Use of hepatitis A vaccine for post-exposure prophylaxis in individuals over 40 years of age: A systematic review of published studies and recommendations for vaccine use.

Introduction: Hepatitis A can cause widespread outbreaks. Until 2018, postexposure prophylaxis (PEP) in the United States for individuals >40 years consisted of immune globulin (IG) administered as soon as possible after exposure, ideally within 14 days whereas those aged ≤40 should receive hepatitis A (HepA) vaccine. However, state health departments reporting difficulty quickly accessing and administering IG, costs of higher IG doses and importance of long-term HAV protection prompted CDC to review immunogenicity data for use of HepA vaccine for PEP in older adults. We reviewed literature on use of HepA vaccine in adults >40 years and existing recommendations for HepA vaccine for use as PEP in other countries.

Methods: We searched PubMed and EMBASE from January 1, 1992-January 7, 2017 using the terms "hepatitis A vaccine∗" and "HAV vaccine∗." Two reviewers read each abstract and articles were preserved if they included results (seroprotection, mean titers) within 28 days of HepA vaccine administration in adults >40 years. Additionally, we reviewed PEP recommendations from six other jurisdictions.

Results: A total of 1,039 unique articles were identified, of which eight were retained and two added from references. Three studies included direct comparisons between individuals aged >40 years and those ≤40 years and one other study included three age groups over 40 years, finding lowest immunogenicity in the oldest adults. All found higher proportions seroprotected (definition varied by study) in younger age groups (ages varied by study) at 15 days post-vaccination but similar seroprotection at 30 days. Most other jurisdictions reviewed recommended vaccine alone or in conjunction with IG for PEP in older adults.

Conclusions: Immunogenicity of HepA vaccine may be diminished in older adults, especially in the very oldest age groups. HepA vaccine should be administered as soon as possible within 14 days after exposure to achieve the best possible immune response.