Characterize Flu-like Symptoms in RRMS Patients Transitioning From IFN-B Therapies to Peginterferon Beta-1a

Key Inclusion Criteria:

- Must have a confirmed diagnosis of relapsing forms of MS, as defined by McDonald
criteria #1-4 [Polman 2005].

- Must have neurological findings consistent with an EDSS score of 0.0 - 5.0

- Must be treated with IFN-β and must be receiving a stable dose of IFN-β for at least
4 months immediately prior to screening.

- All male patients and female patients of childbearing potential must practice
effective contraception during the study and be willing and able to continue
contraception for 3 months after their last dose of study treatment.

Key Exclusion Criteria:

- Primary progressive, secondary progressive, or progressive relapsing MS [Lublin and
Reingold 1996]. These conditions require the presence of continuous clinical disease
worsening over a period of at least 3 months. Patients with these conditions may also
have superimposed relapse but are distinguished from patients with relapsing MS by
the lack of clinically stable periods or clinical improvement.

- History of severe allergic or anaphylactic reactions or known hypersensitivity to
medication which might suggest potential for a reaction to interferon beta-1a or
polyethylene glycol..

- History of malignant disease, including solid tumors and hematologic malignancies
(with the exception of basal cell and squamous cell carcinomas of the skin that have
been completely excised and are considered cured).

- History of seizure disorder or unexplained blackouts OR history of a seizure within 3
months prior to Baseline.

- Known allergy to any component of the peginterferon beta-1a formulation.

- An MS relapse that has occurred within the 50 days prior to baseline (Day 1) and/or
lack of stabilization from a previous relapse prior to baseline.

NOTE: Other protocol defined Inclusion/Exclusion criteria may apply.