Well avast 4.8 has been its death throws for some considerable time as far as support goes. So the virus definitions are going to be an issue as there are two update streams 4.8 and the remainder of avast versions, 5, 6, 7 & 8.
I don't know if the 4.8 definition updates have now ended, if not it won't be long, so this is no long term solution.
Rather depends on what your definition of adequate protection is, things have moved on a great deal since avast 4.8 not just in terms of the AV but also malware and detections.