I wouldn’t use the number of sick days as some form of “national health metric” since there’s probably a bunch of factors that influence it as much (if not more) than actual sickness, like for example: how many sick days are you actually allowed to take, how much do you get paid on sick days, what’s the culture around taking sick days?

If you want to measure general health, you could go for example for life expectancy. Or if you care about the healthcare system itself you could go for infant/maternal mortality. Or if you want to measure efficiency you could go for spending per capita.