Cross immunity and vaccination against multiple microparasite strains

Area of Science:

• Mathematical epidemiology
• Theoretical ecology
• Immunology

Background:

• Pathogen evolution involves interactions between different strains.
• Immune priming following infection with one strain can affect subsequent infections.
• Understanding these interactions is crucial for predicting disease dynamics.

Purpose of the Study:

• To explore equilibrium properties of compartmental ODE models for multi-strain pathogen interactions.
• To investigate how antigenic similarity and host immune history affect strain coexistence.
• To analyze the impact of vaccination on multi-strain pathogen dynamics.

Main Methods:

• Development and analysis of compartmental Ordinary Differential Equation (ODE) models.
• Modeling host immune responses, including susceptibility and transmission, based on infection history.
• Examination of equilibrium conditions for strain coexistence in SIR and SIS models.

Main Results:

• In SIR models, increased antigenic similarity between strains reduces the parameter space for coexistence.
• In SIS models, strain coexistence depends on recovery rates and differential infectivity of strains.
• Maximum of two strains can coexist in the SIS model, with analogies to commensalism and symbiosis.
• Vaccination can alter strain dominance, potentially allowing excluded strains to emerge or rare strains to increase.

Conclusions:

• Host immune history and antigenic similarity are key determinants of multi-strain pathogen dynamics.
• SIS models offer insights into ecological interactions like commensalism and symbiosis.
• Vaccination strategies must consider initial strain structure and vaccine efficacy for effective control.
• Findings are relevant to understanding pathogens like rotavirus.