Less severe forms of immediate hypersensitivity reactions can occur, including rash or urticaria. Yellow fever vaccine can rarely cause anaphylaxis. The Vaccine Adverse Event Reporting System (VAERS) data from 2000–2006 indicate a reporting rate for anaphylaxis of 1.8 cases per 100,000 doses administered.
Hypersensitivity reactions are thought to occur in response to egg protein, chicken protein, or gelatin that are present in the vaccine as a result of the production process. Also, the stopper of the vaccine vial contains dry natural latex rubber that may cause an allergic reaction.
Because anaphylaxis has been reported to occur in people with no prior history of reactions to the vaccine components, all yellow fever vaccine recipients should be observed for at least 15 minutes following vaccination. All providers administering the vaccine should be prepared to rapidly recognize and treat this life-threatening reaction. Injectable epinephrine and equipment for maintaining an airway should be available for immediate use, in accordance with the General Recommendations of the ACIP.