Investigating the transmission of baloxavir-resistant influenza viruses from treated index patients to untreated household contacts in the BLOCKSTONE study

Influenza Other Respir Viruses. 2023 Jan;17(1):e13079. doi: 10.1111/irv.13079.


In a post-hoc analysis of the phase 3 BLOCKSTONE study (JapicCTI-184180), we investigated household transmission of baloxavir-resistant (PA/I38X) influenza viruses. Using baloxavir resistance rates from prior clinical trials and the rate of influenza transmission observed in the study, the predicted number of PA/I38X transmission events was 4.8, assuming wild type and PA/I38X viruses were equally transmissible. However, no PA/I38X viruses were observed. These results suggest a low potential for baloxavir-resistant influenza virus transmission from treated to untreated individuals, potentially due to reduced viral/transmission fitness for PA/I38X viruses and/or low viral titres at the time when resistant viruses arise.

Keywords: antiviral agents; baloxavir; drug resistance; influenza; transmission; viral.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Antiviral Agents* / pharmacology
  • Antiviral Agents* / therapeutic use
  • Clinical Trials, Phase III as Topic
  • Drug Resistance, Viral
  • Humans
  • Influenza, Human* / drug therapy
  • Influenza, Human* / epidemiology
  • Pyridines / pharmacology
  • Pyridines / therapeutic use
  • Thiepins / pharmacology
  • Thiepins / therapeutic use


  • Antiviral Agents
  • baloxavir
  • Pyridines
  • Thiepins