COMMENT
HAV is a hepatotropic virus with faecal–oral transmission and a spectrum of illness varying from asymptomatic transaminase elevation to acute liver failure. It has an incubation period of 15–50 days. Excretion of the virus in the faeces in large amounts and its physical stability contribute to the high potential for household transmission of this infection and occurrence of common source outbreaks of hepatitis A (HA). The infection is milder and less often symptomatic in children than in adults (~30% v. 70%).
   This study showed that HA vaccine is as effective as IG in preventing HA in household and daycare contacts of patients with HA, when administered within 2 weeks after exposure to HAV. This report has led the US Advisory Committee on Immunization Practices to change its recommendation for post-exposure prophylaxis of HA; it now favours HA vaccine over IG.1,2
   Though this study showed the HA vaccine to be as effective as IG, it lacked a placebo group. However, in another study, HA vaccination within 1 week of exposure was shown to reduce the rate of HA infection among household contacts from 5.8% in the untreated group to 1% with a protective efficacy of 79% (95% CI: 7%–95%).3
   In the study under consideration, all patients with HA infection were admitted to hospital. This may have limited the duration of exposure of family contacts, reducing the rate of disease in both the vaccine and the IG groups. However, in many parts of the world, most patients with acute viral hepatitis are not admitted to a hospital. The results of the current study may not be fully applicable in such a setting.
   The applicability of this study’s data and the utility of HA vaccine for post-exposure prophylaxis in the Indian setting may need consideration. It has been suggested that the epidemiology of HA infection in India is in the transition phase. This implies that improving standards of hygiene, especially in people of a higher socioeconomic group, have led to a reduced exposure to HAV infection in recent years. In population-based serological surveys conducted in urban and rural areas of Pune, during 1982, 1992 and 1998, it was shown that 69% (6–10 years), 53% (11–15 years) and 15% (16–25 years) of the population belonging to the higher socioeconomic group was anti-HAV negative in 1998. In contrast, 94%, 97% and 100%, respectively, of people with a lower socioeconomic group in these age groups had been exposed to HAV.4 Similar figures were reported in a study from Delhi, with HAV positivity rates of only 57% in subjects <35 years and 92% in those >35 years of age.5 In another multicentric study from India, the anti-HAV positivity rate ranged from 26% to 85%, with almost 50% of children in the age group of 1–5 years being susceptible.6 Thus, in recent years, a substantial pool of susceptible people has been generated. Because of a continuing circulation of HAV in our population, these people are at risk for HA outbreaks.7 Both daycare outbreaks8 and a large common source outbreak9 involving nearly 1100 subjects have recently been reported from Kottayam, Kerala. This suggests that the results of this study will find frequent application in India.
   However, notwithstanding the above evidence favouring transition in HA epidemiology, a vast majority of our population still belongs to the lower socioeconomic group. In a recent cross-sectional, community-based study from Delhi, only 26.2% of 2095 randomly selected families belonged to the high or upper middle socioeconomic groups.10 This limits the applicability of any post-exposure prophylaxis to a small percentage of our total population. In fact, in a larger study of anti-HAV seroprevalence done among 500 schoolchildren (age 10–17 years) from two government schools in Delhi, 97.2% of all children were anti-HAV positive with similar exposure rates of 98.6%, 94.8% and 98.3% in the age groups of 10–12, 13–14 and 15–17 years, respectively.11 In another study, these workers found high anti-HAV positivity rates in even younger schoolchildren, i.e. 86.4% and 91% in the age groups of 4–7 and 8–11 years , respectively.12
   Another group in which prevention of HA infection may be of importance is patients with chronic liver disease, in whom this infection is associated with a poor outcome. However, in India, adults with chronic liver disease are usually already immune to HA, with anti-HAV rates of 93%–97% in several studies.12,13
   Even if the HA vaccine is useful in the post-exposure setting, is its use practical in India? We must bear in mind that neither HA vaccine nor IG has been shown to be efficacious if given more than 2 weeks after exposure. Further, both these interventions are costly and thus should be used only if there is a reasonable expectation of benefit. In the current study, nearly 70% of contacts were either already immune or had evidence of co-primary infection by the time HA was identified in the index patient. The prophylactic measure was thus wasted in this large subpopulation of contacts. This wastage may be even higher in the Indian setting. Furthermore, with most HAV infections in India occurring in children, the index patients are likely to be either asymptomatic or to have anicteric disease,14 precluding their detection and thus the use of prophylactic vaccination of contacts. Even when index patients are icteric, a vast majority of them either do not reach medical services or undergo specific tests to differentiate HA from other causes of hepatitis such as hepatitis B or hepatitis E virus infection. Most often than not, by the time all these steps are completed, more than 2 weeks have passed since the onset of symptoms, rendering both IG and vaccine ineffective.
   In routine clinical practice in India, the source of infection in children with HA is infrequently identified. It is rare to encounter children with HA who give a history of another family member or school contact having recently been diagnosed as having HA. Thus, it is unlikely that many of these HA cases would have been prevented by the administration of HA vaccine for post-exposure prophylaxis, even if such a policy were in place and fully implemented. In fact, even in the West, a source of HA can be determined in only 43% of patients, with household contacts and daycare exposures accounting for only 12% and 2% of patients with HA, respectively.15 In most of these ‘unknown exposure’ cases, the infection is acquired from unrecognized HA infection among young children in the family. Post-exposure vaccination cannot be expected to be useful in this situation.
   The other situation where post-exposure prophylaxis using HA vaccine may be useful is during outbreaks of HA, especially in urban areas. Even there, the applicability in India may be limited since a specific diagnosis of the agent causing the outbreak is often delayed.
   It is likely that, in India, this study will be used by pharmaceutical interest groups to promote the use of HA vaccine among all family members, and school and neighbourhood contacts of patients with any form of viral hepatitis. Any attempts to do so must be thwarted by the medical profession. We must insist on ensuring that the vaccine is used for post-exposure prophylaxis only when the illness in an index patient has been proven to be due to HA, is of <2 weeks’ duration and when the contact has been shown to be non-immune to HAV. Otherwise, in the Indian setting of relatively unregulated medical practice, we will waste a lot of scarce resources.
   The greater role of HA vaccine will continue to be for pre-exposure prophylaxis in certain populations which may be at a higher risk of HA. Till now, the HA vaccine has been used on an individual basis. There is a need for studies on cost–benefit analysis in Indian population groups to better understand the effects of a universal HA vaccination policy. Also, urgent steps are needed to improve sanitation and provide clean water supplies, which are the most effective strategies known to reduce the transmission of several faeco–oral transmitted diseases including HA.

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