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Seroprotection at different levels of the health care system after routine vaccination with DTPw-HepB-Hib in Lao PDR.

BACKGROUND
Lao PDR continues to sustain a considerable burden of vaccine preventable diseases because of incomplete vaccine coverage and weak vaccine responses. We have assessed seroconversion after routine vaccination with DTPw-HepB-Hib to capture weaknesses of vaccine management at the different levels of the health care system.


METHODS
1151 children (8-28 months) with three documented doses of the pentavalent vaccine delivered at Central hospitals in Vientiane and the Provincial hospital, 3 district hospitals and 10 health centers in Bolikhamxay province were enrolled. Socio-demographic information was collected with a standardized questionnaire. Serum samples were analysed for antibodies against each of the vaccine components and bivariate and multivariable analyses were performed to identify risk factors for low vaccine responses.


RESULTS
Seroprotection rates at the provincial, district and health center level were as high as in Central hospitals but seroprotection rates in areas covered by remote health centers (>60 min from district hospital) were significantly lower. Protective levels also rapidly decreased with age at sampling. Seroprotection rates in Bolikhamxay against the different components reached 70%-77% and were up to 20% higher than in previous studies in the same region: 18.8% more children received the hepatitis B vaccine birth dose and the HBV infection rate was 4 times lower.


CONCLUSION
Vaccine immunogenicity has dramatically improved in a central province, likely thanks to training and investment in the cold chain. Nevertheless there remains a need to focus on the "last mile" in remote areas were most children are vaccinated through outreach activities.