Vaccination Against Hepatitis A And B
Hepatitis A and B are diseases that can be prevented by vaccination. Hepatitis A does not progress to chronic infection, but morbidity and economic cost are considerable. Two Hepatitis A Vaccines Havrix and VAQTA are available in the market and have protective efficacy of 94% to 100%. Because of cost however, in communities with high endemicity of Hepatitis A and high levels of lifelong natural immunity, it is more cost efficient to screen potential vacinees first to see if they are already immune.
The vaccines are given intramuscularly in a two-dose regime 6 months apart. More than 95% of vacinees >2 years old develop anti-HAV within one month of a single dose and 100% develop immunity after a second dose. Immunity may last 20-30 years.
Routine immunisation is recommended for children living in areas where Hepatitis A is of low endemicity, but where it is more than 2 times the national average. This situation occurs in many western countries. Other indications are persons who come from low endemicity countries travelling to or working in countries or areas with high or intermediate endemicity of Hepatitis A, during outbreaks of epidemics in communities with already high or intermediate endemicity, day care centre children and employees, residents and staff of institutions for the mentally retarded, people with chornic liver disease, military personnel, health care workers, food handlers, sewage workers and sexually active homosexuals.
Hepatitis B is responsible for acute and chronic liver disease and death from liver failure or liver cancer. A reservoir of virus can be found in as high as 20% of some communities and this is sustained mostly by vertical transmission. Neonatal and childhood infection often progresses to chronicity. The only certain way to prevent a large Hepatitis B related disease load in a community is to immunise all newborns, children and susceptible young adults and other high-risk groups. Almost all countries in the Asia Pacific region have introduced national immunisation programmes.
There are plasma derived and yeast derived recombinant DNA available on the market, all of high immunogenicity at the doses recommended. The vaccines have protective efficacy of >90% and remain above the critical threshold for protection for over 10 years. Screening for previous infection and natural immunity before vaccination is recommended in areas of high prevalence of Hepatitis B infection, as the vaccination is expensive. The vaccination is given intramuscularly at months 0, 1 and 6. Post vaccination testing of immunity levels should be carried out for those groups for whom it is important to be sure that they have attained immunity. Low or non responders can be given repeated booster doses, higher doses or changing to plasma derived vaccine which is reportedly more immunogenic. Vaccine failure is more likely in immunocompromised or elderly people.
Hepatitis B vaccination is recommended for all infants and as soon as possible in regions where the prevalence of Hepatitis B is high, high risk groups such as persons who come into contact with blood or blood products, drug abusers and individuals requiring transfusions of blood or blood products, such as haemophiliacs. Inmates in institutions for the mentally subnormal, promiscuous persons, close contacts of patients with chronic Hepatitis B and travellers to endemic areas should also be considered for vaccination.
Combination vaccines against Hepatitis A and B are commercially available and are convenient for those who have immunity to neither and for whom vaccination against both are appropriate.