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Indian Journal of Medical Microbiology, Vol. 27, No. 1, January-March, 2009, pp. 48-50 Brief Communication High prevalence of Hepatitis A virus antibody among Bangladeshi children and young adults warrants pre-immunization screening of antibody in HAV vaccination strategy Ahmed M, Munshi SU, Nessa A, Ullah MS, Tabassum S, Islam MN Department of Virology, Bangabandhu Sheikh Mujib Medical University (BSMMU), Shahabag, Dhaka Date of Submission: 10-Jan-2008 Code Number: mb09011 Abstract Serum samples from 465 subjects aged between 1 and 25 years were tested for antibody against hepatitis A virus (HAV) [anti-HAV IgG and IgM] to determine the seroprevalence of HAV antibody and do a cost-benefit analysis for decision making about vaccination against HAV among the general population of Bangladesh. A high prevalence of anti-HAV (74.8%) was observed in the study population; the whole study population was found positive for anti-HAV by the age of 25 years. On performing the cost-benefit analysis, it was found that the cost for vaccination with screening for anti-HAV was almost three times cheaper than vaccination without screening. Thus, in the present socioeconomic condition of Bangladesh, a policy based on screening for HAV antibody before vaccination is recommended.Keywords: Anti-hepatitis A virus (HAV), HAV seroprevalence, HAV vaccine Hepatitis A virus (HAV) infection is endemic in many developing countries including the Indian subcontinent, with 100% seroprevalence in the adult population. [1],[2] This rate is much lower in Western Europe and the USA, [3] indicating that the rate of HAV infection varies among countries and regions. In high endemic areas, children are continuously exposed to the virus, which confers lifelong immunity. [4] Because Bangladesh is a highly endemic country, it is unusual to have HAV infection in adults. However, recently, a good number of cases of HAV infection were diagnosed among the adult population at the Department of Virology, Bangabandhu Sheikh Mujib Medical University (BSMMU), Dhaka (unpublished data). Data on the proportion of the population that is immune or has been infected with a specific virus have many important epidemiologic applications, including the identification of susceptible groups in the population and the evaluation of health programs. [5] In this context, the present study was designed to study HAV antibody in different age categories, both in urban and rural areas, and to perform a cost-benefit analysis study before formulating a vaccination strategy for the general population of Bangladesh. Materials and Methods This prospective study was done from January to July 2005 among hospital outpatients and healthy volunteers from rural areas without any history of acute hepatitis and/or HAV vaccination. The sample size was determined by the prevalence rates of neighbouring countries with a similar socioeconomic condition (e.g., India and Pakistan) as there are no previous data on HAV seroprevalence from Bangladesh. The study population ( n = 465, age: 1 - 25 years, female = 300 and male = 165) was divided into two groups: rural and urban. Because the prevalence of anti-HAV depends on socioeconomic conditions, the urban group was further divided according to their financial income into high (> 100 USD) and low (< 100 USD) socioeconomic groups. With prior written consent, clinical history and relevant data were recorded and 2 mL of blood was collected from the study subjects. Serum was separated and stored at -20 0 C for the test. The competitive ELISA (ETI-HA-IGMK PLUS, DiaSorin, Italy) for anti-HAV (IgG and IgM) was performed at the Department of Virology, BSMMU, Dhaka. The cut-off value was determined by the mean absorbance of the calibrator values. The presence or absence of anti-HAV was determined by comparing the absorbance values of unknown samples with the absorbance values below/above the cut-off values of the controls. For the cost-benefit analysis study, the price for the available HAV vaccine at the marketplace was considered. All data were analysed using commercially available software (SPSS Version 11.5, SPSS Inc. USA). Results The average prevalence of anti-HAV was 74.8% (348/465), which increased gradually with age [Table - 1]. The overall prevalence of anti-HAV in the 1-2 years age group was found to be 15% (3/20) and through a gradual increase in age, the prevalence reached 100% (60/60) in the 21-25 years age group. In the low-socioeconomic category of the urban group, the anti-HAV prevalence was 20% among the 1-2 years age group, which reached 100% in the 11-15 years age group. In contrast, anti-HAV prevalence in the high-socioeconomic category of the urban group was 0% in the 1-2 years age group, but reached 100% at a later age (21-25 years age group). However, in