One of employees is constantly sick

How do you guys handle managing those who get more sick days than vacation days? I manage a team of 9, including this employee who calls in sick every other week for various dubious reasons. I believe in giving everyone the benefit of the doubt and trusting in their professionalism. However, I must ensure that we are all contributing effectively to our shared goals, and the inconsistent attendance of this employee bothers me... Problem is we’re a young company and growing fast, we don't yet have a clear attendance policy. I want everyone to be productive, so sometimes when an employee asks me if they can work from home due to a stomachache or a headache, I always allow it, without any note from the doctor. As long as it doesn’t affect job performance, I’m fine with it. This guy’s performance is pretty average, and I can’t honestly say he has too much back load on his tasks. But I feel that if I allow people to stay home using all kinds of excuses, it may negatively impact the morale of the team. I mean, why go to the office when you see your other colleague keeps being absent all the time but is never asked any questions? This employee I’m concerned about has been with us for half a year, and he’s been acting like that ever since. I kind of understand that unforeseen circumstances can sometimes arise, but what to do about the frequency of his absences? I’d like to handle this in a friendly manner, for now. I’ve already sent out an email to all my team members encouraging them to reach out to me if they’re facing any challenges or need support. What should my next steps be? If you have any suggestions on how to manage this situation effectively (maintaining a positive work environment:), I'd greatly appreciate it!