Brennhofer, Stephanie A., Platts-Mills, James A., Lewnard, Joseph A., Liu, Jie, Houpt, Eric R., and Rogawski McQuade, Elizabeth T.
Background: Shigella is a leading cause of diarrhea and dysentery in children in low-resource settings, which is frequently treated with antibiotics. The primary goal of a Shigella vaccine would be to reduce mortality and morbidity associated with Shigella diarrhea. However, ancillary benefits could include reducing antibiotic use and antibiotic exposures for bystander pathogens carried at the time of treatment, specifically for fluoroquinolones and macrolides (F/M), which are the recommended drug classes to treat dysentery. The aim of the study was to quantify the reduction in Shigella attributable diarrhea, all diarrhea, and antibiotic use in the first 2 years of life that could be prevented by a Shigella vaccine. Methods and findings: We used data from the Etiology, Risk Factors, and Interactions of Enteric Infections and Malnutrition and the Consequences for Child Health and Development (MAL-ED) study, a birth cohort study that followed 1,715 children with twice weekly surveillance for enteric infections, illnesses, and antibiotic use for the first 2 years of life from November 2009 to February 2014 at 8 sites. We estimated the impact of 2 one-dose (6 or 9 months) and 3 two-dose (6 and 9 months, 9 and 12 months, and 12 and 15 months) Shigella vaccines on diarrheal episodes, overall antibiotic use, and F/M use. Further, we considered additional protection through indirect and boosting effects. We used Monte Carlo simulations to estimate the absolute and relative reductions in the incidence of diarrhea and antibiotic use comparing each vaccination scenario to no vaccination. We analyzed 9,392 diarrhea episodes and 15,697 antibiotic courses among 1,715 children in the MAL-ED birth cohort study. There were 273.8 diarrhea episodes, 30.6 shigellosis episodes, and 457.6 antibiotic courses per 100 child-years. A Shigella vaccine with a mean vaccine efficacy of 60% against severe disease given at 9 and 12 months prevented 10.6 (95% CI [9.5, 11.5]) Shigella diarrhea episodes of any severity per 100 child-years (relative 34.5% reduction), 3.0 (95% CI [2.5, 3.5]) F/M courses for Shigella treatment per 100 child-years (relative 35.8% reduction), and 5.6 (95% CI [5.0, 6.3]) antibiotic courses of any drug class for Shigella treatment per 100 child-years (relative 34.5% reduction). This translated to a relative 3.8% reduction in all diarrhea, a relative 2.8% reduction in all F/M courses, a relative 3.1% reduction in F/M exposures to bystander pathogens, and a relative 0.9% reduction in all antibiotic courses. These results reflect Shigella incidence and antibiotic use patterns at the 8 MAL-ED sites and may not be generalizable to all low-resource settings. Conclusions: Our simulation results suggest that a Shigella vaccine meeting WHO targets for efficacy could prevent about a third of Shigella diarrhea episodes, antibiotic use to treat shigellosis, and bystander exposures due to shigellosis treatment. However, the reductions in overall diarrhea episodes and antibiotic use are expected to be modest (<5%). Leveraging data from 1715 children in the MAL-ED birth cohort study, Stephanie A Brennhofer and colleagues model the expected reduction in diarrhea episodes, antibiotic use, and bystander pathogen exposure to antibiotics through the administration of Shigella vaccines. Author summary: Why was this study done?: Shigella is a leading cause of diarrhea and dysentery among children under 5 years of age in low- and middle- income countries (LMICS). There are several Shigella vaccines in the pipeline poised to reduce mortality and moderate-to-severe diarrhea episodes. The World Health Organization (WHO) has specified that a preferred Shigella vaccine would have a minimum of 60% vaccine efficacy against moderate-to-severe diarrhea, be 1 to 2 doses, and the series would be completed before 12 months of age. WHO has encouraged estimating antibiotic use as a secondary endpoint in Shigella vaccine trials. What did the researchers do and find?: We performed Monte Carlo simulations using data from 1,715 children in the Etiology, Risk Factors, and Interactions of Enteric Infections and Malnutrition and the Consequences for Child Health and Development (MAL-ED) birth cohort study to estimate the expected reduction in diarrhea episodes, antibiotic use, and bystander pathogen exposure to antibiotics through the administration of 1- and 2-dose Shigella vaccines given at varying ages to coincide with vaccines currently administrated in the Expanded Programme on Immunization (EPI) schedule. Vaccine efficacy was simulated using a beta distribution with a mean vaccine efficacy of 60% or 80% for severe diarrhea. A 2-dose Shigella vaccine with 60% efficacy given at 9 and 12 months could reduce 34.5% of Shigella diarrhea episodes, 34.5% of antibiotic courses to treat Shigella, and 33.9% of antibiotic exposures to bystander pathogens to treat shigellosis. A 2-dose Shigella vaccine with 60% efficacy given at 9 and 12 months could reduce 3.8% of diarrhea episodes of any etiology, 0.9% of antibiotic courses for diarrhea overall, and 1.1% of all antibiotic exposures to bystander pathogens. What do these findings mean?: A Shigella vaccine could considerably reduce Shigella-associated diarrhea and antibiotic use but will likely have a modest effect on all-cause diarrhea and antibiotic use. The MAL-ED study sites may not reflect the expected impact of a Shigella vaccine in all low-resource settings. Future studies should account for varying vaccine efficacy by Shigella species and serotypes and consider waning immunity over a longer follow-up period. [ABSTRACT FROM AUTHOR]