The data presented may therefore be crucial not only for the improvement of classical passive anti-influenza prophylactic and therapeutic strategies [33, 34] , but also for the correct understanding of mechanisms leading to in vivo protective anti-influenza immunity and therefore for the design of more effective vaccinal strategies. Indeed, several pharmacokinetic studies have shown that the extremely low IC 50 featured by PN-SIA28 against most of the isolates tested can easily be reached in humans after systemic administration [35, 36] . Given the frequent correlation between a low IC 50 value and in vivo efficacy observed for other anti-influenza mAbs [25, 26, 27, 28, 29, 30, 31, 37, 38, 39] , PN-SIA28 could be a really promising compound to be used in passive immunization strategies.