Sorry to hear about your loss. I did do some checking and according to this web site TLC Animal Hospital: and the linked story:

the puppy’s immune system did not respond to the vaccine (this is caused by a genetic anomaly and is primarily found in Pit Bulls, Rottweilers, Doberman Pinschers, and Labradors, though any breed of dog may be affected)

Some times it is just the luck of the draw. make sure to clean the area he primarily slept and pooped and peed real good. Evidently the parvo virus can live for a long time.