Table 3.

Relationship between influenza immunization and adverse events among children 2–18 years of age with a history of asthma. Kaiser Permanente Northern California, July 1, 2007 to March 31, 2014.

Event	Group or subgroup analyzed	Risk Interval^b	Comparison interval^b	Odds Ratio (95% Confidence Interval) of adverse event in the risk interval compared to comparison interval^a		Difference-in-Differences
Event	Group or subgroup analyzed	Risk Interval^b	Comparison interval^b	IIV	LAIV	Difference-in-Differences
IP and ED asthma exacerbations	All asthma types	1–14days	29–42 days	0.97 (0.82,1.15)	0.39 (0.17,0.90)^*	0.40 (0.17,0.95)^*
	Current or recent, persistent	1–14 days	29–42 days	0.99 (0.83,1.19)	0.67 (0.21,2.17)	0.67 (0.20,2.22)
	Current or recent, not persistent	1–14 days	29–42 days	1.03 (0.62,1.71)	0.06 (0.01,0.56)^*	0.05 (0.01,0.58)^*
	Remote history of asthma only	1–14 days	29–42 days	0.63 (0.14,2.73)	0.72 (0.17,3.04)	1.14 (0.15,8.96)
	All	7–28 days	29–50 days	0.94 (0.82,1.07)	0.36 (0.17,0.78)^*	0.38 (0.17,0.84)^*
Outpatient asthma exacerbations	LAIV only, all asthma types	1–14 days	29–42 days	^c	0.75 (0.62,0.92)^*	^c
	LAIV, current or recent, persistent	1–14 days	29–42 days	^c	0.79 (0.61,1.03)	^c
	LAIV, current or recent, not persistent	1–14 days	29–42 days	^c	0.84 (0.62,1.13)	^c
	Remote history of asthma only	1–14 days	29–42 days	1.06 (0.83,1.35)	0.67 (0.39,1.16)	0.63 (0.35,1.15)
All non-asthma-related visits	All	1–14 days	29–42 days	1.06 (1.03,1.08)^*	1.05 (1.00,1.10)	0.99 (0.94,1.04)

The analytic dataset had one record per outcome. The dependent variable in the intercept-only logistic regression was “1” if the adverse event occurred during the risk window rather than the comparison window. Only one event per time window was counted. An offset term was used and was determined as follows: On the day of the event, determine the number of children at risk for the event, and who were the same age (in 1-year increments) and sex as the child with the event, and who had received the same type of influenza vaccine. Calculate the proportion of these children who were in the risk window on that day (as opposed to being in the comparison window.) This proportion divided by one minus the proportion is the odds. The logit of the odds is the offset term. For each immunization type, the odds ratio (OR) is the ratio of the odds of an event occurring in the risk interval and the odds of an event occurring in the comparison interval. The “difference-in-differences” is the ratio of the IIV odds ratio and the LAIV odds ratio. For the IIV and LAIV columns, values greater than (less than) one indicate increased (decreased) risk of the event following receipt of that vaccine. For the difference-in-differences column, values greater than (less than) one indicate that the risk of an event following LAIV is higher (lower) than the risk following IIV. IIV: inactivated influenza vaccine; LAIV: live attenuated influenza vaccine.

Intervals represent days after immunization. All events included here occurred in either the risk or comparison intervals.

Not available because chart review abstraction and confirmation was only performed for events following LAIV immunizations and for the subset of events following IIV immunization among children with remote history of asthma only.

Significant at p ≤ 0.05.