In vitro NK cell responses to components of the DTP vaccine (diphtheria toxoid, tetanus toxoid and whole cell inactivated pertussis), Bacille Calmette–Guérin (BCG) and influenza vaccine are enhanced after vaccination14, 21, 22, 23 and heightened NK cell IFN‐γ and degranulation responses have been detected after vaccination against rabies.24 In contrast to the memory responses described above, these postvaccination responses are dependent on vaccine‐specific CD4+ memory T cells and, in particular, their rapid secretion of IL‐2.23, 24. Here, CD4 is linked to influenza.