Hepatitis A virus (HAV) is a member of the picornavirus family that includes the human enteroviruses and rhinoviruses. It is a non-enveloped virus of 27-28 nm diameter and all human isolates of hepatitis A belong to a single serotype. The virus has a world-wide distribution and causes about 1.5 million cases of clinical hepatitis each year. Almost all adults in developing areas of the world have serological evidence of infection with HAV. Humans are the only reservoir of HAV, with transmission occurring primarily through the faecal-oral route and closely associated with poor sanitary conditions. Bloodborne transmission of HAV occurs, but is much less common.
The risk of developing symptomatic illness following infection is age related; only about 10% of children develop jaundice following infection, whereas it occurs in more than 70% of older children and adults. Although hepatitis A is mostly self-limiting, the disease may represent a substantial economic burden, particularly in countries with low and intermediate incidence rates where childhood exposure is less common. Epidemiological evidence in humans and in in vitro and in vivo studies support the concept that antibodies to HAV induced by any isolate of the virus will protect against all virus strains. Protective antibodies against HAV develop in response to infection and may persist for life; no specific antiviral therapy effective against HAV is currently available.
Hepatitis A Vaccines
Hepatitis A virus can be grown in cell culture and sufficient amounts of the virus can be obtained for vaccine production. The virus is propagated in human fibroblasts or human diploid cell cultures, purified from cell lysates, inactivated with formalin, and adsorbed to an aluminum hydroxide adjuvant or a virosome consisting of phospholipids vesicles spiked with influenza haemagglutinin and neuraminidase. 2-phenoxyethanol (2-PE) is included as a preservatives in the formulation of some vaccines. Hepatitis A vaccines in combination with hepatitis B or typhoid are commercially available.
Hepatitis A Vaccine Standardization
WHO recommendations for the production and quality control of inactivated Hepatitis A vaccines were published in 1995.
A WHO reference material for inactivated hepatitis A vaccine is available to qualified applicants: