Earlier quoted context omitted.
COVID-1970 would be a lot slower in the spread due to much less globalized world. The West probably would still not have experienced it, neither the Soviet Bloc due to then fresh Sino-Soviet split and heavily militarized border.
I think the Spanish flu might not agree with that assessment. Both plagues also did a pretty good job of spreading to pretty much all territories that had any form of contact at the time.
It also never crossed the Iron Curtain into Warsaw Pact countries.