The linked case-control study by Garcia-Garcia and colleagues (doi:10.1136/bmj.b3928) shows that, contrary to earlier speculation, some level of cross protection against the new influenza A/H1N1 virus may be provided by the 2008-9 seasonal flu vaccine.1 In a group of 60 confirmed infected and 180 uninfected controls, uninfected people were significantly more likely to have received the seasonal flu vaccine (29% v 13%). Turning the data around, of the 179 unvaccinated people in the study, 52 (29%) became infected with pandemic H1N1 whereas eight of 61 (13%) vaccinated people became infected. Furthermore, all of these eight people survived, whereas 18 of the 52 unvaccinated people who were infected died. Despite the study’s limitations, the data suggest that vaccination with the seasonal flu vaccine confers some protection against pandemic H1N1 virus infection and severe disease from this infection.

Although these observations agree with recently reported low rates of seroconversion to new H1N1 specific antibodies after seasonal vaccination in adults,2 the authors emphasise that their observations do not …