Emerging H7N9 influenza virus infections in Asia have once more spurred the development of effective pre-pandemic H7 vaccines. However, many vaccines based on avian influenza viruses - including H7 - are poorly immunogenic as measured by traditional correlates of protection. Here we re-evaluated sera from an H7N1 human vaccine trial performed in 2006. We examined cross-reactive antibody responses to divergent H7 strains including H7N9, dissected the antibody response into head versus stalk reactive antibodies, and tested the in vivo potency of these human sera in a passive transfer H7N9 challenge experiment in mice. Although only a low percentage of vaccinees induced neutralizing antibody responses against the homologous vaccine strain and also H7N9, we detected strong cross-reactivity to divergent H7 HAs in a large proportion of the cohort using a quantitative ELISA method. Furthermore, H7N1 vaccination induced antibodies to both the head and the stalk domain of the HA which is in sharp contrast to seasonal inactivated vaccines. Finally, we were able to show that both, neutralizing but also non-neutralizing antibodies improved in vivo virus clearance in a passive transfer H7N9 challenge mouse model.