10 year assessment of infant hepatitis B vaccination program, in the Loyalty Islands (New Caledonia)
Introduction
New Caledonia is an overseas territory, part of the French national community (special statute resulting from the Noumea Agreement, 1998). According to the 1996 census, its total population is 196.836 inhabitants distributed in three administrative provinces: 134.546 (68.3%) in the Southern Province, 41.413 (21.0%) in the Northern Province and 20.877 (10.7%) in the Province of the Loyalty Islands (including the three islands of Ouvea, Lifou and Mare). It is a young population: 31% are less than 15 years old, and whose principal ethnic groups are as follows: Melanesian (44.1%), European (34.1%) and Wallisian (9%). The birth-rate was 21.3 per thousand in 1998, and the average annual number of live births is 4375 (period 1990–1998) [1].
Although rare and of limited size, some studies show that the prevalence of hepatitis B virus (HBV) infection is high in New Caledonia, particularly in the Oceanian communities: the 1998 and 1999 monitoring of military recruits found that 6.6% were HBV chronic carriers [2]. Among pregnant women, the rate of carriage was 5.1% in 1982 [3] and 3.3% in 1996–1998 [4]. HBV acute infection may result in chronic carriage of the virus; this situation is much more frequent (up to 40%) when infection occurs early in the life [5]. In approximately 25% of the cases, the long term evolution leads to severe complications such as cirrhosis and liver cancer.
Taking into account these elements, HBV vaccination has become mandatory for all new-borns in New Caledonia since 1990, at the age of 2 months or at birth in case of maternal infection (Deliberation of the Territorial Parliament, 15 November 1989).
More than 10 years after the implementation of this policy, it was important to evaluate the current rate of vaccine coverage, among the 8–11 years old preadolescents. As these children will soon reach the second risk period of their life regarding HBV contamination, especially by sexual exposure, their residual level of protection has to be evaluated and the need of a booster injection examined.
In order to get some answers, a serological survey was performed from September–November 2001, among the school children of the Loyalty Islands, born in 1990 and 1991. The goals were to evaluate the frequency of the different HBV markers profiles, to measure the humoral immunity by anti-HBs antibody titration and to assess the current rate of HBV contamination in this age group. This last point could be evaluated accurately by comparison to recent data collected from 1997 and 1998 campaigns, carried out for a catch-up vaccine program in children of the Loyalty Islands, born before 1990. These results are also presented further.
Section snippets
Population enrolled
The 2001 study included 593 primary school children, born in 1990 or 1991, of which 287 live in Mare, 168 in Lifou and 138 in Ouvea. Inclusion of the children in the study needed the written consent of parents. For all children a blood sample was taken, and basic demographic and health information was obtained in their health record, collected on the previous days by their teachers. The following data was recorded.
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Identity: name, first name, sex, date of birth, school.
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Initial vaccine schedule
Population features
The 2001 study recruited 593 children, of which 53% were girls; the mean age was 10.6 years (8.4–11.8). Of them, 553 (93%), had received a complete HBV immunisation, using Gen Hevac B® in 99% of the cases. The Engerix® vaccine was occasionally used for booster shots in 1997. The three injections schedule (M0–M1–M6) was applied for 74% of the children, usually starting by the age of 2 or 3 months, together with the other vaccinations of early childhood. The four injections schedule
Representativity of the investigated patients
On the islands of Mare and Ouvea, all the children in primary school highest levels (CM1 and CM2) were checked for inclusion in the study, on Lifou island only the schools of the Northern sector (medical district of Chepenehe) were requested. From the 789 children solicited, 593 (75%) were included in the study. The rates of participation ranged from 54% in Ouvea, to 95% in Northern Lifou. Thus, the children who were absent from the school on the day of sampling and those who were not able to
Conclusion
With a vaccination coverage of 93% among preadolescents of the Loyalty Islands, it seems obvious that the mandatory and universal hepatitis B vaccination in new-borns implemented in 1989, is widely accepted by the population and practised. Nearly 89% of the children aged 9–11 years are protected against HBV infection and the prevalence of anti-HBc antibody shows a dramatic decrease, when compared with the cohorts of children born before 1989, investigated in 1997 and 1998. However, it is
Acknowledgements
This investigation was supported by the Government of New Caledonia. Thanks to Dr. Yves Perroy from the Loyalty Islands, Department Of Health, and all the medical staff of the provincial dispensaries who ensured the collection of blood samples and information.
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All French language references, except [1] and [4] have an English abstract.