Trends of influenza B during the 2010–2016 seasons in 2 regions of north and south Italy: The impact of the vaccine mismatch on influenza immunisation strategy

Figures & data

Figure 1. Prevalence of confirmed influenza A and B infections between 2010 and 2016, according to annual epidemic.

Table 1. Number of specimens tested, influenza cases, and relative percentages attributable to influenza A and B virus subtypes. Period: 2010-2016.

Influenza season	ILI incidence rate (x 1,000)^*	Number of specimens tested	Influenza cases	Influenza A	Influenza B
Total [n (%), % by row]		14,212	1,874 (13.2)	1,315 (70.2)	559 (29.8)
2010-2011	11.1	2,228	273 (12.2)	210 (76.9)	63 (23.1)
2011-2012	9.6	1,658	192 (11.6)	192 (100.0)	0
2012-2013	10.0	1,961	227 (11.6)	73 (32.2)	154 (67.8)
2013-2014	6.6	2,234	162 (7.2)	159 (98.1)	3 (1.9)
2014-2015	10.9	2,705	335 (12.4)	270 (80.6)	65 (19.4)
2015-2016	6.1	3,426	685 (20.0)	411 (60.0)	274 (40.0)

* National influenza-like illness (ILI) incidence rate at the epidemic peak. Source: InfluNet, influenza sentinel surveillance network, Italy.

Table 2. Age distribution of influenza B infections, according to community and hospital settings. Period: 2010-2016.

	Influenza B infections
	Total [n (%)]	Community-based [n (%)]	Hospital-based [n (%)]
	559	422 (75.5)	137 (24.5)
Age (years) [median (IQR)]	9.0 (33)	8.0 (8)^*	51.0 (48)^*
Age groups (years) [n (%), % by column]
≤4	98 (17.5)	85 (20.1)	13 (9.5)
5–9	182 (32.6)	172 (40.8)	10 (7.3)
10–14	66 (11.8)	61 (14.4)	5 (3.6)
15–19	24 (4.3)	21 (5.0)	3 (2.2)
20–34	38 (6.8)	23 (5.4)	15 (11.0)
35–49	46 (8.2)	26 (6.2)	20 (14.7)
50–64	46 (8.2)	18 (4.3)	28 (20.4)
65–85	53 (9.5)	15 (3.6)	38 (27.7)
>85	6 (1.1)	1 (0.2)	5 (3.6)

* p < 0.001

Table 3. Proportion of influenza B infections, according to viral lineage (pooled data from Liguria and Sicily). Period 2010-2016.

	Victoria-lineage	Yamagata-lineage
Influenza B infections [n (%), % by row], n = 498	298 (59.8)	200 (40.2)
Age (years) [median (IQR)]	8.0 (9.0)^*	12.0 (40.0)^*
Age groups (years) [n (%), % by column]
≤4	57 (19.1)	32 (16.0)
5–9	124 (41.6)	54 (27.0)
10–14	44 (14.8)	20 (10.0)
15–19	13 (4.3)	10 (5.0)
20–34	20 (6.7)	11 (5.5)
35–49	10 (3.4)	27 (13.5)
50–64	10 (3.4)	25 (12.5)
65–85	20 (6.7)	15 (7.5)
>85	0	6 (3.0)
Influenza season [n (%), % by row]
2010-2011	27 (77.1)	8 (22.9)
2011-2012	0	0
2012-2013	5 (3.9)	122 (96.1)
2013-2014	0	1 (100.0)
2014-2015	0	62 (100.0)
2015-2016	266 (97.4)	7 (2.6)
Healthcare settings [n (%), % by row]^**
Community-based	269 (63.9)	152 (36.1)
Hospital-based	29 (37.7)	48 (62.3)

* p < 0.001

** OR=2.95 (95%CI: 1.78 - 4.67). Hospital-based setting as reference group.

Figure 2. Relative frequencies of lineage-level matched and mismatched influenza B virus infections identified between 2010 and 2016, compared with the vaccine strain for the Northern Hemisphere and according to annual epidemic (pooled data from Liguria and Sicily).