Projecting excess mortality due to infectious diseases during a crisis: methods and application to the Gaza Strip, 2023-2024.

Excess mortality is a key consequence of crises due to armed conflicts and natural disasters. Israel's campaign in the Gaza Strip has exposed people to multiple risk factors for increased infectious disease burden. We developed a novel method for forward-projecting mortality due to both endemic and epidemic-prone infections in Gaza between 7 October 2023 and 6 August 2024. After defining alternative crisis scenarios, we used expert elicitation to quantify the probability of specific epidemics and increases in transmissibility and case fatality. We analysed past vaccination coverage and natural exposure information to estimate population susceptibility. For endemic infections, we multiplied pre-war mortality by the above parameters. For epidemics, we simulated a susceptible-exposed-infected-recovered process. We estimated that about 4000 endemic infection deaths would occur under a status quo scenario, ranging from 3400 to 4600 under ceasefire and escalation scenarios and comprising mainly COVID-19, influenza and pneumococcal disease. For epidemics, we projected 8500 deaths but with a wide 95% confidence interval; cholera, measles and polio were the most likely threats. The method generated actionable projections under a single analytic framework but should be strengthened, e.g. by explicitly featuring the effect of malnutrition and strengthening expert elicitation techniques before generalizing it to other crises.