I assume you are communicating only among the programs that waitlisted you... not to a school where you have the CTE deadline.
I agree, if there is a direct communication portal to the admissions team, I would send the message. (I'm sure email is fine too.) However, the other school is in no rush to act on your disclosure. Some may say, "we're still full. Have fun at the other school... see you at your residency interviews!"
See our article on Letters of Intent.
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