On Dec. 5, 2018, Seqirus, a CSL subsidiary, announced real-world data showing that its cell-based quadrivalent influenza vaccine (QIVc) was 36.2 percent more effective than standard egg-based quadrivalent vaccines (QIVe) in preventing influenza-like illnesses during the 2017/18 influenza season in the United States. This is likely due to the predominance of the H3N2 virus and its propensity for mutation when it is adapted for influenza vaccine production in chicken eggs.

The finding was based on an analysis of over one million (1,353,862) medical records for patients aged four years and above who received either a four-strain egg-based influenza vaccine or a four-strain cell-based influenza vaccine in a primary care setting during the 2017/18 influenza season in the United States. According to the US Centers for Disease Control the 2017/18 influenza season in the U.S. was the worst in recent years with the H3N2 virus being associated with the majority of influenza infections. Research has shown that H3N2 viruses often undergo changes when they are grown in eggs.

QIVc was first licensed in the U.S. in 2016 based on a study showing non-inferiority immune response to a three-strain cell-based influenza vaccine. Both cell-based products used in this study were produced using egg-based starting viruses8. The 2017/18 season was the first in which QIVc was manufactured using a cell-derived H3N2 starting virus, making this component of the vaccine exclusively cell-based.