Standardization of the methods and reference materials used to assess virus content in varicella vaccines

BACKGROUND: In Korea, every vaccine lot is tested by the National Center for Lot Release (NCLR) in accordance with the national lot release procedures to ensure the safety and efficacy of vaccines. These quality tests examine the virus content in varicella vaccines via plaque assays (either the agar overlay method [AOM] or plaque staining method [PSM]), according to the procedures suggested by the Korean Reference Material for the Varicella Vaccine (KRMVV) or the manufacturer’s standard in-house protocol. AIM: To standardize the virus content tests, viral titers in the KRMVV were measured using the PSM at four participating laboratories in a collaborative study. With the aim of developing a standardized method using the KRMVV as a positive control, we compared the ability of the two test methods, AOM and PSM, to accurately and reproducibly determine the virus content of two commercial varicella vaccines. RESULTS: The results showed that the standardized method (PSM) was more suitable for quality control analysis of the varicella vaccine. CONCLUSION: Use of a standardized method (PSM) according to the Korean reference material will improve the reliability and objectivity of lot release testing

Varicella-zoster virus seroprevalence in children and adolescents in the pre-varicella vaccine era, Germany

Background: In 2004, universal childhood varicella vaccination was introduced in Germany. We aimed to determine the age-specific prevalence of anti-varicella zoster virus (VZV) IgG-antibodies among children in the pre-varicella vaccine era in Germany, to identify factors associated with VZV seropositivity, and to assess the suitability of a commercially available ELISA for VZV seroepidemiological studies by comparing it with an in-house fluorescent antibody to membrane antigen test (FAMA) as the gold standard. Methods: Serum samples of 13,433 children and adolescents aged 1–17 years included in the population-based German Health Interview and Examination Survey for Children and Adolescents (KiGGS; conducted 2003–2006) were tested for anti-VZV IgG by ELISA. All samples with equivocal ELISA results and a random selection of ELISA-negative and -positive samples were tested by FAMA. Statistical analyses were conducted using a weighting factor adjusting the study population to the total population in Germany. Seroprevalences were calculated as percentages (%) with a 95% confidence interval (CI). Odds ratios (OR) were computed by multivariate logistic regression to determine the association between socio-demographic factors and VZV seropositivity. Results: The VZV seropositivity rate was 80.3% (95% CI: 79.3–81.3) in varicella-unvaccinated children and adolescents. VZV seropositivity rates differed significantly between age groups up to age 6 years, but not by gender. Of 118 retested serum samples with an equivocal ELISA result, 45.8% were FAMA-positive. The proportion of samples tested as false-negative in by ELISA varied by age group: 2.6% in children aged 1–6 and 9% in children aged 7–17 years. Multivariate analyses showed that age, having older siblings, and early daycare start were associated with seropositivity in preschoolers; migration background reduced the chance of VZV seropositivity in schoolchildren (OR: 0.65; 0.43–0.99) and adolescents (OR: 0.62; 0.4–0.97). Conclusion: In the pre-varicella vaccine era, most children in Germany contracted varicella by age six. Schoolchildren with a migration background and children without siblings have an increased risk of being VZV seronegative and should be targeted for catch-up vaccination, if they have no history of chickenpox. ELISAs are suitable for use in population-level serosurveys on VZV, but samples with equivocal ELISA results should be retested by FAMA

Molecular markers and the management of tropical trees: The case of indigenous fruits

Millions of people in the tropics benefit from the harvest, cultivation and consumption of indigenous fruit trees (IFTs). Knowledge concerning the structuring of genetic variation within these species is crucial for sustainable use and conservation, but the availability of such information has been limited. By reference to case study species that are currently the subject of active domestication initiatives, in this essay we provide guidance for the suitable application of molecular marker methods for characterising IFTs. We discuss three particular areas where molecular markers are able to provide unique insights for further promotion activities: (i) in understanding the past domestication of taxa, (ii) in determining effective population sizes; and (iii) in assessing the value of a decentralised approach for future domestication. Despite the potential utility of molecular markers, a disjunction between assessment and practical application is evident, which reflects a lack of integration of laboratory research with other species promotion activities. Greater emphasis is required on team-based research and partnerships, more work should be undertaken in agricultural landscapes, and further research on mating systems and gene flow are crucial. Our essay provides a model for molecular marker studies on other trees that are important to rural communities in the tropics.Ramni Jamnadass, Andrew Lowe and Ian K Dawso