PARENT SESSION
Contributed Oral Session 97 : Toxicology and Disease: Modeling; Dynamics
Wednesday, August 10, 1:30 PM - 5:00 PM, Meeting Room 518 A, Level 5, Palais des congrès de Montréal
Antigenic drift of the influenza virus and the risk of sudden vaccine breakdown.
Park, Andrew*,1, 3, 4, Daly, Janet4, Wood, James3, 4, Gog, Julia3, Grenfell, Bryan2, 3, 1 Queen's University, Kingston, Canada3 Cambridge University, Cambridge, UK4 Animal Health Trust, Newmarket, UK2 The Pennsylvania State University, Pennsylvania, USA
ABSTRACT- Influenza vaccines, although imperfect, protect individuals and reduce the extent of epidemics. Vaccine efficacy relies on a close match between vaccine and circulating strains. Mutations during viral replication within a host and selection pressure from pre-existing immunity result in viral evolution. Consequently, vaccines are updated frequently. However, the relationship between epidemic risk and viral evolution is not well understood, yet has profound consequences for influenza epidemiology and ecology. Here we bridge scales from the amino acids of a key viral protein (hemagglutinin) to the population-level epidemiology of influenza using a combination of data analysis from equine studies and mathematical modeling to evaluate the risk posed by an evolving virus in a vaccinated population. Our results show that vaccine breakdown is not gradual but rather there are a critical number of mutations beyond which vaccine efficacy sharply deteriorates. This critical number of mutations depends on the rate at which: (i) probability of becoming infected; (ii) probability of shedding virus; and (iii) infectious period change with antigenic drift. These factors combine to alter the effective reproductive number. Once this number exceeds the threshold value of unity the population is no longer protected. Our analysis indicates that few mutations (in the epitopic regions of the hemagglutinin protein) are required to render a vaccine ineffective. Reappraisal of existing human influenza data indicates that this effect could be seen in man.
Key words: influenza, evolution, epidemiology, vaccine