What is the true burden of diphtheria, tetanus, pertussis and poliovirus in children aged 3–18 in Asia? A systematic literature review

Diphtheria transmission dynamics - Unveiling generation time and reproduction numbers from the 2022-2023 outbreak in Kano state, Nigeria

Background

Diphtheria, caused by Corynebacterium diphtheriae, remains a serious public health threat in areas with low vaccination coverage, despite global declines due to widespread immunization and improved clinical management. A major outbreak in Nigeria from 2022 to 2023 underscored the persistent risk in regions with inadequate vaccination. This study aims to assess the transmission dynamics of diphtheria in Kano State, the epicenter of the outbreak, by estimating key epidemiological parameters, including the generation time (GT), approximated in our study by serial interval, and effective reproduction number (Rₜ).

Methods

We analyzed diphtheria case-based data from Kano State, Nigeria, collected between August 18, 2022, and November 29, 2023. Generation time was approximated using serial intervals in confirmed cases within the same geographical areas. The effective reproduction number (Rₜ) was calculated using four methods: Maximum Likelihood Estimation (MLE), Exponential Growth (EG), Sequential Bayesian (SB), and Time-Dependent (TD), focusing on the period of maximum exponential growth. A sensitivity analysis was conducted to quantify the impact of uncertainties in the GT derived from our data on the estimation of Rₜ.

Results

Over the 469-day outbreak period, 13,899 diphtheria cases were reported, with complete data available for 9406 cases. The estimated mean generation time was 2.8 days (SD = 3.48 days), with 97% of cases having a GT of less than 21 days. The Rₜ estimates varied across methods, with the TD method producing the highest reproduction number of 2.21 during the peak growth period. Sensitivity analysis showed that Rₜ estimates increased with longer generation times. The models, except for the SB method, demonstrated a generally strong fit with the outbreak exponential growth period.

Conclusion

The ongoing diphtheria outbreak in Nigeria highlights the critical threat posed by declining vaccination coverage. This study provides valuable insights into the transmission dynamics of diphtheria during a prolonged and widespread outbreak, enhancing our understanding of disease spread in this context. While certain limitations may influence the interpretation of our estimates, the findings offer valuable information for future diphtheria outbreak preparedness and response in the African context.

A population-level analysis of armed conflict and diphtheria at the subnational level in the WHO African Region 2017-2024

BACKGROUND

Diphtheria has been re-emerging around the world at alarming rates, raising concerns about emergency preparedness, especially when global supplies of life-saving diphtheria antitoxin are insufficient. Outbreaks have occurred in areas with suboptimal coverage of the three-dose diphtheria tetanus and pertussis (DTP3) vaccine and regions experiencing conflict, but systematic studies assessing the association between these variables and the risk of diphtheria emergence are limited. This population-level study investigated the relationship between fatalities from armed conflict, childhood DTP3 vaccination coverage, and the presence of reported diphtheria cases in countries in the World Health Organization's (WHO) African region from 2017 to 2024.

METHODS

The analysis was conducted at a subnational geographic scale (I countries = 35, N subnational regions = 541). Data sources include DTP3 coverage from the Demographic Health Surveys (DHS), conflict-related fatalities from the Armed Conflict Location and Event Database (ACLED), and diphtheria cases from the WHO. We first assessed whether a history of fatalities from armed conflict is a predictor of childhood DTP3 coverage using mixed-effects beta regression. To assess the relationship between conflict and diphtheria emergence, we fit a crude logistic regression model to assess their overall association in the study period, as well as repeated measures mixed-effects models to estimate the relationship between time-varying rates of conflict-related fatalities and diphtheria status, adjusting for diphtheria vaccine coverage estimates.

RESULTS

Conflict and subsequent childhood DTP3 vaccine coverage were negatively associated (odds ratio [OR] = 0.93, 95% CI 0.88-0.98). Conflict is also a significant predictor of diphtheria presence, both in the crude (OR = 1.41, 95% CI 1.17-1.68) and best-fitting repeated measures model (OR = 30.30, 95% CI 23.30-39.39), though risk varied by location. The best-fit model also associated lower estimates of diphtheria risk in areas with high (> 80%) and low (< 25%) vaccine coverage, though this is possibly due to underreporting of the true burden of disease in low-resource settings.

