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Background: Hepatitis B is a major health concern in Africa. The vaccine against hepatitis B virus (HBV) was introduced into the Expanded Programme on Immunization (EPI) of Cameroon and Senegal in 2005, and of CAR (Central African Republic) in 2008. A cross-sectional study was conducted to assess HBV immunization coverage following the vaccine’s introduction into the EPI and factors associated with having been vaccinated. Methods: All hospitalized children, regardless of the reasons for their hospitalization, between 3 months and 6 years of age, for whom a blood test was scheduled during their stay and whose condition allowed for an additional 2 mL blood sample to be taken, and who provided the parent’s written consent were included. All children anti-HBs- and anti-HBc + were tested for HBsAg. Vaccination coverage was assessed in three different ways: immunization card, maternal recall and serologic anti-HBs profile. Results: 1783 children were enrolled between April 2009 and May 2010. An immunization card was only available for 24 % of the children. The median age was 21 months. Overall HBV immunization coverage based on immunization cards was 99 %, 49 % and 100 % in Cameroon, CAR and Senegal, respectively (p < 0,001). The immunization rate based on maternal recall was 91 %, 17 % and 88 % in Cameroon, CAR and Senegal, respectively (p < 0,001). According to serology (anti-HBs titer ≥ 10 mUI/mL and anti-HBc-), the coverage rate was 68 %, 13 % and 46 % in Cameroon, CAR and Senegal, respectively (p < 0,001). In Senegal and Cameroon, factors associated with having been vaccinated were: mother's higher education (OR = 2.2; 95 % CI [1.5-3.2]), no malnutrition (OR = 1.6; 95 % CI [1.1-2.2]), access to flushing toilets (OR = 1.6; 95 % CI [1.1-2.3]), and < 24 months old (OR = 2.1; 95 % CI [1.3-3.4] between 12 and 23 months and OR = 2.7; 95 % CI [1.6-4.4] < 12 months). The prevalence of HBV-infected children (HBsAg+) were 0.7 %, 5.1 %, and 0.2 % in Cameroon, CAR and Senegal, respectively (p < 0.001). Conclusions: Assessing immunization coverage based on immunization cards, maternal recall or administrative data could be usefully reinforced by epidemiological data combined with immunological profiles. Serology-based studies should be implemented regularly in African countries, as recommended by the WHO. Malnutrition, lack of maternal education and poverty are factors associated with vaccine non-compliance. The countries' vaccination programs should actively address these problems.
A cross-sectional study was conducted in five children’s hospitals: one hospital in Bangui (CAR), two in Yaoundé (Cameroon) and two in Dakar (Senegal). Both the Yaoundé and Dakar study sites included one pediatric hospital treating infants from families of impoverished socioeconomic status, and one general hospital serving a relatively well-off population. The Bangui site was a pediatric hospital serving children from families of all socioeconomic levels living in the city and its outskirts. Between April 2009 and May 2010, children aged 3 month to 6 years, hospitalized for any reason, with a blood sample prescribed during hospitalization, health conditions allowing an extended blood sample between 2 mL and 5 mL according to the age. Children were consecutively enrolled after their parents or legal guardians received an information notice and oral explanation in the local language and provided a written consent. This study was approved by the Senegal Health Research National Council, the National Ethics Committee of Cameroon and the Scientific Committee responsible for validation protocols and study results in Central African Republic. Data collected were: i) general characteristics (age, sex, weight), ii) clinical features (reasons for hospitalization, vaccination records on the immunization card), iii) socio-economic characteristics (place of residence, number of people in the household, mother’s education (higher level: at least primary education), personal transportation, electricity, running water, toilets type) and iv) serological data (anti-HBs antibodies, anti-HBc antibodies, HBsAg, HBeAg) and HBV DNA, when the child was HBsAg-positive. If the enrolled child’s immunization card was available, vaccination against HBV and dates of vaccination were recorded. Otherwise, the mother was asked about the child’s vaccination status. Complete vaccination was defined as having received all three injections according to the vaccination card in compliance with the WHO vaccination schedule (6, 10 and 14 weeks of age). Partial vaccination was defined as having received one or two doses according to the immunization card, regardless of the immunization schedule. Nutritional status was estimated separately for boys and girls by the Z-score, calculated on the weight for age, according to WHO standards for children between 3 and 60 months old, and to CDC standards for older children. Moderate or severe malnutrition was defined as a Z-score ≤ −2 SD [19–21]. All samples were tested for anti-HBc and quantified for anti-HBs by Enzyme ImmunoAssay (EIA) (DiaSorin Biomedica, Sallugia, Italy). The correlate of protection for HBV is an anti-HBs titer ≥10 mIU/mL [22, 23]. All children anti-HBs-negative and anti-HBc-positive were tested for HBsAg by automated EIA (AxSYM, Abbott laboratories, Chicago, USA). All HBsAg-positive children’s mothers were called by phone so that children could be retested free of charge six months later. Viral loads were measured by the Cobas AmpliPrep/Cobas TaqMan HBV assay, v2.0 (Roche Diagnostics, Meylan, France) at Saint-Louis Hospital. The limit of detection was 20 IU /mL. Except for viral load quantification, all laboratory tests were performed in each country. The children’s characteristics were described as medians and interquartile ranges (IQR) for continuous variables and percentages for discrete variables. For univariate and multivariate analysis, quantitative variables were expressed as dichotomous variables using either the median or a clinically relevant threshold. Univariate analysis was based on the Fisher’s exact test for discrete variables and by analysis of variance or the Kruskal-Wallis test for continuous variables. All variables associated with “having been vaccinated” in univariate analysis (p < 0.25) were included in a backward stepwise logistic regression model. A p value of ≤0.05 was considered statistically significant. Adequacy of the model was established through the Hosmer Lemeshow tests. Interactions between the variables found to be associated with “having been vaccinated” in the univariate analysis were tested using likelihood-ratio test. Our data on immunization coverage estimated by serological markers in children born one year after integration of vaccine into EPI (2005 in Cameroon and Senegal, and 2008 in CAR) were compared with data reported by WHO on immunization coverage of surviving infants between 2006 and 2009 [24–26]. Data were analyzed using STATA software version 12.0 (Stata Corporation, College Station, Texas). Using the only publication showing that it is possible to distinguish between the passive transfer of maternal anti-HBc and HBV exposure in children ≥12 months [27], we divided subjects between children younger than 12 months and those older than 12 months.
