There was an early report that claimed abnormalities, but by the standards they were using just about everybody would have shown abnormalities - and they consequently did not even have a control group. Contemporary studies from 2024+ onward, using control groups, have found no physical effects or differences whatsoever. [1]

I also think it's noteworthy that claimed incidents have been reported just about everywhere, including Western nations. After the scare started, every "enemy" state individual, embassy, and other such facility would have been even more intense than usual surveillance. And absolutely no evidence of any attack of any sort whatsoever has been found.

By contrast mass psychogenic illnesses [2] have a lengthy history and their typical effects correlate identically with the typical reported effects of 'Havana Syndrome.' Actually I just noticed Havana Syndrome is now already listed as one of the examples of mass psychogenic illness. Somewhat surprising from Wiki, but accurate nonetheless.

[1] - https://jamanetwork.com/journals/jama/fullarticle/2816532

[2] - https://en.wikipedia.org/wiki/Mass_psychogenic_illness