A double-blind trial of a new inactivated, trivalent, intra-nasal anti-influenza vaccine in general practice: relationship between immunogenicity andrespiratory morbidity over the winter of 1997-98

Background: Influenza is responsible for considerable morbidity not only am ong older people but in younger age groups as well. However, most large-sca le anti-influenza vaccination campaigns are still aimed principally at the elderly using injectable vaccines. Until now there has been much less empha sis on targeting younger populations or using intra-nasal vaccines in mass anti-influenza immunisation programmes. Objectives: To assess the immunogen icity of a new inactivated intra-nasal anti-influenza vaccine and to measur e its effect on respiratory morbidity in a volunteer general practice popul ation. Study design: A prospective, double-blind, placebo-controlled trial using the new vaccine was carried out over the winter of 1997-98 on 274 hea lthy patients aged 12-60 from three Israeli general practices, 182 in the v accine group and 92 in the placebo group. Following vaccination the changes in the antigen levels and episodes of respiratory illness in the vaccine a nd placebo groups were measured. Results: Protective antibody levels occurr ed after a single dose of vaccine [influenza HIN1, 41% immune pre-vaccinati on to 73% post-vaccination; influenza H3N2, 35-66%; influenza B, 27-64%]. B etween January and March 1998, when influenza activity was at a peak in Isr ael, the average number of respiratory illness events in the vaccine group [14 events/100 subjects per month] was significantly less than in the place bo group [22 events/100 subjects per month]; similarly, the average number of respiratory illness days in the vaccine group over the same period [69 d ays/100 subjects per month] was significantly less than in the placebo grou p [117 days/100 subjects per month]. Conclusions: The new vaccine possessed significant immunogenicity and was associated with a significant reduction in respiratory morbidity among a group of healthy older children and adult s. Since intra-nasal vaccine's are simpler to administer and more acceptabl e to the public than injections the vaccine's potential for use in routine anti-influenza vaccination campaigns seems promising, especially if its ben eficial effects are also reproducible in more medically vulnerable populati ons. (C) 2001 Elsevier Science B.V. All rights reserved.