Table 3.

Incidence of treatment-emergent antipeginterferon beta1a NAbs at year 1 and over 2 years^a.

	Year 1			Over 2 years
	Placebo (n = 489)	Peginterferon beta1a	Peginterferon beta1a	Peginterferon beta1a	Peginterferon beta1a
		every 2 weeks (n = 491)	every 4 weeks (n = 492)	every 2 weeks (n = 715)	every 4 weeks (n = 716)
Patients with ⩾1 positive antipeginterferon beta1a NAbs result, n (%)b	2 (<1)	4 (<1)	2 (<1)	7 (<1)	6 (<1)
Transient positive, n (%)c	1 (<1)	2 (<1)	2 (<1)	2 (<1)	5 (<1)
Persistent positive, n (%)c	1 (<1)	2 (<1)	0	5 (<1)	1 (<1)
Low titer, n (%)	1 (<1)	3 (<1)	1 (<1)	2 (<1)	3 (<1)
Medium titer, n (%)	1 (<1)	1 (<1)	1 (<1)	3 (<1)	3 (<1)
High titer, n (%)	0	0	0	1 (<1)	0

^aAll patients who received peginterferon beta1a at any point during the study.

^bNAb assay was performed only in anti-IFN BAb-positive samples, per tiered assay design; percentages are given as a proportion of the total number of patients at risk (the number of patients whose baseline antibody was not positive and who had at least one post-baseline immunogenicity assessment).

^cTransient positive defined as a single positive evaluation, or more than one positive evaluation occurring less than 74 days apart; persistent positive defined as at least two consecutive positive evaluations that occurred at least 74 days apart or a positive evaluation at the final assessment. Results reported as ‘positive titer not determinable’ were considered titer missing. Antipeginterferon NAbs titer levels: low (⩽50), medium (>50 and ⩽700), or high (>700).

BAb, binding antibody; IFN, interferon; NAb, neutralizing antibody.