Investigating Climate-Driven Disruption of Malaria Transmission Following the 2022 Sindh, Pakistan Floods: An Interrupted Time Series Study

Malaria remains a major global public health challenge in developing countries, with climate change intensifying its impact, particularly in vulnerable populations. Rising temperatures can expand the geographic range and local abundance of malaria vectors, Anopheles mosquitoes, which thrive in warm climates, with 25C representing the optimal temperature for malaria transmission. In Pakistan, malaria is primarily spread through P. falciparum and P. vivax. Pakistan is one of the seven countries in the Eastern Mediterranean Region that accounts for 98% of the total malaria burden in the region. Recently, after catastrophic flooding in Pakistan in 2022 and the subsequent increase in malaria incidence, it has become imperative to estimate the climate change-attributed increase in the risk of malaria. In this study, we analyze the time series malaria case incidence data from the province of Sindh, Pakistan, and the climate data to quantify climate-attributed malaria cases in Sindh, Pakistan. We fit a negative binomial generalized linear model (GLM) to monthly case counts with interrupted time series and seasonality terms. The majority of malaria-confirmed infections were Plasmodium Vivax (40-95%) between 2016-2024, followed by Plasmodium falciparum infections. The positivity rate for malaria remained <10% until June 2022, and increased massively after the July 2022 flooding. After accounting for this case momentum, the onset of the 2022 floods was associated with an immediate, independent increase in malaria cases of approximately threefold (IRR 2.985, 95% CI 1.878-4.751, p < 0.001). These findings suggest that post-flooding malaria surveillance and response in flood-affected settings should anticipate not only an acute environmentally driven surge in cases but also a subsequent period of elevated, self-sustaining transmission that may persist well beyond the resolution of the initiating environmental disruption, in this case the flooding.