Studies on Influenza Virus Transmission between Ferrets: the Public Health Risks Revisited

Fouchier, Ron A. M.

A final factor to consider in the calculation of the probability of onward transmission from each case of LAI is the basic reproduction number (R0) of the influenza virus under investigation. As indicated above, the previous risk assessments were based on R0 of pandemic influenza virus. However, laboratory experiments have shown that the efficiency of transmission of the laboratoryderived influenza viruses was lower than that of the transmission of pandemic and seasonal influenza viruses in ferrets, as could be Letter to the Editor expected (12, 16, 26) . Moreover, given that the viruses are ferret adapted rather than human adapted, even an extremely conservative adjustment of the transmissibility parameter by a factor of 2 would yield a "final" estimation of the probability of onward transmission from a case of LAI of Ͻ2.5 ϫ 10 Ϫ6 to 3 ϫ 10 Ϫ5 .