Control of pandemic (H1N1) 2009 influenza virus infection of ferret lungs by non-adjuvant-containing pandemic and seasonal vaccines.

The pandemic H1N1 2009 influenza virus caused relatively mild disease in most infected people but some suffered extensively from primary lung infection, many more than would have occurred with seasonal influenza infection. Early commercially available pandemic H1N1 vaccines did not contain adjuvant, as did many of the subsequent vaccines, and could not stop infection with the pandemic virus in vaccinated ferrets. Nevertheless, we showed that virus loads in the lungs were greatly diminished in ferrets vaccinated once with an unadjuvanted pandemic vaccine and challenged with 10(6)EID(50) wildtype A/California/07/2009 (H1N1). In addition, a single inoculation with seasonal vaccine showed beneficial reduction in pandemic pulmonary virus loads in the absence of any detectable cross-reactive serological responses. Ferrets primed with either seasonal or pandemic vaccine and then boosted with pandemic vaccine also showed less extensive lung infection when challenged with a tenfold higher dose of pandemic virus. These results implicate non-classical protective mechanisms that prevent severe pulmonary disease but not viral shedding and imply that particular non-adjuvanted vaccines may have retained the ability to induce these responses.