CONCLUSIONS

This exploratory analysis indicates that conflict-related fatalities are potentially helpful indicators of subnational diphtheria risk in countries in the WHO African region from 2017 to 2024. Further, it may be especially useful in cases where estimates of population-level diphtheria immunity are limited.

Influence of Hematocrit and Storage Temperature on the Stability of Dried Blood Samples in Serological Analyses of Tetanus, Diphtheria, and Pertussis

BACKGROUND

Dried blood spots (DBSs) enable the study of serological markers of various pathogens without the need to obtain serum/plasma through venipuncture.

METHODS

Sixty-four blood samples were prepared on Whatman™ 903 cards using specimens obtained by venipuncture to study the detection of serological markers of diphtheria, tetanus, and pertussis in DBSs, and their stability 4 months post-collection. An automated chemiluminescent immunoassay was used to investigate diphtheria, tetanus, and pertussis IgG levels from both DBSs and plasma samples.

RESULTS

An optimal cut-off value for DBSs was calculated to improve the performance of diphtheria and tetanus serological markers in DBSs, achieving high sensitivity (95% and 98%, respectively) and specificity (91.7% and 92.3%, respectively). No protection against pertussis was found in the population studied. The correlation observed between the plasma and the DBSs processed after sample collection was high (0.967-0.970) for all antibodies studied except pertussis (0.753), both considering hematocrit before sample elution or not. The correlation between DBSs and plasma for diphtheria and tetanus remained strong following a 4-month delay in DBS processing at 4 °C (0.925-0.964) and -20 °C (0.924-0.966), with only a minor decrease observed for diphtheria at room temperature (0.889), while maintaining a strong correlation for tetanus (0.960). For pertussis, the correlation between DBSs and plasma was drastically reduced after delaying its processing for 4 months at any temperature.

CONCLUSIONS

To summarize, hematocrit levels within the normal range do not affect the processing of DBSs in the study of serological markers of diphtheria, tetanus, and pertussis. The DBS stability for serological diagnosis of diphtheria and tetanus is adequate when samples are stored at -20 °C for a period of 4 months. The pertussis serological marker does not appear to remain stable after 4 months, even when the DBS is stored frozen at -20 °C.

The Improvement of Adaptive Immune Responses towards COVID-19 Following Diphtheria-Tetanus-Pertussis and SARS-CoV-2 Vaccinations in Indonesian Children: Exploring the Roles of Heterologous Immunity

BACKGROUND

Routine childhood vaccination, e.g., for diphtheria, tetanus, and pertussis (DTP), might provide additional protection against SARS-CoV-2 infection. This concept of heterologous immunity was explored in healthy children receiving both DTP and inactivated SARS-CoV-2 vaccines.

METHODS

A cross-sectional study was performed on 154 healthy children aged 6-8 years old in Jakarta, Indonesia. Their vaccination status for the DTP (including a diphtheria-tetanus booster vaccine at 5 years old) and CoronaVac (from 6 years old) vaccines were recorded. Peripheral blood samples were collected from all participants, in which anti-diphtheria toxoid IgG and anti-SARS-CoV-2 S-RBD antibodies and T cell-derived IFN-γ were measured.

RESULTS

The study participants with complete DTP vaccination had significantly higher titers of anti-diphtheria toxoid IgG than the ones without (median = 0.9349 versus 0.2113 IU/mL; p < 0.0001). Upon stratification based on DTP and CoronaVac vaccination statuses, the participants with complete DTP and CoronaVac vaccinations had the highest titer of anti-SARS-CoV-2 S-RBD antibodies (median = 1196 U/mL) and the highest concentration of SARS-CoV-2-specific T cell-derived IFN-γ (median = 560.9 mIU/mL) among all the groups.

CONCLUSIONS

Healthy children aged 6-8 years old with complete DTP and CoronaVac vaccinations exhibited stronger SARS-CoV-2-specific T cell immune responses. This might suggest an additional benefit of routine childhood vaccination in generating protection against novel pathogens, presumably via heterologous immunity.

