Normal human immunoglobulin, containing at least 100 international units (IU)ml-1 of anti-HAV antibody, given intramuscularly before exposure to the virus or early during the incubation period will prevent or attenuate a clinical illness. The dosage should be at least 2IU of anti-HAV antibody kg "i body weight, but in special cases, such as pregnancy or in patients with liver disease, that dosage may be doubled.
Immunoglobulin does not always prevent infection and excretion of HAV and inapparent or subclinical hepatitis may develop. The efficacy of passive immunisation is based on the presence of HAV antibody in the immunoglobulin and the minimum titre of antibody required for protection is believed to be about 10IUl~i.
Immunoglobulin is used most commonly for close personal contacts of patients with hepatitis A and for those exposed to contaminated food. It has also been used effectively for controlling outbreaks in institutions such as homes for the mentally handicapped and in nursery schools. Prophylaxis with immunoglobulin is recommended for persons without HAV antibody visiting highly endemic areas. After a period of 6 months the administration of immunoglobulin for travellers needs to be repeated, unless it has been demonstrated that the recipient had developed HAV antibodies. Active immunisation for travellers is therefore preferred and is strongly recommended.
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