Influenza epidemiology in Italy two years after the 2009-2010 pandemic: Need to improve vaccination coverage

Since 2000, a sentinel surveillance of influenza, INFLUNET, exists in Italy. It is coordinated by the Ministry of Health and is divided into two parts; one of these is coordinated by the National Institute of Health (NIH), the other by the Inter-University Centre for Research on Influenza and other Transmissible Infections (CIRI-IT). The influenza surveillance system performs its activity from the 42nd week of each year (mid-October) to the 17th week of the following year (late April). Only during the pandemic season (2009/2010) did surveillance continue uninterruptedly. Sentinel physicians - about 1,200 general practitioners and independent pediatricians - send in weekly reports of cases of influenza-like illness (ILI) among their patients (over 2% of the population of Italy) to these centers. In order to estimate the burden of pandemic and seasonal influenza, we examined the epidemiological data collected over the last 3 seasons (2009-2012). On the basis of the incidences of ILIs at different ages, we estimated that: 4,882,415; 5,519,917; and 4,660,601 cases occurred in Italy in 2009-2010, 2010-2011 and 2011-2012, respectively. Considering the ILIs, the most part of cases occurred in < 14 y old subjects and especially in 5-14 y old individuals, about 30% and 21% of cases respectively during 2009-2010 and 2010-2011 influenza seasons. In 2011-2012, our evaluation was of about 4.7 million of cases, and as in the previous season, the peak of cases regarded subjects < 14 y (about 29%). A/California/07/09 predominated in 2009-2010 and continued to circulate in 2010-2011. During 2010-2011 B/Brisbane/ 60/08 like viruses circulated and A/H3N2 influenza type was sporadically present. H3N2 (A/Perth/16/2009 and A/ Victoria/361/2011) was the predominant influenza type-A virus that caused illness in the 2011-2012 season. Many strains of influenza viruses were present in the epidemiological scenario in 2009-2012. In the period 2009-2012, overall vaccination coverage was low, never exceeding 20% of the Italian population. Among the elderly, coverage rates grew from 40% in 1999 to almost 70% in 2005-2006, but subsequently decreased, in spite of the pandemic; this trend reveals a slight, though constant, decline in compliance with vaccination. Our data confirm that 2009 pandemics had had a spread particularly important in infants and schoolchildren, and this fact supports the strategy to vaccinate schoolchildren at least until 14 y of age. Furthermore, the low levels of vaccination coverage in Italy reveal the need to improve the catch-up of at-risk subjects during annual influenza vaccination campaigns, and, if possible, to extend free vaccination to at least all 50-64-y-old subjects. Virologic and epidemiological surveillance remains critical for detection of evolving influenza viruses and to monitor the health and economic burden in all age class annually.