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Age in Guiding Strategy in Hepatitis A Vaccination

      To the Editor:
      We read with interest the review articles on hepatitis A virus (HAV) vaccination in The American Journal of Medicine.
      • Poland G.A.
      Evaluating existing recommendations for hepatitis A and B vaccination.
      • Jong E.C.
      United States epidemiology of hepatitis A: influenced by immigrants visiting friends and relatives in Mexico?.
      The Centers for Disease Control and Prevention (CDC) recommended that HAV vaccination be administered to individuals living in states and communities with consistently elevated rates of HAV.
      Singapore is a small country with a population of about 4 million, situated at the center of Southeast Asia. With good socioeconomic development and public health measures, seroprevalence of HAV in Singapore was reduced from almost universal for those above age 30 years in 1975, to less than 50% of those above age 40 years in 1991.
      • Goh K.T.
      • Wong L.Y.
      • Oon C.J.
      • Kumarapathy S.
      The prevalence of antibody to hepatitis A in Singapore.
      • Fock K.M.
      • Tay H.H.
      • Phua K.B.
      • et al.
      Seroprevalence of antibodies against hepatitis A (anti-HAV) in Singapore: the NFDD experience.
      The latest epidemiological figures show a low incidence of HAV infection, at 2.4 per 100,000 population.

      Singapore National Environment Agency. Annual Report 2000. Available at: http://www.nea.gov.sg/cms/ccird/pg_54_63.pdf. Accessed April 4, 2006.

      However, as Singapore also is surrounded by highly endemic countries, vaccination against HAV is recommended.
      The CDC also recommended that prevaccination testing for prior exposure to HAV be considered in endemic areas to reduce costs by not vaccinating persons who have prior immunity. The cost-effectiveness of prevaccination screening depends on factors such as the expected prevalence of immunity, cost of vaccination versus cost of serologic testing, and the likelihood that testing will not interfere with initiating vaccination.
      Centers for Disease Control and Prevention
      Prevention of hepatitis A through active or passive immunization: recommendations of the Advisory Committee on Immunization Practices (ACIP).
      We recently performed a seroprevalence survey among 382 subjects who attended a public education symposium on liver diseases. Mean ± SEM of age was 50.7 ± 0.7 (median 52, range 12-84) years. Only 25 (6.5%) had prior HAV vaccination. We found 220/358 (58%) positive for anti-HAV IgG. Individuals with prior immunity to HAV were more likely than those without prior immunity to be older (age 55 ± .7 vs 44.0 ± 1.1 years, respectively, P <.001), and to be positive for hepatitis B surface antigen (11% vs 5%, respectively P = .041). At multivariate analysis, age was the only significant factor associated with HAV immunity.
      When age was plotted against HAV immunity on the receiver operating characteristic (ROC) curve, a cut-off age of 40 years could be identified (Figure). At age <40 years, only 20% had prior immunity, so prevaccination testing might be unnecessary. At age >40 years, 67% had prior immunity, so prevaccination testing should be considered.
      Figure thumbnail gr1
      FigureROC curve showing age versus prior immunity to Hepatitis A virus.
      At our hospital, the costs of testing for anti-HAV IgG and dual doses of HAV vaccination (HARVIX, GlaxoSmithKline Pte Ltd, Singapore) are US$26 and USD$113, respectively. For this cohort of 382 patients, the strategy of vaccinating all would cost US$43,166. Testing all and then vaccinating those without immunity would cost US$44,464. But testing only those aged >40 years and vaccinating those without immunity and all <40 years would only cost US$27,661.
      Our study results suggest that age is an important predictor of prior HAV immunity and can be used as a determining factor in guiding HAV vaccination strategy. Using age as a guide could help to improve the cost-effectiveness of HAV vaccination within a community.

      References

        • Poland G.A.
        Evaluating existing recommendations for hepatitis A and B vaccination.
        Am J Med. 2005; 118: 16-20
        • Jong E.C.
        United States epidemiology of hepatitis A: influenced by immigrants visiting friends and relatives in Mexico?.
        Am J Med. 2005; 118: 50S-57S
        • Goh K.T.
        • Wong L.Y.
        • Oon C.J.
        • Kumarapathy S.
        The prevalence of antibody to hepatitis A in Singapore.
        Asia Pac J Public Health. 1987; 1: 9-11
        • Fock K.M.
        • Tay H.H.
        • Phua K.B.
        • et al.
        Seroprevalence of antibodies against hepatitis A (anti-HAV) in Singapore: the NFDD experience.
        Singapore Med J. 1995; 36: 26-27
      1. Singapore National Environment Agency. Annual Report 2000. Available at: http://www.nea.gov.sg/cms/ccird/pg_54_63.pdf. Accessed April 4, 2006.

        • Centers for Disease Control and Prevention
        Prevention of hepatitis A through active or passive immunization: recommendations of the Advisory Committee on Immunization Practices (ACIP).
        MMWR Recomm Rep. 1999; 48: 1-37

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      • The Reply
        The American Journal of MedicineVol. 120Issue 8
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          As discussed in our paper,1 hepatitis A and B vaccines are widely available. Unfortunately, neither vaccine is used to its greatest extent with existing expert recommendations not closely adhered to and too few at-risk persons receiving these vaccines. Equally frustrating is that current recommendations do not cover all those who are at risk. In particular, the Advisory Committee on Immunization Practices recommendations for the use of hepatitis A vaccine in all persons, and for hepatitis B vaccine in adults, remain risk-based – a failed strategy that was abandoned by hepatitis B vaccination programs for children.
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