Serum and mucosal immunologic responses in children following the administration of a new inactivated intranasal anti-influenza vaccine

Children are at considerable risk for influenza infection and may constitut e the main vector for transmitting the virus to adults in the community. At present, the use of available vaccines in children is limited mainly becau se of a fear of side effects from the injection. Intranasal immunization wa s assessed as a painless, side effect-free method of facilitating the enrol lment of children in vaccination programs. One intranasal dose of a trivale nt inactive whole virus vaccine containing 20 mug of the three recommended seasonal viral strains was administered to 28 children recruited over two s eparate winter periods (1997/1998 and 1998/1999). No adverse effects were r ecorded. Serum IgG responses were determined by the hemagglutination inhibi tion (HI) method and nasal IgA responses by enzyme-linked immunosorbent ass ay (ELISA). In both study period seasons, 77.7%-94.4% of children were foun d to be immune. There was a 3.7 x and 4.7 x increase in geometric mean tite r (GMT) for A/H3N2 strains, 1.9 x and 3.9 x for A/H1N1 strains, and a 3.2 x and 1.7 x for B strains in 1997/1998 and 1998/1999, respectively. The incr ease in GMT, as well as fourfold increases in titer level, was higher when calculated among the nonimmune children prior to vaccination. Of these, 50% -87.5% became immune following immunization. Local antibody response to the three viral strains was detected in 50%-55% of the immunized children. Als o, 83.3%, 73.3%, and 61.1% of the vaccinees exhibited a mucosal and/or seru m antibody response to the A/Beijing, A/Sydney, and B/Harbin strains, respe ctively. This mucosal response may forestall influenza development in its e arly stages, thereby contributing significantly to the reduction of influen za spread in the community. (C) 2001 Wiley-Liss, Inc.