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Vol. 3, No. 2 April 1995 |
Prevention of Hepatitis A
The Disease:
Hepatitis A (HAV) is one of a number of "alphabetical" viruses ( A to E) which infects the liver, causing diffuse hepatocellular damage. Clinical signs and symptoms of hepatitis A are age dependent. Young children are often asymptomatic(less than 10 % under 6 years of age develop typical illness with jaundice) whereas, the majority of adults develop fever, malaise, nausea and jaundice.
The overall mortality rate from Hepatitis A is low, about 0.2%, but in adults over 50 years it is 3 %. The usual incubation period for hepatitis A is one month, with a range of 15-50 days. There is no chronic carrier state with the disease, and a single infection is believed to result in lifelong immunity.
Transmission:
Hepatitis A is most frequently transmitted by the fecal-oral route. Risk factors for acquiring hepatitis A in North America include, in descending order, person-to-pereson contact, ingestion of contaminated food and water employment at a health care facility or day-care center, poor hygiene or living under unsanitary conditions, and travel to developing countries.
Prevention and Control:
The most important measures used to prevent hepatitis A are good personal hygiene, adequate food handling practices, availability of clean drinking water and proper sanitary facilities. Additional control measures include passive immunization with immune globulin and active immunization with hepatitis A vaccine.
Immune serum globulin:
Human serum immune globulin(gamma globulin) has shown considerable effectiveness in pre-exposure prophylaxis, however, protection tends to be short-lived. When pre-exposure prophylaxis is indicated, such as for travel to developing countries, a single intramuscular dose of 0.02 ml/kg will provide up to three months of protection; 0.06 ml/kg will protect for 4-6 months.
Hepatitis A vaccine:
In August, 1994, an inactivated hepatitis A vaccine was licensed in Canada. The vaccination schedule consists of two intramuscular doses one month apart and a booster -12 months later. Results from clinical trails show that 96%, 99.8% and 100% of vaccinees develop antibodies after the first, second and third (booster) dose respectively. Duration of immunity following vaccination is as yet unknown but is estimated to be at least three years and likely to be as long as 10 years.
The national Advisory Committee on Immunization (NACI) recommends the hepatitis A vaccine for the following individuals:
A. High priority for vaccination:
i. residents of communities with high endemic rates or recurrent outbreaks of Hepatitis A
ii. long stay residents or travellers e.g. missionaries, diplomats etc.
iii. those who travel repeatedly and/or to rural areas
iv. residents and staff of institutions for the developmentally challenged
v. hemophiliacs
vi. primate handlers
B. Moderate priority for vaccination:
i. inmates of correctional facilities where HAV control is a problem
ii. male homosexuals with multiple sexual partners
iii. illicit drug users living in unsanitary conditions
C. No clear need for vaccine use:
i. Child day-care facilities
ii. health care workers
iii. sewerage workers
iv. food handlers
Guest Writer: Dr. J. Keystone
Selected Bibliography:
1. National Advisory Committee on Immunization (NACI). Statement on the prevention of Hepatitis A infection. Can Dis Comm Rep 1994;20: 133-136
2. Yuan L. Hepatitis A: prospects for control. Can Family Physician 1995 (inpress)
3. Immunization Practices Advisory Committee (ACIP) Protection against viral hepatitis. MMWR 1990; 39: (Suppl) 1-26
4. Kendall BJ and Cooksley WGE. Prophylactic treatment regimens for the prevention of Hepatitis A. Drugs 1991; 41: 883-888
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