Effect of unequal vaccination coverage and migration on long-term pathogen evolution in a metapopulation

Area of Science:

• Epidemiology
• Evolutionary Biology
• Mathematical Modeling

Background:

• Global vaccine inequalities can influence infectious disease spread and distribution.
• The impact of spatial variation in vaccination coverage on long-term pathogen evolution remains largely unexplored.

Purpose of the Study:

• To analyze how different imperfect vaccines affect pathogen virulence evolution in a two-population model with varying vaccination coverage.
• To investigate the role of spatial heterogeneity, driven by pathogen migration and vaccination rate differences, on pathogen evolution.

Main Methods:

• Utilized an analytical model and numerical simulations.
• Examined four types of imperfect vaccines with distinct modes of action on pathogen life cycles.
• Modeled pathogen dynamics in two host populations connected by migration.

Main Results:

• Vaccines reducing infection risk or transmissibility showed minimal impact on pathogen prevalence, host mortality, and virulence evolution, irrespective of spatial heterogeneity.
• Vaccines reducing pathogen virulence, particularly in heterogeneous metapopulations, can select for increased virulence and promote pathogen strain coexistence.
• The degree of spatial heterogeneity, influenced by pathogen migration and vaccination rate disparities, is a key driver of these evolutionary outcomes.
• Vaccines targeting only virulence primarily select for a single pathogen strategy, while those reducing both transmission and virulence can favor the coexistence of two genotypes.

Conclusions:

• Spatial heterogeneity significantly influences pathogen evolution, especially when vaccines target virulence.
• Vaccine strategies that reduce both transmission and virulence may lead to greater pathogen diversity compared to those targeting only virulence.
• Understanding these dynamics is crucial for predicting and managing infectious disease evolution in the face of global vaccination disparities.