Modelling trachoma post-2020: opportunities for mitigating the impact of COVID-19 and accelerating progress towards elimination

Abstract

Background: The COVID-19 pandemic has disrupted planned annual antibiotic mass drug administration (MDA) activities that have formed the cornerstone of the largely successful global efforts to eliminate trachoma as a public health problem.

Methods: Using a mathematical model we investigate the impact of interruption to MDA in trachoma-endemic settings. We evaluate potential measures to mitigate this impact and consider alternative strategies for accelerating progress in those areas where the trachoma elimination targets may not be achievable otherwise.

Results: We demonstrate that for districts that were hyperendemic at baseline, or where the trachoma elimination thresholds have not already been achieved after three rounds of MDA, the interruption to planned MDA could lead to a delay to reaching elimination targets greater than the duration of interruption. We also show that an additional round of MDA in the year following MDA resumption could effectively mitigate this delay. For districts where the probability of elimination under annual MDA was already very low, we demonstrate that more intensive MDA schedules are needed to achieve agreed targets.

Conclusion: Through appropriate use of additional MDA, the impact of COVID-19 in terms of delay to reaching trachoma elimination targets can be effectively mitigated. Additionally, more frequent MDA may accelerate progress towards 2030 goals.

Keywords: COVID-19; elimination; modelling; trachoma.

Figure 1.

Schematic of model structure. Individuals can be susceptible to infection (S), infected but not yet diseased (I), infected and diseased (ID) or diseased but having cleared infection (D), where disease refers to trachomatous inflammation—follicular (TF). Individuals for whom infection has been cleared but disease persists (D) can be reinfected with force of infection (reduced by .

Figure 2.

Simulated scenarios for Settings 1 and 2 (interruption and mitigation) and Setting 3 (interruption and mitigation/acceleration protocols). *denotes MDA round targeting children only.

Figure 3.

Median delay (years) to reaching EPHP threshold (TF_1–9<5%) at varying levels of endemicity/stages of trachoma elimination programmes following a 1-y interruption to MDA. Years of MDA indicates the number of rounds of MDA that had been delivered when the last survey was carried out (0 representing baseline survey).

Figure 4.

Median prevalence of TF in children aged 1–9 y (TF_1–9; A and C) and ocular Chlamydia trachomatis infection (B and D). Setting 1 and Setting 2. The black curve represents no disruption to MDA (scenario I in Figure 2), the blue curve represents a 1-y interruption with no mitigation (scenario II in Figure 2) and the red curve represents an additional mitigation round of community-wide MDA given in the year following interruption (scenario M1 Figure 2).

Figure 5.

Median prevalence of TF in children aged 1–9 y (TF_1–9) in Setting 3 (TF_1–9>10% after 10 y of MDA). Adherence correlation parameter ρ = 0, corresponding to no systematic non-compliance. 95% confidence intervals are shown as shaded areas (estimated as 95th centiles). MA1 and MA2 represent mitigation and acceleration strategies described in Figure 2.