There is a lot of room for interpretation here. Without many guidelines this question can do so many ways so I will do my best to answer.
A state can make sure it’s citizens are healthy with a ready supply of medical supplies. Without the supplies the medical field would be undersupplied and unable to accurately or quickly complete its job.
Readily available healthcare is also important for healthy citizens. If your citizens can’t afford treatment or can’t safely afford treatment they will opt to not have it, therefore remain unhealthy for longer. A healthy economy also plays into this so the citizens can afford the healthcare and treatments.
Legislation on requiring “sick days” at work would allow for more healthy citizens as well. If a worker is sick but still has to attend work, so they can live, they will likely infect others. That would only increase the amount of sick people though.
Education on sickness and how it affects yourself and others. Those who are educated are less likely to put others in danger, especially in reference to preventable sicknesses.
All of those options, and many more as it is a broad topic, can allow a state to control the amount of unhealthy citizens. If citizens can afford to, and are educated enough to, stay healthy they will.