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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

From: Febrile seizures after 2009 influenza A (H1N1) vaccination and infection: a nationwide registry-based study

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)

  1. aAdjusted for calendar period (January–March, April–August, and September–December) and age in one-year bands
  2. 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])
  3. 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])
  4. dAll other parts of the observation period