Table 2. Risk of narcolepsy ± narcolepsy associated with A/H1N1 (2009) vaccination using the cohort method according to observation period and post-vaccination risk period, in Quebec, 2009–2010.

Observation period	Risk period from dateof vaccination to:	No cases			Incidence rate			Age- and gender-adjusted risk ratio				Attributable cases/million doses(95% confidence intervals)
		E+	E−	Total	E+	E−	Total	RR	ICinf	ICsup	P-value
January 1st 2009, toDecember 31, 2010	End study periodDecember 31st, 2010	8	15	23	0.164	0.253	0.148	1.06	39.00	2.68	1.000	0.25 [−2.83 to 1.13]
	One year (365 days)post-vaccination	8	15	23	0.181	0.464	0.148	1.24	0.45	3.13	0.650	0.46 [−2.21 to 1.23]
	24 weeks (168 days)post-vaccination	7	16	23	0.344	1.039	0.148	2.73	0.95	7.04	0.063	1.04 [−0.08 to 1.36]
	16 weeks (112 days)post-vaccination*	7	16	23	0.516	1.237	0.148	4.32	1.50	11.12	0.007	1.24 [0.53 to 1.44]
	8 weeks (56 days)post-vaccination	4	19	23	0.590	0.709	0.148	4.36	1.08	13.15	0.039	0.71 [0.07 to 0.84]
May 1st 2009, toMarch 31 2010	End study periodDecember 31st, 2010	7	12	19	0.448	0.822	0.266	1.91	0.63	5.28	0.272	0.82 [−0.93 to 1.28]
	One year (365 days)post-vaccination	7	12	19	0.448	0.822	0.266	1.91	0.63	5.28	0.272	0.82 [−0.93 to 1.28]
	24 weeks (168 days)post-vaccination	7	12	19	0.448	0.822	0.266	1.91	0.63	5.28	0.272	0.82 [−0.93 to 1.28]
	16 weeks (112 days)post-vaccination	7	12	19	0.516	0.947	0.266	2.33	0.77	6.43	0.138	0.95 [−0.47 to 1.34]
	8 weeks (56 days)post-vaccination	4	15	19	0.590	0.549	0.266	2.39	0.58	7.52	0.233	0.55 [−0.66 to 0.78]
October 4 2009, toMarch 31 2010	End study periodDecember 31st, 2010	7	3	10	0.448	0.133	0.262	2.73	0.62	16.45	0.234	1.11 [−0.97 to 1.49]
	One year (365 days)post-vaccination	7	3	10	0.448	0.133	0.262	2.73	0.62	16.45	0.234	1.11 [−0.97 to 1.49]
	24 weeks (168 days)post-vaccination	7	3	10	0.448	0.133	0.262	2.73	0.62	16.45	0.234	1.11 [−0.97 to 1.49]
	16 weeks (112 days)post-vaccination	7	3	10	0.516	0.122	0.262	3.63	0.82	21.82	0.098	1.21 [−0.35 to 1.51]
	8 weeks (56 days)post-vaccination	4	6	10	0.590	0.191	0.262	2.73	0.57	11.55	0.229	0.61 [−0.68 to 0.83]

+: Cases with onset after vaccination during risk period; E−: Cases not vaccinated or with onset before vaccination or after end of risk period.

*Primary analysis defined a priori.