Low and disparate seroprotection after pentavalent childhood vaccination in the Lao People's Democratic Republic: a cross-sectional study.

OBJECTIVE: In Lao People's Democratic Republic, the high burden of vaccine-preventable diseases is thought to be mainly due to low vaccine coverage. We investigated the seroprotective response against diphtheria-tetanus-whole cell pertussis-hepatitis B-Haemophilus influenzae type b (DTPw-HepB-Hib) vaccine in children. METHODS: Serum was collected from 1131 children aged 9 to 50 months and their mothers in a cross-sectional study between December 2013 and July 2014. All children had records of three injections of the DTPw-HepB-Hib vaccine. Serum was analysed for hepatitis B surface antigen (HBsAg), anti-HBsAg (anti-HBs), anti-hepatitis B virus core antigen (anti-HBc), anti-diphtheria and anti-tetanus antibodies. Stool samples were collected for detection of parasites. Demographic and nutritional information were also obtained. RESULTS: Protective levels of anti-HBs antibodies were found in 394 (37.9%) of 1039 children; 529 (55.7%) of 950 and 809 (85.2%) of 950 children were seroprotected against diphtheria and tetanus. Time since vaccination, age, home birth and malnutrition only partially explained the poor vaccine responses. Overall, 81 (7.8%) of 1039 children and 445 (40.3%) of 1105 of mothers were anti-HBc positive. Ten (1.0%) of 1039 of the children and 77 (7.0%) of 1105 of the mothers were HBsAg carriers. CONCLUSIONS: After a full documented course of vaccination, seroprotective rates were unusually low and disparate against components of the pentavalent vaccine. These can only partially be explained by the negative predictors identified. Although many children had been infected, only few were chronic carriers of HBsAg. Our study demonstrates an urgent need to monitor the serologic response to vaccination, particularly in resource-poor countries.

High prevalence of mumps in Lao People's Democratic Republic.

In the Lao People's Democratic Republic (PDR), mumps is not a notifiable disease and mumps vaccine is currently not included in the routine childhood immunization programme. In order to assess the burden of disease, we investigated the seroprevalence of mumps-specific IgG antibodies across four provinces. In addition, we genetically characterized mumps viruses from the past 3 years from several outbreaks and single cases. Blood and/or throat swabs from suspected cases were investigated for specific IgM antibodies or viral RNA. Mumps cases occurred between March and November in 2011-2013 and 5- to 15-year-olds were most affected. Four sequences from an outbreak in the north of Lao PDR in 2011 were identical and belonged to genotype G. Eight sequences from two outbreaks and two individual cases from 2012 and 2013 belonged to genotype J. In addition, sera collected from 2379 healthy infants and school pupils aged between 9 months and 19 years and from pregnant women aged between 16 and 46 years were investigated for mumps-specific IgG. Overall, 58.2% were positive, 39.5% were negative and the remaining 2.3% were equivocal. The seropositivity increased with age, with the lowest percentage found in <1-year-old infants (9.1%) and the highest in the cohort of pregnant women (69.2%). More female subjects than male subjects were seropositive (60.4 vs. 54.9%). There were some differences between the locations. Mumps should be a notifiable disease in Lao PDR in order to get more accurate case numbers and cost estimates for public health-care, and vaccination of children and high-risk groups should be considered.

Occult hepatitis B infections among blood donors in Lao PDR.

BACKGROUND AND OBJECTIVES: In Lao People's Democratic Republic, hepatitis B virus is highly endemic. However, blood donations are only screened for HBsAg, leaving a risk of transmission by HBsAg-negative occult infected donors. Here, we characterized first-time blood donors to assess prevalence of hepatitis B virus infections and occult infected donors. MATERIALS AND METHODS: Sera were screened for HBsAg, HBeAg and anti-HBs, anti-HBc and anti-HBe antibodies. Occult HBV infections (OBIs) were assessed in HBsAg-negative sera by PCR, and sera of HBsAg positive and occult infected donors were phylogenetically characterized. RESULTS: 9·6% of the donors were HBsAg positive, and 45.5% were positive for at least one of the hepatitis B virus serum markers. More than 40% HBsAg carriers were HBeAg positive, with HBeAg seroconversion occurring around 30 years of age. Furthermore, 10·9% of HBsAg-negative, anti-HBc and/or anti-HBs-positive donors were occult infected with hepatitis B virus. Thus, at least 3·9% of blood donations would potentially be unsafe, but hepatitis B virus DNA copy numbers greatly varied between donors. CONCLUSION: In Lao People's Democratic Republic, a sizable proportion of HBsAg-negative and anti-HBc antibody-positive blood donations are potentially DNA positive and infective for hepatitis B.

High genetic diversity including potential new subtypes of hepatitis C virus genotype 6 in Lao People's Democratic Republic.

Sera from 105 anti-HCV-positive first-time blood donors collected in 2004, 2005 and 2008 in different provinces in Laos were investigated by PCR. Forty-five samples were positive for HCV (42.86%); two belonged to subtype 1b (2/45, 4.4%) and all others to genotype 6 (43/45, 95.6%), including subtypes 6b, 6h, 6k, 6l, 6n and 6q. Three groups of sequences were not clearly attributable to any genotype 6 subtype, two of which may be regarded as candidates for new subtypes of genotype 6. Two samples were mixed infected with different subtypes or clusters of genotype 6 viruses.