Influenza vaccine effectiveness in preventing inpatient and outpatient cases in a season dominated by vaccine-matched influenza B virus

Figures & data

Figure 1. Number of influenza cases and test-negative controls, and incidence of influenza-like illness by week, 2012–2013 season in Navarra, Spain.

Table 1. Baseline characteristics of laboratory-confirmed influenza cases and test-negative controls, 2012–2013 influenza season in Navarra, Spain

	All influenza cases	Test-negative controls		Influenza B cases	Test-negative controls
	N (%)	N (%)	p-Value	N (%)	N (%)	p-Value
Age groups (in years)			<0.001			<0.001
<5	17 (5)	46 (13)		15 (5)	42 (13)
5–14	88 (23)	61 (17)		69 (26)	58 (18)
15–44	158 (41)	116 (32)		102 (38)	106 (32)
45–64	92 (24)	72 (20)		61 (23)	63 (19)
≥65	27 (7)	67 (18)		21 (8)	60 (18)
Sex			0.865			0.859
Male	196 (51)	188 (52)		138 (51)	167 (51)
Female	186 (49)	174 (48)		130 (49)	162 (49)
Residence			0.150			0.148
Rural	104 (27)	116 (32)		71 (27)	105 (32)
Urban	278 (73)	246 (68)		197 (73)	224 (68)
Migrant status			0.452			0.952
No	342 (90)	330 (91)		244 (91)	300 (91)
Yes	40 (10)	32 (9)		24 (9)	29 (9)
Major chronic conditions			<0.001			0.001
No	269 (70)	209 (58)		185 (69)	184 (56)
Yes	113 (30)	153 (42)		83 (31)	145 (44)
Target population for vaccination			<0.001			0.001
No	253 (66)	186 (51)		173 (65)	166 (51)
Yes	129 (34)	176 (49)		95 (35)	163 (49)
Health care setting			<0.001			<0.001
Hospital	53 (14)	133 (37)		32 (12)	114 (35)
Primary health care	317 (83)	205 (57)		231 (86)	194 (59)
Emergency room	12 (3)	24 (6)		5 (2)	21 (6)
Seasonal influenza vaccine 2012–2013			<0.001			<0.001
No	357 (93)	278 (77)		252 (94)	255 (78)
Yes	25 (7)	84 (23)		16 (6)	74 (22)
TOTAL	382 (100)	362 (100)		268 (100)	329 (100)

^a Cases and controls included in the analysis between week 50 of 2012 and week 19 of 2013.

^b Influenza B cases and controls included in the analysis between week 50 of 2012 and week 15 of 2013.

^c Chi-square test.

^d Target population for vaccination includes people aged ≥60 years and people with major chronic conditions.

Table 2. Distribution by type/subtype and strain of influenza cases with genetic characterization during the 2012–2013 season in Navarra, Spain

	Total	Influenza A(H1N1)pdm09	Influenza A(H3N2)	Influenza B
Virus strains	N (%)	N (%)	N (%)	N (%)
A/StPetersburg/27/2011(nH1N1)	26 (20)	26 (79)
A/StPetersburg/100/2011(nH1N1)	7 (5)	7 (21)
A/Victoria/361/2011(H3N2)	17 (13)		17 (100)
B/Estonia/55669/2011(Yamagata)	39 (30)			39 (49)
B/Wisconsin/1/2010(Yamagata)	34 (26)			34 (43)
B/Brisbane/60/2008(Victoria)	6 (5)			6 (8)
Total	129 (100)	33 (100)	17 (100)	79 (100)

Table 3. Influenza vaccine effectiveness in preventing laboratory-confirmed influenza in the 2012–2013 influenza season in Navarra, Spain

