Immunity against diphtheria among children aged 5-17 years in India, 2017-18: a cross-sectional, population-based serosurvey

Mapping anti-diphtheria toxin antibody: a systematic review and meta-analysis with multi-level meta-regression

Diphtheria is a reemerging vaccine-preventable infection of public health concern. Pooled estimates of serum IgG anti-diphtheria antibody levels can assist in estimating the susceptible population. The objective was to estimate pooled estimate of protective IgG anti-diphtheria antibodies in population globally. We searched three databases until May 2023. We included studies reporting serum anti-diphtheria antibody titre > 0.1 IU/ml as seroprotection. NHLBI checklist was used for quality assessment. Heterogeneity was explored and resolved by statistical methods. 1720 articles were retrieved out of which 51 articles were included. The pooled seropositivity rate against diphtheria was 57%. After removal of two influential outlier studies, pooled seropositivity became 51%. The meta-regression results for age depicted that seroprevalence significantly decreased with increasing age. Subgroup analysis done on basis of geographical distribution significantly reduced heterogeneity and revealed that the Western Pacific region and African regions had lower seroprotectivity compared to other regions. Subgrouping done based on year of sample collection revealed seroprotection was lower (55.63%) between 1986 and 2005 which increased to 67.11% between 2006 and 2015 and again dropped to 45.75% between 2016 and 2023. We concluded that after 2015, the disease has reemerged globally, with seroprotection level below 50% (45.75%) and overall only half of the population being seroprotected against diphtheria. So, there is a need for reinforcement of immunity against diphtheria (supplementary vaccination) after screening for antibody titre. PROSPERO registration number CRD42023458131.

Waning rate of immunity and duration of protective immunity against diphtheria toxoid as a function of age and number of doses: Systematic review and quantitative data analysis

Although the burden of diphtheria has declined greatly since the introduction of vaccines, sporadic outbreaks continue to be reported. WHO recommends booster doses after a primary series, but questions remain about the optimal interval between these doses. We conducted a systematic review and quantitative data analysis to quantify the duration of protective immunity after different numbers of doses. Fifteen cross-sectional seroprevalence studies provided data on geometric mean concentration (GMC). Single-year age-stratified GMCs were analyzed using a mixed-effect linear regression model with a random intercept incorporating the between-country variability. GMC was estimated to decline to 0.1 IU/ml in 2.5 years (95% CI: 0.9-4.0), 10.3 years (95% CI: 7.1-13.6), and 25.1 years (95% CI: 7.6-42.6) after receiving three, four and five doses, respectively. The results drawn from cross-sectional data collected in countries with different epidemiologies, vaccines, and schedules had several limitations. However, these analyses contribute to the discussion of optimal timing between booster doses of diphtheria toxoid-containing vaccine.

The evaluation of anti-diphtheria toxoid antibodies in healthy population in Kon Tum, Vietnam: a population-based study

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The risk of diphtheria remains high in Kon Tum given the low seroprevalence.

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One third of community in Kon Tum have no protective antibodies to diphtheria.

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The antibodies from previous childhood vaccination gradually wane over time.

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A booster dose (5-7 years) is recommended for adolescents and adults in Vietnam.

Background

Despite diphtheria immunization are to apply an effective primary immunization in childhood and to maintain immunity throughout life. Cases of diphtheria have been reported in Viet Nam in recent years. The aim of this study was to evaluate the seroprevalence of IgG antibodies to diphtheria toxoid among healthy person population in Kon Tum, Viet Nam.

Methods

Blood samples were obtained from 2225 healthy persons aged 2-98 years collected in 2019 and 2020. Samples were tested for diphtheria toxoid antibodies by commercial Anti-Diphtheria Toxoid IgG Enzyme-Linked Immunosorbent Assay (ELISA).

Results

An antibody level of <0.01 IU/mL (susceptibility) was found in 802 (36.0%) of the 2225 subjects, 136 (6.1%) had antibody levels of 0.01–0.099 IU/mL (basic protection), and 1287 (57.8%) had antibody levels ≥0.1 IU/mL (full protection). The full protection level increased significantly in persons aged above 60 years with antibody levels of 70.6%. No significant difference in seroprotection prevalence was found according to gender, ethnicity, residence, education and occupation. The results also demonstrated that people with vaccination against diphtheria during past 10 years were found to have a high immunity (83.8%) compared to 54.8% (OR: 4.7; 95%CI: 3.8-6.5) and 60.7% (OR: 3.8; 95%CI: 2.6-5.7) in persons with no and unknown vaccination (p <0.0001).

Conclusions

The level of anti-diphtheria toxoid antibodies among children and adults in Kon Tum was low. The high risk of diphtheria outbreaks may occur among individuals lacking basic immunity against diphtheria.