Estimation of Vaccine Effectiveness and Early Recognition of Emerging Flu Strain Clusters

I will discuss evolution of the influenza virus, in the context of the 2017/2018season and historically from 1968 to 2018. Typically a quasispecies of related influenza strains is responsible for the majority of virus in the human population. The virus evolves, however, and this is the reason for the yearly updates to the influenza vaccine. Part of the selection pressure on the virus to evolve arises from immune history in the population due to prior infection or vaccination, which provide protection against closely related strains. This immune protection is well described by the p_epitope theory of vaccine efficacy for both H3N2 and H1N1 influenza. I will discuss this p_epitope theory. As a first application, I will use this theory to explain why the adaptations that occur in the egg-based production lower the effectiveness of the vaccine. In particular, I will show how this theory predicts an effectiveness of 24% for the 2016/2017 vaccine, in comparison to the observed 20%. As a second application, I will discuss interesting recent examples of the emergence of new flu strains, which were not protected against by the vaccine. I will discuss how the emergence of these new strains can be detected and predicted, making use of theory of the immune system.