Dynamics of neutralizing secretory influenza antibodies after nasal administration of the NIVGRIP trivalent influenza vaccine.

The trivalent inactivated NIVGRIP influenza vaccine was administered by nasal route to 26 young adults; a matched control group was represented by 19 subjects who received a placebo. Vaccination was followed by a higher proportion of rises in the level of neutralizing secretory antibodies (70-77%) than in that of serum HAI antibodies (19-42%) to the three influenza strains contained in the vaccine. Simultaneous rises in secretory antibody titers to three and two influenza antigens occurred in 50% and 23% of the vaccinees, respectively. The vaccine conferred a protection rate of 75%, as estimated by a 7-month clinical follow-up.