What exactly is inside a flu shot? Formaldehyde and chicken eggs http://t.co/HOhbvuhcoJ pic.twitter.com/zt4wQltOyu — WIRED (@WIRED) October 14, 2015 ALL FLU VACCINES start with flu viruses: genetic material packaged in an envelope of proteins and fats, studded with yet more proteins—antigens—that push the body’s immune system into action. Manufacturers growContinue Reading