What causes a swollen arm after a flu shot?

If the swelling is localized around the injection site, this is a common occurence. The flu vaccine is given in a muscle…In this case, the deltoid muscle. Occasionally the injected liquid will form a “ball” in the muscle instead of dispersing throughout the muscle. You can massage it lightly to break this up. read more

It’s a typical autoimmune response. Something poked your arm, so your immune system goes on high alert trying to prevent any pathogens from entering your body via that poke. The vaccine probably has dead pathogens in it (depending on the vaccine type) so your immune system heats up again, but then realizes that this is a false alarm. read more

The most common side effect of the flu shot is a reaction at the injection site, which is typically on the upper arm. After the shot is administered, you may have soreness, redness, warmth, and in some cases, slight swelling. read more

After receiving this year’s flu shot on 2/6 at my local Walgreen’s pharmacy, within a few hours of getting the shot, I developed a sharp pain in my arm a few inches down from the injection site and on the inside of my arm. read more

Swelling of the arm after a routine vaccination usually begins the first day after your child receives the shots. Most often, the swelling recedes on its own within a few days. The DTaP immunization for diphtheria, tetanus and pertussis may cause soreness and swelling for a bit longer or up to one week post-vaccination. read more