Is the adjuvanted influenza vaccine more effective than the trivalent inactivated vaccine in the elderly population? Results of a case-control studyVittoria Colamesta

Background Influenza illness is an important public health problem and annual vaccination is globally recommended for high risk populations. In the elderly the vaccine effectiveness is lower, compared with younger adults, due to the diminished immune response. The aim of the present study is to compare the effectiveness of two influenza vaccines in reducing hospitalizations for influenza or pneumonia in the elderly and to determine which formulation is more appropriate. Methods A case-control study was performed by selecting subjects at least 65 years old from the administrative database of a Local Health Unit in Rome. The cases were hospitalized for influenza or pneumonia during influenza season in the years 2010-2011 and 2011-2012. The controls were hospitalized in the same period for different pathologies. The sample was immunized with the trivalent inactivated vaccine (TIV) in the first flu season (2010-2011) and with the adjuvanted vaccine MF59 (ATIV) in the second season (2011-2012). Results A total of 269 cases and 1247 controls were included for the 2010-2011 flu season, and 365 cases and 1227 controls for the year 2011-2012. Up to 171 (63.6%) cases and 667 (53.5%) controls in the 2010-2011 season and 287 (78.6%) cases and 786 (64.1%) controls in the 2011-2012 season have not been vaccinated. Females are less likely to be hospitalized than males especially in 2010-2011: adjusted OR (AOR) = 0.36, 95% CI = 0.21-0.64. High educational level is also a protective factor for hospitalization, especially in 2011-2012 (AOR = 0.54, 95% CI = 0.41-0.70). Subjects over 75 years were at high risk of hospitalization compared to 65-74 year olds, mostly in the second season (AOR = 1.93, 95% CI = 1.45-2.58). In subjects with 65-74 years, TIV reduces more hospitalizations (AOR = 0.49, 95% CI = 0.24-0.97) than ATIV (AOR = 0.70, 95% CI = 0.40-1.23). In those over 75 years old, ATIV is more effective (AOR = 0.43, 95% CI = 0.31-0.59) compared to TIV (AOR = 0.64, 95% CI = 0.47-0.88). Conclusions TIV and ATIV reduce hospitalization for influenza or pneumonia with a variable degree of protection in different age groups: ATIV is more effective in individuals over-75 years old. The use of ATIV in the very elderly persons would provide important clinical benefit compared to nonadjuvanted vaccines.