Incidence Rate of COVID-19 Mortality and its Associated Factors During the First and Second Waves in Nigeria: A Retrospective Cohort Study

Abstract

Background: COVID-19 mortality rate has not been formally assessed in Nigeria. We therefore aimed to address this gap and identify associated mortality risk factors during the first and second waves in Nigeria.Methods: We conducted a retrospective cohort study using the national surveillance database between February 27, 2020, and April 3, 2021. The outcome was deaths amongst persons with a laboratory diagnosis of COVID-19. Incidence rates of COVID-19 death per 100,000 person-days were estimated. Adjusted negative binomial regression was used to identify factors associated with COVID-19 death, and presented as adjusted Incidence Rate Ratios (aIRR) with 95% confidence intervals (CI). Results: The first wave included 65,790 COVID-19 patients, of whom 994 (1∙51%) died; the second wave included 91,089 patients, of whom 513 (0∙56%) died. The incidence rate of deaths related to COVID-19 was higher in the first wave [54∙25 (95% CI: 50∙98-57∙73)] than in the second wave [19∙19 (17∙60-20∙93)]. Factors independently associated with increased risk of death in both waves were: age ≥45 years, male gender [first wave aIRR 1∙65 (1∙35-2∙02) and second wave 1∙52 (1∙11-2∙06)], being symptomatic [aIRR 3∙17 (2∙59-3∙89) and 3∙04 (2∙20-4∙21)], and being hospitalised [aIRR 4∙19 (3∙26-5∙39) and 7∙84 (4∙90-12∙54)].Interpretation: The incidence rate of COVID-19 death in Nigeria was higher in the first wave, suggesting improved public health response and care during the second wave. Regional mortality differences suggest that policy makers focus on regional equity in access to testing and quality of care to mitigate the impact of another COVID-19 wave in Nigeria.Funding: None to declare. Declaration of Interest: None to declare. Ethical Approval: Ethical approval for the study was given by the Nigeria National Health Research Ethics Committee (NHREC/01/01/2007-22/06/2020).