Hi, Mary. Neither “social media” nor “public health” would typically need to be hyphenated in that context (both are well-established open compounds rather than novel compound modifiers, and hyphenation wouldn’t be necessary for clarity). It terms of the comma, you only need a comma between adjectives when they are coordinate (i.e., when they modify a word in the same way). I don’t think that is really the case here (assuming “social media” refers to the type of platform and “public health” refers to its purpose or focus). But this may depend on how you are using the term. A helpful test for whether adjectives are coordinate is to try placing “and” between them, so if “a social media and public health platform” sounds like a good description of what you’re trying to communicate, then “social media, public health platform” would be correct. If the “and” sounds out of place, then “social media public health platform” may be more appropriate.

Typo now fixed. Thanks, Racquel.