No one has the idea, nobody knows. One can say how many scanstrings are in the NOD32 databases, but it is impossible to say, how many viruses and worms NOD can detect. Due the NOD32 advanced heuristic analysis it detects also the viruses and worms only to be written. Anyway saying antivirus XY detect this number and YX that number of viruses/worms/trojans is information without value. One antivirus can catch virus.a, virus.ba, virus.df but for other antivirus all the three are the same VIRUS.A.... Numbers of detected viruses are good more or less just for marketing....It depends on the scanning engine how viruses are handled. There can be an antivirus which needs 10 scanstrings to catch one particular virus as well as it can be antivirus which catches 10 viruses with one scanstring Anyway, you can guess the number of scanstrings Hint: look are in ten of thousands range. Correct guess will be avarded by a bottle of beer.....
Nod seems OK but Invircible is the smart one. It stamps every folder and at every startup, it asks you if the new exe it found is authentic and asks you if it can or should delete it. Invircible also creates a live bait for unknown virus which is an exe that Invircible renames every sixty seconds. It was the only antivirus that solved my problems when it suggested that some PE files might be a virus. They were indeed. SO, even if Invircible does not know the virus, it has a fair chance of finding brand new unknown virii (plural).
Hmm, well maybe it is all not that good: http://www.pc-help.org/www.nwinternet.com/pchelp/lockdown/Davis/Paris.htm