	Cases/controls	Crude vaccine effectiveness, % (CI 95%)	Adjusted vaccine effectiveness, % (CI 95%)	p-Value
All swabbed patients
Unvaccinated	357/278	1	1
Vaccinated	25/84	77 (63 to 86)	63 (34 to 79)	0.001
Age <65 years
Unvaccinated	341/258	1	1
Vaccinated	14/37	71 (46 to 85)	59 (17 to 80)	0.013
Age ≥65 years
Unvaccinated	16/20	1	1
Vaccinated	11/47	71 (26 to 88)	75 (22 to 92)	0.017
Target population for vaccination
Unvaccinated	109/103	1	1
Vaccinated	20/73	74 (54 to 85)	67 (36 to 83)	0.001
Primary health care patients
Unvaccinated	303/182	1	1
Vaccinated	14/23	63 (27 to 82)	55 (1 to 80)	0.048
Hospitalized patients
Unvaccinated	42/78	1	1
Vaccinated	11/55	63 (21 to 82)	74 (33 to 90)	0.005
Influenza A cases vs. controls
Unvaccinated	105/251	1	1
Vaccinated	9/77	72 (42 to 86)	43 (−45 to 78)	0.236
Influenza A(H3N2) cases vs. controls
Unvaccinated	17/207	1	1
Vaccinated	2/64	62 (−69 to 91)	68 (−89 to 95)	0.220
Influenza A(H1N1)pdm09 cases vs. controls
Unvaccinated	88/247	1	1
Vaccinated	5/73	81 (51 to 92)	50 (−57 to 84)	0.236

CI: Confidence interval.

^a Vaccine effectiveness adjusted for sex, age group (<5, 5–14, 15–44, 45–64 and ≥65 years), month of sample collection, major chronic conditions and healthcare setting (primary healthcare, hospitalization and emergency room).

^b Target population for vaccination includes people aged ≥60 years and people with major chronic conditions.

^c The analysis of influenza A(H3N2) cases was restricted to weeks 2 to 14 of 2013. One case of influenza A(H3N2) in week 17 was excluded.

^d The analysis of influenza A(H1N1)pdm09 cases was restricted to weeks 1 to 17 of 2013.

Table 4. Influenza vaccine effectiveness in preventing influenza B cases in Navarra, Spain, week 50 of 2012 to week 15 of 2013

	Influenza B cases/controls	Crude vaccine effectiveness, % (CI 95%)	Adjusted vaccine effectiveness, % (CI 95%)	p-Value
All influenza B cases
Unvaccinated	252/255	1	1
Vaccinated	16/74	78 (61 to 88)	70 (41 to 85)	0.001
Age <65 years
Unvaccinated	237/237	1	1
Vaccinated	10/32	69 (35 to 85)	59 (6 to 82)	0.035
Age ≥65 years
Unvaccinated	15/18	1	1
Vaccinated	6/42	83 (49 to 94)	89 (53 to 97)	0.003
Target population for vaccination
Unvaccinated	81/96	1	1
Vaccinated	14/67	75 (53 to 87)	70 (37 to 86)	0.002
Primary health care patients
Unvaccinated	220/174	1	1
Vaccinated	11/20	56 (7 to 80)	56 (−5 to 81)	0.065
Hospitalized patients
Unvaccinated	27/66	1	1
Vaccinated	5/48	74 (29 to 91)	87 (52 to 96)	0.002

CI: Confidence interval.

^a Vaccine effectiveness adjusted for sex, age group (<5, 5–14, 15–44, 45–64 and ≥65 years), month of sample collection, major chronic conditions and healthcare setting (primary healthcare, hospitalization and emergency room).

^b Target population for vaccination includes people aged ≥60 years and people with major chronic conditions.

Table 5. Effectiveness of the influenza seasonal vaccines received in the current and previous seasons against influenza B cases in Navarra, Spain, week 50 of 2012 to week 15 of 2013

	Influenza B cases/controls	Adjusted vaccine effectiveness, % (CI 95%)	p-Value
Seasonal influenza vaccine 2012–2013
Unvaccinated	252/255	1
Vaccinated	16/74	69 (23 to 88)	0.012
Seasonal influenza vaccine 2008–2009
Unvaccinated	254/273	1
Vaccinated	14/56	25 (−97 to 71)	0.556
Seasonal influenza vaccine 2009–2010, 2010–2011 or 2011–2012
Unvaccinated	241/244	1
Vaccinated	27/85	−18 (−172 to 49)	0.698

CI: Confidence interval.

^a Vaccine effectiveness adjusted for sex, age group (<5, 5–14, 15–44, 45–64 and ≥65 years), month of sample collection, major chronic conditions, healthcare setting (primary healthcare, hospitalization and emergency room) and by the variables included in the table.

^b Vaccines in seasons 2008–2009 and 2012–2013 included Yamagata lineage. Vaccines in seasons 2009–2010, 2010–2011 and 2011–2012 included Victoria lineage.