Investigating persistent measles dynamics in Niger and associations with rainfall

Area of Science:

• Epidemiology
• Public Health
• Infectious Disease Dynamics

Background:

• Measles remains a significant cause of child mortality in sub-Saharan Africa.
• Current immunization strategies face challenges in achieving high coverage due to unique transmission drivers in the region.
• Understanding measles persistence is crucial for enhancing vaccination coverage and reducing transmission.

Purpose of the Study:

• To analyze measles transmission mechanisms in Niger.
• To identify dominant periodicities and spatial clustering patterns of measles cases.
• To investigate the association between measles cases and environmental factors like rainfall.

Main Methods:

• Analysis of weekly reported measles cases at the district level in Niger (1995-2004).
• Identification of dominant periodicities using spectral analysis.
• Investigation of spatial clustering patterns.
• Correlation analysis with environmental drivers, including rainfall.

Main Results:

• Dominant annual and 2-3-year periodicities were identified in measles reporting.
• The annual periodicity exhibited strong, stable, contiguous spatial clustering, linked to population density gradients.
• The 2-3-year periodicities were weaker, unstable, and spatially fragmented.
• Rainy seasons showed a reduced risk of measles case reporting.

Conclusions:

• The annual measles periodicity in Niger is likely driven by seasonal agricultural labor migration.
• The 2-3-year periodicity may result from factors like disease reintroductions and varied vaccine coverage.
• Targeting seasonal mobile populations with improved vaccination strategies could mitigate measles seasonality and reduce transmission.