Prevalence, trend and climatic associations of influenza in under-five children in Zambia, 2024

Abstract

Introduction: Worldwide, influenza causes about 3-5 million cases of severe respiratory illnesses and 650000 deaths in children every year. In Zambia, transmission peaks during the dry cool season (May–August). Understanding prevalence, trends, and climatic influences can guide prevention strategies. The study set out to determine the prevalence, seasonal trend, and climatic associations of influenza in under five over a 11-year period. Methods: We conducted a retrospective longitudinal study (2014–2024) using data from 14 Severe acute respiratory illness / Influenza like illness (SARI/ILI) sentinel surveillance sites across Zambia. Children under-five years with laboratory-confirmed influenza were included. Surveillance data were linked with climatic variables (temperature, rainfall, humidity) collected by the Zambia Meteorology Department and NASA POWER. Descriptive analyses summarized Influenza prevalence and subtype distribution; autoregressive integrated moving average (ARIMA) and Poisson models assessed time-series patterns and associations of influenza incidence to climatic variables respectively. Results: Among 12,296 under-five SARI/ILI cases, 1,212 (9.8%) tested positive for influenza. Prevalence peaked in 2019 (14.6%) and was lowest in 2020 (0.7%) during the COVID-19 pandemic; no significant linear trend was observed (p=0.142). Influenza A (63.5%, mainly H3N2) predominated over Influenza B (36.5%). Distinct seasonal patterns were noted, with peaks in the dry-cool season. Influenza activity was found to be moderately persistent from month-month (p = 0.009) and seasonal (p < 0.001). The ARIMA forecasted continue Influenza seasonal pattern until 2026. Higher average monthly temperature and higher humidity reduced influenza incidence by 7% (IRR= 0.922, p < 0.001) and 2% (IRR = 0.98, p < 0.001), respectively. Rainfall effects were not significant. Conclusion: The prevalence of Influenza in under -five was 9.8% with the dry-cool season being the peak season. Average monthly temperatures and humidity were negatively associated with Influenza cases. Strengthened surveillance and preparedness during the dry-cool months are essential for prevention and control.