Assessing the impact of booster vaccination on diphtheria transmission: Mathematical modeling and risk zone mapping

The COVID-19 pandemic caused significant disruptions in the healthcare system, affecting vaccinations and the management of diphtheria cases. As a consequence of these disruptions, numerous countries have experienced a resurgence or an increase in diphtheria cases. West Java province in Indonesia is identified as one of the high-risk areas for diphtheria, experiencing an upward trend in cases from 2021 to 2023. To analyze the situation, we developed an SIR model, which integrated DPT and booster vaccinations to determine the basic reproduction number, an essential parameter for infectious diseases. Through spatial analysis of geo-referenced data, we identified hotspots and explained diffusion in diphtheria case clusters. The calculation of R0 resulted in an R0 = 1.17, indicating the potential for a diphtheria outbreak in West Java. To control the increasing cases, one possible approach is to raise the booster vaccination coverage from the current 64.84% to 75.15%, as suggested by simulation results. Furthermore, the spatial analysis revealed that hot spot clusters were present in the western, central, and southern regions, posing a high risk not only in densely populated areas but also in rural regions. The diffusion pattern of diphtheria clusters displayed an expansion-contagious pattern. Understanding the rising trend of diphtheria cases and their geographic distribution can offer crucial insights for government and health authorities to manage the number of diphtheria cases and make informed decisions regarding the best prevention and intervention strategies.

Safety and immunogenicity of an indigenously developed tetanus toxoid, diphtheria toxoid, and acellular pertussis vaccine (Tdap) in adults, adolescents, and children in India

BACKGROUND

This study assessed safety and immunogenicity of Serum Institute of India Pvt Ltd (SIIPL)'s tetanus toxoid (TT), diphtheria toxoid (DT), and acellular pertussis booster vaccine (Tdap).

RESEARCH DESIGN AND METHODS

In this Phase II/III, multicenter, randomized, active-controlled, open-label study, 1500 healthy individuals, aged 4-65 years, were randomized to receive a single dose of SIIPL Tdap or comparator Tdap vaccine (Boostrix®; GlaxoSmithKlines, India). Adverse events (AEs) during initial 30 minutes, 7-day, 30-day post-vaccination were assessed. Blood samples were taken before and 30 days post-vaccination for immunogenicity assessment.

RESULTS

No significant differences in incidence of local and systemic solicited AEs were observed between the two groups; no vaccine-related serious AEs were reported. SIIPL Tdap was non-inferior to comparator Tdap in achieving booster responses to TT and DT in 75.2% and 70.8% of the participants, respectively, and to pertussis toxoid (PT), pertactin (PRN), and filamentous hemagglutinin (FHA) in 94.3%, 92.6%, and 95.0% of the participants, respectively. Anti-PT, anti-PRN, and anti-FHA antibody geometric mean titers in both the groups, were significantly higher post-vaccination compared to pre-vaccination.

CONCLUSIONS

Booster vaccination with SIIPL Tdap was non-inferior to comparator Tdap with respect to immunogenicity against tetanus, diphtheria, and pertussis and was well tolerated.

A combined DTaP-IPV vaccine (Tetraxim®/Tetravac®) used as school-entry booster: a review of more than 20 years of clinical and post-marketing experience

INTRODUCTION

Routine infant primary series and toddler booster vaccination are associated with waning of antibody levels over time, which can lead to an increased incidence of vaccine-preventable diseases. A diphtheria-tetanus-pertussis (DTP) booster vaccination at school-entry (aged 4-7 years) allows continued protection against these diseases and is included in many national immunization programs.

AREAS COVERED

The available immunogenicity and safety data from 6 clinical studies of a diphtheria-tetanus-acellular pertussis-inactivated poliovirus vaccine (DTaP-IPV [Tetraxim®]) used as a school-entry booster vaccination were identified using a PubMed search or on file at Sanofi. The studies spanned a 15-year period (1995-2010) and were performed in different populations using different study designs, so all data were reviewed descriptively (no meta-analyses were conducted). Additionally, post-marketing experience was reviewed.

EXPERT OPINION

Each vaccine antigen is highly immunogenic, and the safety profile of the vaccine is satisfactory. Post-marketing evaluations have shown the effectiveness of a school-age booster, particularly against increased pertussis disease incidence around the time of school entry and the associated risk of spreading the disease through contact with younger vulnerable infants. School-entry provides an ideal opportunity to implement DTaP-IPV vaccination to close the gap between waning immunity from the previous infant/toddler vaccination and future adolescent vaccination.