Contraindications and Precautions of Hepatitis A Vaccine The main contraindication for HepA vaccine is A severe allergic reaction (eg, anaphylaxis) after previous dose or to a vaccine component The main precaution with HepA vaccine is Moderate or severe illness with or without a fever (vaccination is postponed until the illness resolves) Dose and Administration of Hepatitis A Vaccine The HepA vaccine dose is 0.5 mL IM up to age 18 years or 1 mL IM for adults (age ≥ 19 years).