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

Lipsitch, Marc; Inglesby, Thomas V.

While the impact on risk assessment might be to assign less than 100% weight to the scenario of a virulent, pandemic-like strain being released, we believe the same uncertainty negates or even reverses the principal public health benefits claimed for this work. These purported benefits depend on the assumption that mutations found in ferret passage experiments reliably predict pandemic risk. CDC experts state that they have deployed teams to Cambodia based on the presence in H5N1 isolates there of mutations identified in ferret passage experiments (28) and relied on these markers for pandemic threat assessment of H7N9: "Early detection of these molecular markers in H7N9 viruses isolated from humans gave public health authorities evidence that these viruses posed an immediate pandemic threat" (28) . Yet there is no evidence that this reliance has improved decisions by CDC or other public health officials, because we do not know if the strains they identified as high risk actually are higher risk than average. This condition of ignorance stems from the fact that there is no validated predictive algorithm for pandemic risk (37) .