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

Abstract Children are at considerable risk for influenza infection and may constitute the main vector for transmitting the virus to adults in the community. At present, the use of available vaccines in children is limited mainly because of a fear of side effects from the injection. Intranasal immunization was assessed as a painless, side effect‐free method of facilitating the enrollment of children in vaccination programs. One intranasal dose of a trivalent inactive whole virus vaccine containing 20 μg of the three recommended seasonal viral strains was administered to 28 children recruited over two separate winter periods (1997/1998 and 1998/1999). No adverse effects were recorded. Serum IgG responses were determined by the hemagglutination inhibition (HI) method and nasal IgA responses by enzyme‐linked immunosorbent assay (ELISA). In both study period seasons, 77.7%–94.4% of children were found to be immune. There was a 3.7 × and 4.7 × increase in geometric mean titer (GMT) for A/H3N2 strains, 1.9 × and 3.9 × for A/H1N1 strains, and a 3.2 × and 1.7 × for B strains in 1997/1998 and 1998/1999, respectively. The increase 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. Also, 83.3%, 73.3%, and 61.1% of the vaccinees exhibited a mucosal and/or serum antibody response to the A/Beijing, A/Sydney, and B/Harbin strains, respectively. This mucosal response may forestall influenza development in its early stages, thereby contributing significantly to the reduction of influenza spread in the community. J. Med. Virol. 65:178–184, 2001. © 2001 Wiley‐Liss, Inc.