Cytotoxic T lymphocyte responses of infants after natural infection or immunization with live cold‐recombinant or inactivated influenza A virus vaccine

The cytotoxic T lymphocyte (CTL) response of infants after immunization with either inactivated trivalent subvirion vaccine (TIV) or bivalent attenuated cold‐recombinant (CR) vaccine or occurrence of natural influenza virus infection were compared in a blinded, placebo‐controlled study during the 1987–1988 and 1988–1989 influenza epidemic seasons. Healthy infants between 6 and 13 months of age were randomly assigned and administered a single dose of intranasal bivalent (A/H3N2/A/H1N1) CR vaccine, a two‐dose regimen of TIV (A/H3N2/A/H1N1/B) influenza vaccine, or placebo. Peripheral blood lymphocytes were obtained prior to and 2–8 weeks after vaccination and at the end of the epidemic season and stimulated with virus in vitro for 6 or 7 days. Lysis of autologous virus‐infected target cells was assessed in a 4 hr 51Cr release assay. MHC class l‐restricted influenza A‐specific CTL was stimulated following natural influenza A virus infection but not after immunization with CR influenza A virus vaccine or TIV. These results demonstrate for the first time induction of influenza virus‐specific CTL activity in infants under 1 year of age. © 1996 Wiley‐Liss, Inc.