Other point is ordinary contagious diseases have an incubation period of several days. Then if a magical healing effect needs a long-rest for a no-magical disease, then it shouldn't break the power balance. A different thing would be using low-level magic against magical diseased or caused by fantasy monsters.
If a poison from the real life can poison neutralized thanks to the appropriate antidote then that in D&D can by low-level healing magic, but maybe the healing would need more time, at least a short-rest.
Or spell slots are spend to "load" some potion, and this would work like the right medicine or antidote, but only with the "softer" no-magical toxins or pathogens.
Or low-level spells could be spend to craft antidotes, but with a handicap. If a Con check fails the poisoned victim is healed, but she suffers a level of exhaution until a short rest at least.
Could those healing effect break the power balance? Not if it needs a lot of time for recovery after the battle, and diseases and poisons by monsters with a higher challenge rating would need a better healing. The low-level magic wouldn't be enough.
* House rule: If a PC enjoys a medicine skill then spell slots (it doesn't matter what spell to be used) can be spent to craft no-magical medicines or antidotes. (level 0 spells can be enough but it would need more time to be crafted).
House rule 2, magical acupuncture: (smeared with ointment) magic needles can function as syringes for injuries and toxins.