Even though I agree with Lothor that you shouldn't really quantify the verb "stop", in this case the nuance is "to bring to an end" or "lessen", which I would say would be quantifiable. Also I would say "to further stop the spread" and "to stop the spread further" are different in meaning to "to stop the further spread". In the first two sentences you are saying this action has been taken in addition to other ones in order to lessen the spread of the virus even more, as "further" is qualifying "stop", whereas the latter sentence sounds like the virus is spreading further, as "further" is qualifying "spread", but that would be inaccurate as the rate of infection is on a steady decline.