More and more this idea, thanks to Delta, is now BULLSHIT. It's not "relatively rare". It's now more along the lines of "infrequent" or "possible".
No vaccine like this is a 100% shield, and the fact that there was little reporting on breakthroughs with previous variants, shows how earlier in the year with the vaccines slowly making headway through the population, it was "relatively rare", and was very very effective against those less aggressive strains.
But Delta has been a game-changer due to the viral load that it can apparently generate and potentially be shed...enough in fact to briefly overwhelm the body's immune system and cause symptoms that might trigger someone to get tested, and confirm either way.
It's literally been 18 months of some health officials and media locking into an "assumption", and refusing to let go until they look like fools when they keep repeating it like a broken record (like the idiotic term "herd immunity" ). 
As a sidenote, CDC apparently published their final version of the Cape Cod super-spreader - https://www.cdc.gov/mmwr/volumes/70/wr/mm7031e2.htm?s_cid=mm7031e2_w
What is sobering is that despite the attendees (and people in the state of MA) having a high, so called "herd immunity" level vaccination rate, almost 3/4 of the cases were found in vaccinated people -
The vaccine is doing its job by giving the body a head start boost to fight an infection - particularly when it comes to a variant like Delta - but it behooves to have those extra mitigation precautions to keep it bay as much as possible.
I hope Rep. Davis recovers quickly and her body mounts a robust enough response to rid her of every last bit of it.
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