Effectiveness of 2012–2013 influenza vaccine against influenza-like illness in general population

Figures & data

Figure 1. Design of the cohort.

Figure 2. Flowchart of the study.

Table 1. Baseline characteristics of all GrippeNet.fr included participants, depending on their vaccination status

	Vaccinated individuals % (number)	Unvaccinated individuals % (number)	Overall % (number)	P value
Socio-demographic factors
Gender (women)	55% (359)	65% (873)	62% (1232)	<10^−3
Age:				<10^−3
0–49*	21% (140)	41% (553)	35% (693)
50–64	31% (203)	40% (530)	37% (733)
≥65	48% (314)	19% (256)	28% (570)
Presence of a child (under five years) in the household	7% (46)	14% (182)	11% (228)	<10^−3
Health factors
To take regular medication for asthma	8% (51)	4% (53)	5% (104)	<10^−3
To take regular medication for a lung disorder	4% (25)	1% (13)	2% (38)	<10^−3
To take regular medication for diabetes, a heart disorder, kidney disorder or an immunocompromising condition	23% (151)	9% (125)	14% (276)	<10^−3
Frequency of cold/flu:				0.32
- Less than one per year	48% (319)	45% (602)	46% (921)
- One or two per year	37% (241)	39% (523)	38% (764)
- At least three per year	15% (97)	16% (214)	16% (311)
Dependent variable
To have at least one ILI during the epidemic period	7% (43)	13% (170)	11% (213)	<10^−3
Total	33% (657)	67% (1339)	100% (1996)

*One child under 5 y.

Table 2. The crude and adjusted IVE estimates of the 2012–2013 seasonal vaccine of GrippeNet.fr participants reporting an ILI defined by the presence of fever ≥38 °C and cough (significant results appear in bold)

	Crude OR (95% CI)	Adjusted OR (95% CI)	Corrected OR (95% CI)	P value (multivariate analysis, analysis of deviance)
Vaccination
Influenza vaccination during the current season	0.38 (0.24 to 0.60)	0.49 (0.31 to 0.79)	0.51 (0.33 to 0.80)	<10^−3
Socio-demographic factors
Gender (women)	0.99 (0.67 to 1.46)	1.09 (0.74 to 1.61)	1.07 (0.77 to 1.47)	0.51
Age:
0–49	1	1	1	0.045
50–64	0.36 (0.25 to 0.52)	0.60 (0.39 to 0.92)	0.62 (0.41 to 0.93)
≥65	0.34 (0.22 to 0.53)	0.77 (0.45 to 1.32)	0.78 (0.47 to 1.29)
Presence of a child (under five years) in the household	3.43 (2.23 to 5.30)	2.24 (1.39 to 3.61)	1.61 (1.24 to 1.97)	<10^−3
Health factors
To take regular medication for asthma	1.66 (0.76 to 3.63)	1.69 (0.71 to 4.02)	1.46 (0.76 to 2.36)	0.051*
To take regular medication for a lung disorder	0.59 (0.17 to 2.01)	0.60 (0.12 to 3.10)	0.63 (0.13 to 2.56)	0.41
To take regular medication for diabetes, a heart disorder, kidney disorder or an immunocompromising condition	0.67 (0.37 to 1.21)	1.30 (0.72 to 2.36)	1.26 (0.74 to 2.04)	0.32
Frequency of cold/flu:
- Less than one per year	1	1	1	<10^−3
- One or two per year	1.78 (1.13 to 2.80)	1.49 (0.93 to 2.38)	1.39 (0.94 to 1.98)
- At least three per year	4.17 (2.56 to 6.78)	2.75 (1.63 to 4.63)	1.83 (1.38 to 2.28)

*P value of the Wald test = 0.24

Table 3. The IVE estimates of the 2012–2013 seasonal vaccine evaluated in GrippeNet.fr sub-populations at risk for severe influenza reporting an ILI defined by the presence of fever ≥38 °C and cough

	Overall at-risk population	Individuals ≥65	At-risk population <65	Individuals who have consulted a MG during the season
Number of included individuals (vaccinated; unvaccinated)	807 (429; 378)	570 (314; 256)	237 (115; 122)	574 (171; 403)
IVE (95% CI)	34% (0 to 60)	29% (0 to 63)	40% (0 to 73)	40% (0 to 67)
P value (analysis of deviance)	0.10	0.30	0.21	0.048*
Corrected IVE (95% CI)	32% (0 to 58)	28% (0 to 61)	37% (0 to 71)	35% (0 to 62)
Attack rate for unvaccinated individuals (number of ILI)	12% (44)	9% (22)	18% (22)	27% (107)
Attack rate for vaccinated individuals (number of ILI)	7% (32)	6% (20)	10% (12)	18% (31)

* P value of the Wald-test = 0.083

Table 4. The IVE estimates of the 2012–2013 seasonal vaccine evaluated considering several ILI definitions

	Main analysis (cough + fever ≥38 °C)	French Sentinelles network definition^⊥	ECDC definition^γ
Number of included individuals (vaccinated; unvaccinated)	1996 (657; 1339)	1996 (657; 1339)	1996 (657; 1339)
IVE (95% CI)	51% (21 to 69)	45% (0 to 82)	26% (0 to 45)
P value (analysis of deviance)	<10^−3	0.094	0.021*
Corrected IVE (95% CI)	49% (20 to 67)	45% (0 to 82)	21% (0 to 38)
Attack rate for unvaccinated individuals (number of ILI)	13% (170)	3% (42)	33% (438)
Attack rate for vaccinated individuals (number of ILI)	7% (43)	1% (7)	23% (154)

^⊥a sudden fever >39 °C (102 °F) with myalgia and respiratory signs. ^γacute onset of reported symptoms and at least one of four systemic symptoms (fever/chills, feeling tired/exhausted, headache, muscle pain) and at least one of three respiratory symptoms (cough, sore throat, shortness of breath) . *P value of the Wald test = 0.050.