Table 2.

Incidence rate ratio (IRR) estimates, with associated 95 % confidence intervals (CIs), of febrile seizure in relation to the timing of influenza vaccination and infection

Exposure	Period	No. of person-days at risk	No. of events	Incidence rate (per 100 person-days)	IRRa (95 % CI)
	Background periodd	976,010	739	0.08	1
	2 weeks before vaccination day	40,320	23	0.06	0.76 (0.50–1.43)
Vaccinationb	Day of vaccination	2880	3	0.10	1.39 (0.46–4.35)
	1–3 days after vaccination	8640	13	0.15	2.00 (1.15–3.51)
	4–7 days after vaccination	11,520	7	0.06	0.81 (0.38 – 1.73)
	Background period	95,724	63	0.07	1
	2 weeks before influenza diagnosis	3962	9	0.23	3.96 (1.81–8.65)
Influenzac	Day of influenza diagnosis	283	19	6.71	116.70 (62.81–216.90)
	1–3 days after influenza diagnosis	849	5	0.59	10.12 (3.82–26.82)
	4–7 days after influenza diagnosis	1132	1	0.09	1.50 (0.20–11.17)

^aAdjusted for calendar period (January–March, April–August, and September–December) and age in one-year bands

^bResults from self-controlled case series analysis, data from 656 Norwegian children born in 2006–2009 vaccinated with Pandemrix® and having 785 febrile seizure episodes during the total observation period (starting 180 days prior to vaccination or on day of birth [whichever came last], and ending 180 days after exposure or on the day of emigration or death [whichever came first])

^cResults from self-controlled case series analysis, data from 84 Norwegian children born in 2006–2009 diagnosed with pandemic influenza and having 97 seizures episodes during the total observation period (starting 180 days prior to vaccination or on day of birth [whichever came last], and ending 180 days after exposure or on the day of emigration or death [whichever came first])

^dAll other parts of the observation period