The flu is a respiratory virus that is spread when people cough, sneeze, talk and wipe their nose leaving little droplets for others to pick up or breathe in.
It can spread quickly as an entire family in a household, all the children in a daycare, or all the adults at a workplace pass it from person to person, making many ill and feeling miserable.
The most common symptoms are quite familiar: fever, cough, congestion, body aches, sore throat, fatigue, and headaches or lightheadedness.
In attempt to avoid contracting the flu, many people opt to receive either the trivalent (H1N1, H3N2 and influenza B virus) or the quadrivalent (two types of influenza A and 2 types of influenza B) flu vaccine.
Like many vaccinations, the injection is done in the upper arm and can cause pain and swelling at the site.
The reasons for this vary.
Pain may arise because you are receiving an injection into your muscle where the inactivated flu virus plus thimerosal (a mercury-based preservative), aluminum salts, sugars, gelatin, egg protein, formaldehyde, and neomycin (residual antibiotic) are inserted.
This alone can cause local pain and swelling as the muscle in your arm is not happy.
When those ingredients are injected, your immune system kicks in and comes over to check out what was just put into the muscle. This leads to a clean-up of the area by your immune system, and the creation of antibodies against the inactivated flu strains.
Hopefully this will protect you, should you come in contact with those contagious respiratory droplets from an infected person. With your immune cells all fired up in the muscle of the upper arm, you may experience pain and swelling, and sometimes a heated or hot sensation of the skin.
Thankfully, most adverse reactions are mild and short-lived. However, in some instances they can result in long-lasting pain and numbness in the arm.
Commonly recommended treatments for those who experience side effects include over-the-counter pain medications like ibuprofen or acetaminophen, heat or ice, and rest.