Modeling the Potential Impact of Norovirus Vaccination Among DoD Forces

Norovirus, a contagious disease that spreads rapidly in close-quartered communities, has a debilitating effect in military settings, affecting troops' health, productivity, and mission-readiness. This research presents a model of norovirus transmission, testing the vaccination's effectiveness in military training centers.

Transmission was modeled using structured ordinary differential equations, including symptomatic and asymptomatic infection, genetic resistance, vaccination, and herd-immunity effects, within a hypothetical cohort of trainees and support staff. The modeled vaccine had an efficacy of 72%, 4 weeks after a single dose in phase 2 clinical trials. The transmission model was calibrated against data from a norovirus outbreak in a university setting. Sensitivity and uncertainty analyses were performed on 22 parameters.

The greatest reduction in norovirus cases resulted from prophylactic environmental decontamination and vaccination of trainee and staff populations. These combined interventions prevented more than 6,800 cases of norovirus over the 10-year simulated period-a 15% reduction over the baseline scenario of no interventions. Implementing vaccination and environmental decontamination with an outbreak response threshold of 0.1%, prevented more than 5,300 infections; raising the threshold to 0.2% to 0.5% significantly reduced effectiveness. Environmental decontamination and contact reduction alone had little impact on overall norovirus cases.

Given vaccine characteristics, the model predicted that up to 15% of norovirus cases occurring in training settings over a 10-year period could be prevented by vaccinating all trainees and staff members immediately upon arrival on-base combined with continuous environmental decontamination. There was an impact on morbidity from implementing vaccination of trainees, alone and in combination with staff members. However, vaccinating staff alone prevented few cases over the simulation period, indicating the importance of trainees in norovirus transmission. Likewise, the negligible impact of environmental decontamination or contact reduction alone highlights the importance of addressing both person-to-person and environmental transmission together to minimize illnesses and training downtime.