Updated: Sep 14, 2019
There is a very common myth out there that if you get the flu shot, that it may give you the flu instead of preventing it. This is simply not how the flu shot works. This mindset is due to a lot of misconceptions that many people have about the flu shot; and since flu season is just around the corner, it is probably best to clear up some of these misconceptions.
What is the flu shot and can it give you the flu?
These vaccines are made with inactivated or killed viruses. The inactivated virus still possess qualities that allow the immune system to produce a defense against it. This inactivated version however does not have the ability to infect cells; so, it is not functional enough to make anyone sick. The CDC confirms:
"...flu vaccines cannot cause flu illness... the vaccine is made either with a) flu viruses that have been ‘inactivated’ (killed) and that therefore are not infectious, or b) using only a single gene from a flu virus (as opposed to the full virus) in order to produce an immune response without causing infection. "
So, there is no need to worry about getting the flu via a vaccine, but you can still develop an immune response. This is one of the reasons why some people think the shot gave them the flu.
Are flu shots 100% effective?
Actually, no. According to Mayoclinic, the flu shot is only about 50% effective on average. This is due to a variety of reasons. In some cases, the particular strain of flu virus that one catches may not exactly match the inactivated virus in the vaccine. Despite such a mismatch, often times, the immune response is adequate enough to combat various flu strains and/or even reduce the symptoms if you do get it.
It should also be noted that it takes about 2 weeks after taking the flu vaccine to be protected against it. This is due to your body creating defenses to antigens to fight off the flu in case you come in contact with it later. So it is possible to catch the flu before the vaccine kicks in.
Why should I get a flu shot?
Well, the main reason is that the flu can be life-threatening, especially to vulnerable populations. The more people that are vaccinated, the more we protect others. This is called Herd Immunity. So you are not just getting vaccinated for yourself, but also for people around you who may be too young or unable to get vaccinated themselves. It is important for society as a whole and helps to prevent future outbreaks.
Here is a video discussing more about vaccines and the immune system from CrashCourse: