Diagnostic accuracy of dried blood spots for serology of vaccine-preventable diseases: a systematic review

Designing a National Rapid Vaccine Coverage Survey in low-resource settings: Experiences from the Democratic Republic of the Congo 2018-2023

In the Democratic Republic of the Congo (DRC), estimating vaccine coverage (VC) has traditionally relied on large-scale surveys such as the Demographic and Health Surveys (DHS) and the Multiple Indicator Cluster Surveys (MICS). However, these surveys are infrequent, costly, and lack the granularity needed for decision-making at the health district or zone (HZ) level. This paper describes the development by the Kinshasa School of Public Health (KSPH), and technical partners of a Vaccine Coverage Survey (KSPH VCS), adapted from the World Health Organization (WHO) guidelines, which aims to provides timely, cost-effective, and representative estimates of VC at the HZ level. The KSPH VCS adopted a cross-sectional design and a multi-stage sampling approach to sample households at the HZ level. It uses Health Area as cluster in spite of Enumeration Area, and extends the eligibility age range from 12 -23 months to 6-23 months. The sample size for each HZ was calculated using vaccine coverage provided in MICS-2018. It integrates assessments of barriers and enablers to vaccination. Since 2023, it has included malaria indicators. Since its inception in 2018, it has expanded nationwide, covering all 26 provinces of the DRC by 2022. Findings from the KSPH VCS provides estimates at the HZ level that could be combined to provincial and national estimates. Results have been instrumental in evaluating national immunization strategies, including the Mashako Plan and informing Presidential Forums on immunization. They have informed resource allocation, operational planning, and policy decisions at both national and provincial levels as they provided granularity needed for operational decision-making at the HZ level. Its results have also contributed to global immunization estimates, including the WHO/UNICEF Estimates of National Immunization Coverage (WUENIC). The KSPH VCS demonstrates the feasibility of a locally led, cost-effective, and adaptable VC survey in a low-resource setting. Its success highlights the potential for similar methodologies to be implemented in other low- and middle-income countries seeking to improve immunization monitoring and health system performance.

Weighted prevalence and associated risk factors of hepatitis E virus antibodies among pregnant women in rural Burkina Faso using dried blood spot samples

AIM

To estimate the weighted prevalence of hepatitis E virus (HEV) antibodies and risk factors among pregnant women in Burkina Faso and to evaluate the efficiency of dried blood spots (DBS) in detecting HEV antibodies.

METHODS

We first evaluated the efficiency of DBS detecting HEV antibodies by comparing 62 DBS with matched serum samples using recomWell IgG and IgM kits (Mikrogen Diagnostik). Anti-HEV immunoglobulin G (IgG) and immunoglobulin M (IgM) were identified in 491 DBS samples collected from pregnant women in Burkina Faso using recomWell kits. HEV RNA was tested using HEV nested polymerase chain reaction among HEV-antibodies positive. The survey-weighted method was applied for prevalence calculations and risk factors analysis.

RESULTS

The detection of anti-HEV IgG and anti-HEV IgM in DBS samples revealed a sensitivity of 96.7% and 76.7% and a specificity of 100% and 93.8% compared to serum samples, respectively. Among 491 pregnant women tested, the weighted prevalence of anti-HEV IgG was 18.6%, and anti-HEV IgM was 2.5%, with no HEV RNA detected. A significant age-related increase was observed in the prevalence of anti-HEV IgG (p < 0.001), while no significant was found for anti-HEV IgM-positivity (p = 0.1451). Multiparity was significantly associated with anti-HEV IgG-positivity, while women aged 25-34 years were at higher risk of anti-HEV IgM-positivity.

CONCLUSION

This study revealed that DBS is a reliable alternative for HEV seroepidemiological studies, especially in resource-limited settings, although further investigation is needed for anti-HEV IgM detection. The weighted prevalence of anti-HEV IgG was 18.6% and anti-HEV IgM was 2.5%, highlighting the ongoing burden of HEV infection, particularly in high-risk groups like pregnant women in rural Burkina Faso.