the rural population, the anti-HAV prevalence was 25% in the 1-2 years age group and reached 100% in the 16-20 years age group. In the urban population, the prevalence of anti-HAV at the start of school-going age (6-10 years age group) was 75.2% (103/137), which rose to 80.4% (82/102) in the 11-15 years age group and 98.5% (64 /65) in 16-20 years age group. An abrupt rise was detected in the prevalence of anti-HAV from 1-2 years (15%) to the 6-10 years age group (75.2%), which was statistically significant ( P < 0.05). Anti-HAV was significantly higher in the low-income group (79.2%) in comparison with the high-income group (68.8%) among the urban population ( P < 0.05). When compared, the prevalence of anti-HAV in rural subjects was significantly higher (82.2%) than that from the urban area (73. 3%) ( P < 0.05). The cost of a single anti-HAV ELISA was approximately USD 2.52. A single vaccination for HAV was USD 9.60, while two doses are required in HAV vaccination. The total cost of screening followed by vaccination of the susceptible study population was thus USD 3418, which was almost three times less than the cost of vaccinating without screening [Table - 2]. Discussion In Bangladesh, vaccination against HAV is not included in the Extended Program on Immunization, and currently there is no recommended HAV vaccination strategy in Bangladesh. As such, pre-school and school-going children are usually administered two doses of HAV vaccine on physician′s recommendation or on request from interested persons without prior knowledge of their serostatus. The World Health Organization recommends that epidemiological and cost-benefit studies should be considered before any decision is taken on national policies for HAV immunization. [6] Accordingly, we decided to conduct a serological study on HAV infection for the first time in Bangladesh and found a high prevalence (74.8%) of anti-HAV among Bangladeshi children and adult population. Our study observed that the entire population became positive for anti-HAV on reaching 25 years of age, which is similar to the situation prevailing in other developing countries, [7],[8] but is quite opposite to that of Western Europe and the USA. [3],[9] In order to observe the impact of sanitation, maintenance of hygiene, water supply and other facilities on HAV prevalence, our study population was divided into two major groups: rural and urban. In comparison with the urban population, a significant high prevalence of anti-HAV was found in the rural areas, which was also previously shown in another study. [3] Our study observed that HAV infection started at an earlier age in the low-socioeconomic group of the urban and rural populations than in the high-socioeconomic group of the urban population. Moreover, the whole population, except the high-income group, was infected naturally and acquired natural immunity to HAV by 16-20 years of age [Table - 1]. These differences in prevalence are probably due to improper sanitation, water contamination, overcrowding and poor hygienic and living conditions. [6] Our study also observed that a large number of children (75.2%) of school-going age were naturally immune to HAV and needed no vaccination at all. Furthermore, the total adult population of Bangladesh, irrespective of area of residence and socioeconomic condition were naturally immune to HAV infection. On cost-benefit analysis, it was observed that the cost of vaccination with screening was almost three times cheaper than the cost of vaccination without screening. Therefore, a mass vaccination or vaccination without prior knowledge regarding the serostatus of prospective vaccinees could be an unnecessary immunological assault and may not be a suitable strategy for Bangladesh in lieu of the present socioeconomic condition. The incidence of hepatitis A infection is inversely correlated to living standards and decreases as living standards improve in any country. [10] Thus, vaccination of children under 2 years of age or children of the high-socioeconomic group may seem beneficial, but in the context of the present socioeconomic condition of Bangladesh, the benefits of mass vaccination should be assessed carefully. As mass HAV vaccination of children is recommended only in regions of low endemicity, [11] we suggest a policy for vaccination against HAV based on screening before vaccination, which is cost effective, safe and more rational. It is envisaged that this vaccination strategy will not only target seronegative individuals for preventive vaccination but will also prevent seropositive persons from receiving unnecessary immunization. References
Copyright 2009 - Indian Journal of Medical Microbiology The following images related to this document are available:Photo images[mb09011t2.jpg] [mb09011t1.jpg] |
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