Genel Bilgiler

introduction

The incidence of hepatitis A is closely related to socioeconomic development, and sero-epidemiological studies show that prevalence of anti-HAV antibodies in the general population varies from 15% to close to 100% in different parts of the world. An estimated 1.5 million clinical cases of hepatitis A occur each year.

In young children HAV infection is usually asymptomatic whereas symptomatic disease occurs more commonly among adults. Infection with HAV induces lifelong immunity.

Currently, four inactivated vaccines against HAV are internationally available. All four vaccines are safe and effective, with long-lasting protection. None of the vaccines are licensed for children less than one year of age.

In countries highly endemic for hepatitis A, almost all persons are infected in childhood with the virus without showing symptoms, effectively preventing clinical hepatitis A in adolescents and adults. In these countries, large-scale vaccination programmes are not recommended.

Transmission occurs primarily through the faecal-oral route, and is closely associated with poor sanitary conditions. Under favourable conditions HAV may survive in the environment for months.

The average incubation period is 28 days, but may vary from 15–50 days. Approximately 10–12 days after infection the virus can be detected in blood and faeces. In general, a person is most infectious from 14–21 days before the onset of symptoms, through to 7 days after the onset of symptoms. 

The risk of developing symptomatic illness following HAV infection is directly correlated to age. In children below six years of age, HAV infection is usually asymptomatic, with only 10% developing jaundice. Among older children and adults, infection usually causes clinical disease, with jaundice occurring in more than 70% of cases. Therefore, highly HAV-endemic regions are characterized by asymptomatic childhood infection, with only the occasional occurrence of clinical hepatitis A.

hepatitis A vaccine

Several inactivated or live attenuated vaccines against hepatitis A have been developed, but only four inactivated hepatitis A vaccines are currently available internationally. All four vaccines are similar in terms of efficacy and side-effect profile. The vaccines are given parenterally, as a two-dose series, 6-18 months apart. The dose of vaccine, vaccination schedule, ages for which the vaccine is licensed, and whether there is a paediatric and adult formulation varies from manufacturer to manufacturer. No vaccine is licensed for children younger than one year of age.

A combination vaccine containing inactivated hepatitis A and recombinant hepatitis B vaccines has been licensed since 1996 for use in children aged one year or older in several countries. The combination vaccine is given as a three-dose series, using a 0, 1, 6 month schedule. 

Hepatitis A vaccines are all highly immunogenic. Nearly 100% of adults will develop protective levels of antibody within one month after a single dose of vaccine

Although one dose of vaccine provides at least short-term protection, the manufacturers currently recommend two doses to ensure long-term protection. In studies evaluating the duration of protection of two or more doses of hepatitis A vaccine, 99%–100% of vaccinated individuals had levels of antibody indicative of protection five to eight years after vaccination. Kinetic models of antibody decay indicate that the duration of protection is likely to be at least 20 years, and possibly lifelong.

The current vaccines are well tolerated and no serious adverse events have been statistically linked to their use. Contraindications to hepatitis A vaccination include a known allergy to any of the vaccine components. Hepatitis A vaccine may be administered with all other vaccines included in the Expanded Programme on Immunization and with vaccines commonly given for travel.

Concurrent administration of immune serum globulin does not appear to influence significantly the formation of protective antibodies.

Table. Recommended Doses and Schedules for Inactivated Hepatitis A Vaccines

IM indicates intramuscular.

Side effects:

Pain/redness/swelling at the injection site, fever, and headache may occur. Less common side effects may include bruising/itching at the injection site, pain/stiffness in the arm/shoulder/neck, sore throat, tiredness, weakness, muscle/joint aches, cold symptoms, nausea, vomiting, loss of appetite, abdominal cramps, diarrhea, irritability, agitation, and trouble sleeping. If any of these effects persist or worsen, tell your doctor or pharmacist promptly.

PRECAUTIONS:

Before getting hepatitis A vaccine, tell your doctor or pharmacist if you are allergic to it; or to neomycin or formalin; or if you have any other allergies.Before using this medication, tell your doctor or pharmacist your medical history, especially of: bleeding problems (e.g., hemophilia, low platelets, anticoagulant treatment), current illness with fever.If you have decreased immune function from other medications (see also Drug Interactions) or other illness (e.g., HIV, leukemia, lymphoma, other cancer), your body may not make enough antibodies to protect you from hepatitis A infection. Antibody levels should be checked after the vaccine series.

During pregnancy, this medication should be used only when clearly needed.