Influenza B vaccine lineage selection--an optimized trivalent vaccine

Abstract

Epidemics of seasonal influenza viruses cause considerable morbidity and mortality each year. Various types and subtypes of influenza circulate in humans and evolve continuously such that individuals at risk of serious complications need to be vaccinated annually to keep protection up to date with circulating viruses. The influenza vaccine in most parts of the world is a trivalent vaccine, including an antigenically representative virus of recently circulating influenza A/H3N2, A/H1N1, and influenza B viruses. However, since the 1970s influenza B has split into two antigenically distinct lineages, only one of which is represented in the annual trivalent vaccine at any time. We describe a lineage selection strategy that optimizes protection against influenza B using the standard trivalent vaccine as a potentially cost effective alternative to quadrivalent vaccines.

Keywords: Decision tree; Hedging; Influenza B; Quadrivalent; Trivalent vaccine; Vaccine strain selection.

Fig. 1

Epidemic time series for B/Vic (red) and B/Yam (blue) based on virologically confirmed data from the WHO Collaborating Centers for Reference and Research on Influenza. The counts of each variant are the numbers of viruses tested antigenically by the collaborating centers. Numbers are assumed to be representative of the relative proportion of viruses that circulated. Time series were logged and smoothed with a weighted moving average to capture trends.

Fig. 2

Example decision tree. A representative of B/Yam or B/Vic strain has to be chosen for the vaccine. Both choices lead to two possible outcomes: the vaccine lineage dominates (outermost branches of the tree), or the non-vaccine lineage dominates (innermost branches of the tree).

Fig. 3

Predicted protection levels for the seasons 2000/2001 to 2009/2010 for each of the three lineage selection strategy.