Exploring Natural Immune Responses to Shigella Exposure Using Multiplex Bead Assays on Dried Blood Spots in High-Burden Countries: Protocol From a Multisite Diarrhea Surveillance Study

Background

Molecular diagnostics on human fecal samples have identified a larger burden of shigellosis than previously appreciated by culture. Evidence of fold changes in immunoglobulin G (IgG) to conserved and type-specific Shigella antigens could be used to validate the molecular assignment of type-specific Shigella as the etiology of acute diarrhea and support polymerase chain reaction (PCR)-based microbiologic end points for vaccine trials.

Methods

We will test dried blood spots collected at enrollment and 4 weeks later using bead-based immunoassays for IgG to invasion plasmid antigen B and type-specific lipopolysaccharide O-antigen for Shigella flexneri 1b, 2a, 3a, and 6 and Shigella sonnei in Shigella-positive cases and age-, site-, and season-matched test-negative controls from all sites in the Enterics for Global Health (EFGH) Shigella surveillance study. Fold antibody responses will be compared between culture-positive, culture-negative but PCR-attributable, and PCR-positive but not attributable cases and test-negative controls. Age- and site-specific seroprevalence distributions will be identified, and the association between baseline antibodies and Shigella attribution will be estimated.

Conclusions

The integration of these assays into the EFGH study will help support PCR-based attribution of acute diarrhea to type-specific Shigella, describe the baseline seroprevalence of conserved and type-specific Shigella antibodies, and support correlates of protection for immunity to Shigella diarrhea. These insights can help support the development and evaluation of Shigella vaccine candidates.

Effect of the Hematocrit and Storage Temperature of Dried Blood Samples in the Serological Study of Mumps, Measles and Rubella

Dried blood spots (DBSs) are an economical and convenient alternative to serum/plasma, which allow for the serological and molecular study of different pathogens. Sixty-four blood samples were collected by venipuncture and spotted onto Whatman™ 903 cards to evaluate the utility of DBSs and the effect of the storage temperature for 120 days after sample collection to carry out serological diagnosis. Mumps, measles and rubella IgG were investigated from DBSs and plasma using an automated chemiluminescent immunoassay. Using a calculated optimal cut-off value, the serological evaluation of mumps, measles and rubella using DBSs achieved high sensitivity (100%, 100% and 82.5%, respectively) and specificity (100%, 87.5% and 100%, respectively). The correlation observed between the plasma and the DBSs processed after sample collection was high (0.914-0.953) for all antibodies studied, both considering hematocrit before sample elution or not. For the different storage conditions, the correlation with plasma was high at 4 °C (0.889-0.925) and at -20 °C (0.878-0.951) but lower at room temperature (0.762-0.872). Measles IgG results were more affected than other markers when DBSs were stored at any temperature for 120 days. To summarize, hematocrit does not affect the processing of DBSs in the study of serological markers of mumps, measles and rubella. DBS stability for serological diagnosis of mumps and rubella is adequate when samples are stored at -20 °C or 4 °C, but not at room temperature, for a period of 4 months.

Serology as a Tool to Assess Infectious Disease Landscapes and Guide Public Health Policy

Understanding the local burden and epidemiology of infectious diseases is crucial to guide public health policy and prioritize interventions. Typically, infectious disease surveillance relies on capturing clinical cases within a healthcare system, classifying cases by etiology and enumerating cases over a period of time. Disease burden is often then extrapolated to the general population. Serology (i.e., examining serum for the presence of pathogen-specific antibodies) has long been used to inform about individuals past exposure and immunity to specific pathogens. However, it has been underutilized as a tool to evaluate the infectious disease burden landscape at the population level and guide public health decisions. In this review, we outline how serology provides a powerful tool to complement case-based surveillance for determining disease burden and epidemiology of infectious diseases, highlighting its benefits and limitations. We describe the current serology-based technologies and illustrate their use with examples from both the pre- and post- COVID-19-pandemic context. In particular, we review the challenges to and opportunities in implementing serological surveillance in low- and middle-income countries (LMICs), which bear the brunt of the global infectious disease burden. Finally, we discuss the relevance of serology data for public health decision-making and describe scenarios in which this data could be used, either independently or in conjunction with case-based surveillance. We conclude that public health systems would greatly benefit from the inclusion of serology to supplement and strengthen existing case-based infectious disease surveillance strategies.