Mutant emergence timing and population immunisation status impact epidemiological dynamics.

Area of Science:

• Epidemiology
• Evolutionary Biology
• Immunology

Background:

• Understanding pathogen evolution and spread is vital, especially for novel infectious diseases.
• Current evolutionary epidemiology models often assume long-lasting immunity, limiting the study of immune escape.
• SARS-CoV-2 variants highlight the need to incorporate realistic immunity dynamics.

Purpose of the Study:

• To investigate the conditions favoring the spread of mutant strains over resident strains.
• To explore the impact of waning immunity and cross-immunity on infectious disease dynamics.
• To analyze the role of immune escape and increased contagiousness in pathogen evolution.

Main Methods:

• Development of a novel two-strains non-Markovian mathematical model.
• Inclusion of realistic immunity waning and cross-immunity dynamics.
• Simulation of fluctuating environmental conditions outside epidemiological equilibrium.

Main Results:

• Mutant strains with increased contagiousness or immune escape capabilities are more likely to invade.
• The timing of mutant strain introduction significantly impacts invasion success, linked to population immunity.
• Immune waning and non-equilibrium dynamics are critical factors in infectious disease evolution.

Conclusions:

• Waning immunity and cross-immunity are essential considerations in evolutionary epidemiology.
• Pathogen traits like immune escape and contagiousness, coupled with introduction timing, drive invasion dynamics.
• Non-equilibrium models provide a more realistic framework for studying infectious disease evolution.