So this is a bit of a hot topic and tough to navigate, for me. But, I'd like to "think" that I've learned a bit from the expert folks on the forum here. I mean that.
I recently took my two pups to the vet. At two, instead of agreeing to the standard shots, I opted for Titer and blood tests. I can see why most pet owners just back down and take the booster shots and pills instead. The booster shot was way less expensive than the Titer test by a long shot.
Bottom line... No Distemper or Parvo shots needed for another two more years, and no heart worms or intestinal worms at all whatsoever. I don't want to inject or pill my pups unless I need to.