We estimated the seasonal influenza vaccine effectiveness (VE) as 1 minus the OR, expressed as a percentage. Among the 773 eligible children, 69 (9%) were excluded (Fig. 1). The main reason for exclusion was lack of informed consent either to collect the nasopharyngeal swab (n = 25) or to be included in the study (n = 10). ABT-263 chemical structure The 704 remaining children were classified as cases (262 children tested positive for one of the influenza viruses) and controls (442 children who tested negative). The percentage of hospitalised children was 56% (n = 148)

among cases and 75% (n = 332) among controls. Overall, the age of the enrolled children ranged from 6 months to 16 years. The proportion of cases ranged from 12% to 56% in the 11 centres. In 69% of cases and 55% of controls the test was performed the same day of symptom onset. In 97% of cases and in 93% of controls the test was carried out within 2 days. Among cases, B virus was detected in 126 children (48%), A(H1N1) in 59 (23%), unspecified A virus in 33 (13%), A(H1N1)pdm09 in 22 (8%) and A(H3N2) in 22 (8%). In the 2012–2013 season the virology unit of one clinical centre was able to characterise 40 of the 126 cases positive for influenza B selleck inhibitor virus: they all resulted belonging to B/Yamagata/16/88 lineage. Cases and controls were similar with regard to gender and prevalence of chronic diseases, whereas a statistically significant

difference was observed for age (46 months in cases and 29 months in controls) (Table 1). The median duration of symptoms before the visit to the ED was similar in the two groups (3 days vs. 2), as it was the

level of fever (median of 39 °C in both groups). According to the ILI definition all children many presented fever ≥38 °C. Cough was the most frequently associated symptom in both cases and controls (85% vs. 83%), followed by rhinorrhea, malaise, sore throat and asthenia. Vomiting or diarrhoea were more frequently reported in younger children (40% in patients up to 5 years and 21% in older ones). Sixty-eight percent of children were hospitalised through the EDs and the mean duration of hospitalisation was not statistically different in cases and controls (3.6 and 4.3 days respectively). Only 25 children (4%) were vaccinated against influenza: seven of the 262 cases and 18 of the 442 controls (they had been vaccinated between October and mid-January). The date of vaccination was not available for six children (one case and five controls). However, it is likely that these children were vaccinated at least 14 days before hospital admission, since they were hospitalised between the end of January and February. Twelve out of the 25 vaccinated children (46%) reported a chronic disease (asthma, allergy, cardiomyopathy, spinal muscular atrophy [SMA 1 or 2], immunodeficiency, aplastic anaemia, coeliac disease, West syndrome). The overall age-adjusted VE was 38% (95% CI: −52% to 75%) (Table 2).