Sanofi is challenging influenza rival Seqirus on the regulatory level, arguing labels for two of the CSL Limited subsidiary’s flu shots should be amended to reflect their mixed results in post-approval trials. Seqirus, for its part, says it stands behind the safety and efficacy of its vaccines.
Sanofi made its case to the FDA in a citizen petition published earlier this month. Its complaint hinges on Seqirus’ Fluad–an adjuvanted, trivalent flu shot that snagged accelerated approval in November 2015–and Fluad Quadrivalent, a quadrivalent formulation of the same vaccine that received a speedy green light in Feb. 2020.
For the quadrivalent formulation, Seqirus is on deck to wrap up a confirmatory study by March 31, 2024. Trivalent Fluad, meanwhile, scored accelerated approval in 2015, also on the condition that Seqirus demonstrate the vaccine’s efficacy in a post-approval trial.
Problem is, Seqirus used the quadrivalent formulation in its Fluad confirmatory trial, rather than the trivalent formulation that snagged approval, Sanofi argues. Even then, the quadrivalent formulation missed the mark in efficacy trial V118_18, Sanofi points out.
“Ultimately, the absolute vaccine efficacy was estimated to be 19.80%, which did not meet the pre-specified criterion of lower limit ≥ 40%,” Sanofi wrote in its petition. “The company explained this failure to meet its primary endpoint by stating that most influenza cases were caused by A/H3N2 strains and were antigenically unmatched to the vaccine strain.”
Fluad Quadrivalent did meet a secondary immunogenicity endpoint in the trial, Sanofi added.
The two years in which Seqirus ran Fluad’s confirmatory trial “proved to be challenging seasons to conduct efficacy and effectiveness studies because there was a predominant circulation of A/H3N2 influenza strains which were antigenically unmatched to the vaccine strains chosen by the World Health Organization (WHO),” a Seqirus spokesperson said over email.
The effect of the mismatch was “seen worldwide,” with overall effectiveness of all influenza vaccines lower in older adults–including that of Sanofi’s Fluzone High-Dose shot–the Seqirus spokesperson continued. One “inconclusive study” doesn’t paint the full picture of a seasonal flu shot’s efficacy, she added.