Reply to “Studies on Influenza Virus Transmission between Ferrets: the Public Health Risks Revisited”

Lipsitch, Marc; Inglesby, Thomas V.

(ii) The availability and effectiveness of vaccines are not certain. In general, vaccine efficacy even against well-matched seasonal influenza virus varies widely (13) . Some ferret gain-oftransmission experiments involve subtypes for which there are (at the time of the experiment) no licensed vaccines (14) (15) (16) . Moreover, the effectiveness of vaccines and antivirals against laboratory-engineered strains in these experiments is uncertain, even when they are effective against the starting strain; this is why the initial report of ferret-transmissible strains described assays of vaccine neutralization (experiment 7) and antiviral susceptibility (experiment 6) (17) . After performing the experiment, one can retrospectively infer that these protections would have been effective, but at the time of proposing an experiment, neither is certain. Indeed, even after obtaining in vitro results, Fouchier stated that the effectiveness of drugs and vaccines in vivo against the strains produced in his experiments was in doubt and needed testing (18) .