Vaccination as a strategy for Chlamydia trachomatis control: a global mathematical modeling analysis

Abstract

Background: Chlamydia trachomatis (CT) is among the most common sexually transmitted infections and is associated with substantial health and economic burdens. Vaccination may offer a promising strategy for its global control.

Methods: A deterministic, age-structured mathematical model was applied to assess the global impact of a hypothetical CT vaccine. The analysis explored a range of assumptions for vaccine efficacy against infection acquisition ( ${\mathrm{VE}}_S$ ), duration of protection, and coverage, across both adult catch-up and adolescent-targeted vaccination strategies.

Results: Vaccinating individuals aged 15-49 years beginning in 2030 with a vaccine of ${\mathrm{VE}}_S=50\%$ and 20-year protection, scaled to 80% coverage by 2040, reduced global CT prevalence, incidence rate, and annual new infections in 2050 by 26.2%, 32.3%, and 26.5%, respectively. Cumulatively, 717 million infections were averted by 2050. The number needed to vaccinate (NNV) to prevent one infection declined from 23.3 in 2035 to 10.6 in 2050, with variation across population groups: 5.9 for those aged 15-19 years, 7.5 for those aged 10-14 years, and 3.0 for high-risk groups. Vaccine impact increased with higher ${\mathrm{VE}}_S$ , longer protection duration, and inclusion of breakthrough effects on infectiousness and infection duration. While adolescent vaccination achieved substantial impact, its benefits accrued more slowly than those of adult-targeted strategies.

Conclusions: Vaccination against CT can substantially reduce global infection burden, even with moderate efficacy. Impact is enhanced by targeted strategies, with adolescent vaccination aiding long-term control and catch-up programs ensuring immediate benefit. These findings highlight the urgency of vaccine development and integration into public health efforts.

Keywords: Cost-effectiveness; Global health; Number needed to vaccinate; Sexually transmitted infection; Transmission dynamics; Vaccine impact.

Fig. 1

Global impact of the adult CT vaccination scenario targeting individuals aged 15–49 years. Projected reductions in (A) CT prevalence, (B) CT incidence rate, and (C) annual number of new CT infections under the adult vaccination scenario, assuming ${\mathit{VE}}_S$ values of 50%, 70%, and 90%, with a vaccine duration of protection of 20 years. The vaccine is introduced in 2030, and coverage is scaled up to 80% by 2040 and maintained thereafter. Abbreviations: CT, Chlamydia trachomatis

Fig. 2

Global impact of the adolescent CT vaccination scenario targeting individuals aged 10–14 years. Projected reductions in (A) CT prevalence, (B) CT incidence rate, and (C) annual number of new CT infections under the adolescent vaccination scenario, assuming ${\mathit{VE}}_S$ values of 50%, 70%, and 90%, with a vaccine duration of protection of 20 years. The vaccine is introduced in 2030, and coverage is scaled up to 80% by 2040 and maintained thereafter. Abbreviations: CT, Chlamydia trachomatis

Fig. 3

Number needed to vaccinate (NNV) to prevent one CT infection under different vaccination prioritization strategies. A NNV over time since program initiation under the adult CT vaccination scenario. B NNV by age group prioritization by 2050. C NNV by sexual risk group prioritization by 2050. D NNV by sex prioritization by 2050. Analyses assume ${\mathit{VE}}_S=50\%$ and a vaccine duration of protection of 20 years. The vaccine is introduced in 2030, with coverage scaled up to 80% by 2040 and maintained thereafter. Abbreviations: CT, Chlamydia trachomatis

Fig. 4

Number needed to vaccinate (NNV) to prevent one CT infection under the adult vaccination scenario, across varying vaccine characteristics. Projected NNV by 2050 under different assumptions for vaccine efficacy, duration of protection, and coverage levels: A NNV versus ${\mathit{VE}}_S$, assuming a duration of protection of 20 years and 80% vaccine coverage. B NNV versus duration of protection, assuming ${\mathit{VE}}_S=50\%$ and 80% coverage. C NNV versus vaccine coverage level, assuming ${\mathit{VE}}_S=50\%$ and a 20-year duration of protection. The vaccine is introduced in 2030, targeting individuals aged 15–49 years, with coverage scaled to the target level by 2040 and maintained thereafter. Abbreviations: CT, Chlamydia trachomatis

Fig. 5

Global impact of the adult CT vaccination scenario under different combinations of vaccine efficacy parameters. Projected reductions in (A) CT prevalence, (B) CT incidence rate, (C) annual number of new CT infections in 2050, and (D) the number needed to vaccinate (NNV) to prevent one CT infection by 2050, assuming different combinations of ${\mathit{VE}}_S$, ${\mathit{VE}}_I$, and ${\mathit{VE}}_P$, each set at 50%. The vaccine provides 20 years of protection and is introduced in 2030, and coverage is scaled up to 80% by 2040 and maintained thereafter. Abbreviations: CT, Chlamydia trachomatis