Assessment of efficacy and safety of pandemic A/H1N1/2009 influenza vaccine in a group of health care workers

Introduction: The development in an extremely short time of an efficacious and safe vaccine against the pandemic A/H1N1 virus was a challenge that involved the entire scientific community. Aims: To assess the immunological and clinical efficacy of the new H1N1v monovalent influenza vaccine (Focetria ^® Novartis Vaccines, Siena, Italy) in a group of health care workers (HCWs). Methods: A total of 148 volunteer HCWs were enrolled between Mid-Novembre 2009 and December 2009. After measuring antibody titers, a single intramuscular dose of 7.5 μg of Focetria ^® monovalent vaccine against A/H1N1/2009 influenza virus with MF59C.1 adjuvant was administered. Results: Antibody titers (median value) before and after a single dose of vaccine, measured by means of standard heamagglutination inhibition test (HAI), increased from 32 to 256 (p<0.001). After vaccination, 79.7% of the subjects showed antibody seroconversion, and in 97.3% seroprotecion was achieved. The ratio between the geometric means of antibody titers (GMTR) was 6.69. For the 3 subjects who reported symptoms of ILI (Influenza-like illness), a regular nasal-pharyngeal swab sample was taken to identify the virus type by RT-PCR, the laboratory results of tests performed on these samples were negative for pandemic A/H1N1/2009 virus. During the entire follow-up period of 6 months no severe adverse events occurred. Conclusions: The vaccine against pandemic A/H1N1/2009 virus provided protection against the virus and not only contributed to a significant immunization (according to EMEA criteria), but kept all 148 subjects under study free from A/H1N1/2009 influenza illness.