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 I-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.