Impact of the COVID-19 pandemic on reported malaria incidence in children under five years of age in Cameroon: an interrupted time series analysis with regional heterogeneity (2017–2022)

BACKGROUND: Malaria remains a major cause of childhood morbidity and mortality in Cameroon. The COVID-19 pandemic disrupted access to healthcare and the continuity of malaria control programmes; however, its impact on reported incidence among children under 5 years of age, and its regional heterogeneity, remain insufficiently studied. We aimed to estimate the impact of the COVID-19-related interruption on reported malaria incidence among children under five years of age in Cameroon, nationally and by region, using routine DHIS2 surveillance data from 2017 to 2022. METHODS: We conducted an interrupted time series (ITS) study using monthly DHIS2 data from January 2017 to December 2022. Reported malaria incidence among children under 5 years of age was modelled using negative binomial regression (NB2) with a population offset. Two interruption points were defined a priori: March 2020 and January 2022. The model controlled for monthly fixed effects, long-lasting insecticidal net (LLIN) distribution activity, seasonal malaria chemoprevention (SMC) activity, the paediatric consultation rate, and one-month lagged rainfall. Inference relied on Newey-West HAC-robust standard errors (lag = 12). Regional ITS models, counterfactual analysis, and sensitivity analyses complemented the primary analysis. RESULTS: In March 2020, reported incidence showed an immediate 36.9% decline relative to the pre-pandemic trend (D1: IRR = 0.631; 95% CI 0.539-0.738; p < 0.001), followed by a positive slope change of 3.1% per month (P1: IRR = 1.031; 95% CI 1.017-1.045; p < 0.001). The second interruption point was not associated with any significant change in level or slope. The LLIN distribution indicator was inversely associated with reported incidence (IRR = 0.978; 95% CI 0.960-0.997; p = 0.024). Counterfactual analysis estimated a deficit of 69,708 notifications over 2020-2021, followed by an excess of 74,831 in 2022. Marked regional heterogeneity was observed, with particularly severe initial declines in the Centre (IRR = 0.467) and East (IRR = 0.544) regions. CONCLUSIONS: The COVID-19 pandemic was associated with a substantial initial disruption in reported childhood malaria incidence in Cameroon, followed by a progressive recovery with marked territorial disparities. These findings support strengthening the continuity of malaria services during crises and maintaining high-quality surveillance systems to enable regionally tailored programmatic decision-making.