Evaluating the fitness of PA/I38T-substituted influenza A viruses with reduced baloxavir susceptibility in a competitive mixtures ferret model

Leo YY Lee, Jie Zhou, Paulina Koszalka, Rebecca Frise, Rubaiyea Farrukee, Keiko Baba, Shahjahan Miah, Takao Shishido, Monica Galiano, Takashi Hashimoto, Shinya Omoto, Takeki Uehara, Edin J. Mifsud, Neil Collinson, Klaus Kuhlbusch, Barry Clinch, Steffen Wildum, Wendy S. Barclay, Aeron C. Hurt

Research output: Contribution to journalArticleResearchpeer-review

16 Citations (Scopus)


Baloxavir is approved in several countries for the treatment of uncomplicated influenza in otherwise-healthy and high-risk patients. Treatment-emergent viruses with reduced susceptibility to baloxavir have been detected in clinical trials, but the likelihood of widespread occurrence depends on replication capacity and onward transmission. We evaluated the fitness of A/H3N2 and A/H1N1pdm09 viruses with the polymerase acidic (PA) I38T-variant conferring reduced susceptibility to baloxavir relative to wild-type (WT) viruses, using a competitive mixture ferret model, recombinant viruses and patient-derived virus isolates. The A/ H3N2 PA/I38T virus showed a reduction in within-host fitness but comparable between-host fitness to the WT virus, while the A/H1N1pdm09 PA/I38T virus had broadly similar within-host fitness but substantially lower between-host fitness. Although PA/I38T viruses replicate and transmit between ferrets, our data suggest that viruses with this amino acid substitution have lower fitness relative to WT and this relative fitness cost was greater in A/H1N1pdm09 viruses than in A/H3N2 viruses.

Original languageEnglish
Article numbere1009527
Number of pages24
JournalPLoS Pathogens
Issue number5
Publication statusPublished - 6 May 2021

Cite this