I think if Avonex is your thing, you would have settled to it already. Lasting side effects rarely fade completely; once a 'flu' sufferer, always a 'flu' sufferer I tend to think.
A year of suffering on Beta was enough for me. it was never going to get better.
Switched to C over a year ago.
Follow up MRI tomorrow 2 year update (hence up late tonight worrying as one does).
Will update on if they think the C is working. Cross fingers...