I wasn't asked at check-in since I was travelling straight through but when I queued to get into the secure Gate F1 area at HNL, the ground agent was throughly screening the passenger ahead of me. He had printed something off the internet that didn't look very official and she was quizzing him asking for proof of immunization "within the past 2 years". Eventually she got frustrated with him and off loaded him to another agent. Mind you, this was at the onset of this about a month ago on Jan 29 so it's possible they may have changed, evolved or refined their asks.