Table 1.

Population incidence rate of narcolepsy diagnosis (first-ever narcolepsy ICD-9 diagnosis code in a patient’s record) by pandemic and non-pandemic time periods in the Vaccine Safety Datalink population, 2006–2011

Age Group:	<10 years old			10–19 years old			20–29 years old
Time Period	n	IR*	IRR (95%CI)	n	IR*	IRR (95%CI)	n	IR*	IRR (95%CI)
Jan 2006 – Mar 20091	26	0.79	reference	160	3.99	reference	366	11.63	reference
Apr 2009 – Sep 20092	7	1.36	1.72 (0.69–3.83)	20	3.22	0.81 (0.49–1.26)	64	13.05	1.12 (0.86–1.46)
Oct 2009 – Dec 20113	18	0.78	0.99 (0.53–1.80)	128	4.61	1.16 (0.92–1.46)	256	11.25	0.97 (0.82–1.13)
Apr 2009 – Dec 20114	25	0.88	1.12 (0.64–1.95)	148	4.35	1.09 (0.87–1.37)	320	11.57	0.99 (0.86–1.16)

Abbreviations: CI = confidence interval; IR = incidence rate; IRR = incidence rate ratio.

^*Incidence rate is expressed per 100,000 person years

¹Prepandemic

²Pandemic, before vaccine available

³After pandemic vaccine available

⁴All pandemic and post-pandemic time included in the study