From the CDC:
What is thimerosal?
Thimerosal is an ethyl mercury-based preservative used in vials that contain more than one dose of a vaccine (multi-dose vials) to prevent germs, bacteria and/or fungi from contaminating the vaccine.
https://www.cdc.gov/flu/protect/vaccine/thimerosal.htm
There are 7 ingredients in a flu shot.
1) the (dead) viruses which are the actual vaccine.
2) formaldehyde, inactivates toxins that may have been formed during production
3) Aluminum salts, helps body build stronger immunity
4) Thimerosal, preservative
5) chicken egg protein, helps virus grow during production. 6) gelatin, stabilizer
7) antibiotics, prevent bacteria from growing during production and storage.
Our friend had an allergic reaction to the antibiotics.
Treatment was intraveneous Benadryl with follow up with pill form.