Clinics are welfare & media buildings in Tropico 5. They provide basic healthcare to the island, which makes them important to build early in the World Wars era. They don't exist in the Colonial Era, probably because the fields of pharmacology and surgery were weak until doctors could rely on proper anesthesia and adequate germ-reduction practices, again something that we strove towards in the Industrial Age. Also, as mentioned in the Tropico 5 Travel Guide, Tropicans love to eat corn and "...corn is very healthy and keeps you slim. Tastes especially good with fried chicken..." so they basically don't need healthcare in the Colonial Era.