Table 2:

Unadjusted and adjusted^* relative risk of seizure following MMRV and MMR+V vaccination, relative to baseline risk over 42 days before vaccination, and relative risk ratio for full cohort and by risk group

Postvaccine period	MMRV		MMR+V		RR ratio, MMRV to MMR+V
	Unadjusted RR (95% CI)	Adjusted RR (95% CI)	Unadjusted RR (95% CI)	Adjusted RR (95% CI)	Unadjusted (95% CI)	Adjusted (95% CI)
Full cohort (n = 277 774)
Days 0 to 42	1.94 (1.67–2.26)	1.80 (1.43–2.27)	1.33 (1.16–1.54)	1.48 (1.22–1.79)	1.45 (1.25–1.70)	1.21 (0.93–1.58)
Days 7 to 10	9.15 (7.49–11.18)	6.57 (4.77–9.05)	3.79 (3.04–4.73)	3.30 (2.40–4.52)	2.41 (1.85–3.15)	1.99 (1.30–3.05)
Low-risk group (n = 266 768)
Days 7 to 10	10.86 (8.71–13.53)	6.69 (4.90–9.13)	3.90 (3.02–5.04)	2.94 (2.13–4.07)	2.78 (2.07–3.75)	2.27 (1.48–3.49)
High-risk group† (n =11 006)
Days 7 to 10	4.30 (2.58–7.16)	4.68 (2.49–8.79)	3.63 (2.33–5.64)	3.61 (2.20–5.93)	1.19 (0.64–2.21)	1.30 (0.60–2.79)

Note: CI = confidence interval, MMRV = measles–mumps–rubella–varicella vaccine, MMR+V = measles–mumps–rubella vaccine plus varicella vaccine, RR = relative risk. ^*Adjusted for calendar year and age.

^†Only 4 cases of postvaccination seizure were identified in the high-risk group in 2011, lower than expected given that about 10 cases were identified in each of the other years. Thus, 2011 was treated as an outlier but was kept in the model by including a separate parameter for this year and its effect on the high-risk group within the risk interval.