There still is the possibility that viruses play an important role in the etiopathogenesis of MS. Therefore, a randomised, double-blind study of acyclovir, an agent commonly used for the treatment of herpes simplex infections, was performed. 60 patients with RRMS were treated with acyclovir 800 mg three times a day or placebo. A 34 percent reduction in the annual relapse rate was reported during active treatment, warranting further research of acyclovir and related agents. A recent trial of valacyclovir failed to demonstrate benefit in RRMS.

In the opinion of the Committee, the rationale behind antiviral therapy is partly plausible, but it has not been extensively tested so far, and therefore must be regarded as experimental.