's dive into a little history. According to The Guardian, it wasn't until the massive influenza outbreak occurred in Europe from 1918-19 that researchers began to re-examine the source of the condition.

It had long been theorized that influenza was caused by a bacterial infection. But after the pandemic subsided, the United Kingdom's Medical Research Council funded a sustained campaign that culminated in the 1933 discovery of the virus.

The researchers, Wilson Smith, Christopher H. Andrewes, and Patrick Laidlaw, extracted nasal and throat fluids from a sick patient and passed them along to lab ferrets. In less than 48 hours, the ferrets began to exhibit flu symptoms, leading the team to conclude that influenza was caused by a virus rather than bacteria.

We know, it's not exactly a pleasant story, but it gets better. These groundbreaking findings led to the development of the first flu vaccine in 1938 by Thomas Francis and Jonas Salk, who was also the father of the polio vaccine. These rudimentary vaccines were first used to immunize American soldiers during World War II, according to

So why do you need a flu shot every year?

As scary as it might sound, it's important to get an annual flu shot, because these vaccines are one of the only immunizations that are continually updated. Influenza is a rare virus that changes and evolves, sometimes within the same flu season!

According to the U.S. Centers for Disease Control and Prevention (CDC), flu shots work by introducing the seasonal strains into the body, at which point the body's immune response produces antibodies to ward off the infection. It takes about two weeks for these antibodies to form, which is why it's so important to get your flu shot early in the season!

For 2017-18, the CDC recommends the use of injectable flu vaccines, as opposed to the nasal spray flu vaccine, which will not be effective this flu season. Traditional flu vaccines are called "trivalent vaccines," which protect against three strains of influenza:

  • Influenza-A (H1N1) virus
  • Influenza-A (H3N2) virus
  • Influenza-B virus

Quadrivalent vaccines are also available, which protect against the same viruses as the trivalent vaccine, with an additional B virus included. There are also additional options for those 65 and older or pregnant, so consult your doctor to find the best option for your age and current state of health.

Yeah, that's a lot of material to digest in one sitting. But we'll continue posting seasonal updates here, to ensure you stay on top of the latest cold and flu information all year round.

And, as always, treat and prevent seasonal ailments (and maximize your flexible spending benefits) by shopping at, featuring the largest selection of FSA-eligible products on the web!


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