From trivalent to quadrivalent influenza vaccines: Public health and economic burden for different immunization strategies in Spain.

Purpose: Quadrivalent influenza vaccine (QIV) includes the same strains as trivalent influenza vaccine (TIV) plus an additional B strain of the other B lineage. The aim of the study was to analyse the public health and economic impact of replacing TIV with QIV in different scenarios in Spain. Methods: A dynamic transmission model was developed to estimate the number of influenza B cases prevented under TIV and QIV strategies (