Question: What causes a reaction from the flu vaccine ?? Why does it cause red spots on some people ??

Arthur Dyer answered on 11 Nov 2014:

So there’s a number of different reactions to the flu vaccine which, in a way, are mostly all good signs because it means your body is fighting the virus.

There is one really bad reaction though which is an allergic reaction.

Flu shots are grown in chicken eggs (it sounds weird but it works really well!) and occasionally people can be allergic to the albumen (the white part of the egg) and so injecting them with the flu vaccine causes them to go into shock and that can be pretty dangerous. This is really rare however and most people are fine.

The reactions from a flu shot in a normal person just show that your body has a good immune system.

You’ll often notice where the injection was given there will be lump that is red, warm, swollen and a little painful… these are all classic signs of inflammation and it means that your white blood cells have noticed the virus that you’ve got in your arm and are all rushing to the viruses to kill the virus. Because you have so many white blood cells rushing to that area you get a lump and pain!

You often also get a painful neck and painful armpits and tops of your legs. This is because you have something called lymph nodes in all these places.

Lymph nodes are where our body trains white blood cells to attack the right things and not your own cells. When you get the flu shot you will get a whole bunch of white blood cells going to your lymph nodes to learn what the virus looks like so they can attack it if they see it and these white blood cells will multiply and replicate and this causes the lymph nodes to become really swollen and that causes pain too but these cells stick around for a long time in your blood ready to fight flu when they see it and this is how vaccination works.

So yeah it does cause some side effects but those side effects are exactly what we want to see to protect you!