This article is from the Childhood Vaccinations FAQ, by Lynn Gazis-Sax firstname.lastname@example.org with numerous contributions by others.
About 70-80% in young, healthy adults. About 50% effective in adults
over 60. (For studies on older adults, see JAMA 1994 Dec 7, N Engl J
Med 1994.) For a summary of recent studies showing benefits in elderly
adults, young children in day care, and healthy adults, see Journal
Watch for January 1, 1996, Volume 16, Number 1, "Top Medical Stories
of 1995." Of particular interest to parents is a study published in
Arch Pediatr Adolesc Medicine, Oct 1995, 149:1113, in which children
at high risk for otitis media (ear infections) showed 32% fewer cases
during the flu season when they received the flu vaccine.
Note that influenza vaccine protects against influenza only, and not
against other respiratory infections.
An intranasal flu vaccine has shown efficacy in trials and may be
available within a year.