Defining Seasonal Areas
WHO 4-month rule applied with a rolling-window method to classify locations as seasonal or not seasonal.
Seasonality
Methods for classifying malaria seasonality and timing seasonal interventions.
Overview
Seasonality refers to predictable, yearly changes driven by environmental factors such as rainfall, temperature, and humidity. In malaria, these changes matter because mosquito breeding and transmission depend heavily on rainfall. During rainy months, mosquito numbers and malaria cases rise; in dry months, breeding diminishes and cases drop.
Understanding these patterns helps programs plan when and where to act. Interventions such as Seasonal Malaria Chemoprevention (SMC), ITN distribution, and IRS campaigns are most effective when scheduled before or during the high-transmission season.
NoteObjectives
- Identify areas with a seasonal rainfall pattern linked to predictable malaria transmission
- Classify locations as seasonal or non-seasonal using the WHO 4-month rule
- Compare alternative window durations (2-, 3-, 4-, 5-month blocks) to inform SMC timing
- Produce maps and summaries for program decision-making
ImportantConsult the SNT team
Seasonality thresholds and window durations come from WHO recommendations, but rainfall and transmission patterns vary by country. Before applying or adjusting these rules:
- Confirm the threshold (e.g., 60%) and window length are appropriate for the local context
- Adjust if rainfall or malaria data show different timing patterns
- Document and justify any modification to ensure national consistency