He's right though, infection isn't really an issue. You either die before you reach 100%, intentional or not, or you use medicine from your stockpile of supplies.
I had thought a bit about this, there a couple ways to handle this:
make medicine harder to come by
add some extra penalty for dying while infected beyond a certain limit
increased xp penalty
spawn infected, with rate reset
have zombies hits have chance raise infection rate if already infected
more reasons to use medicines
more dangerous early infection
1 is about limiting the supply of medicine. It's a bit clumsy and is hard to balance properly and is still a non issue with crafting late game.
2 is more about preventing a player from ignoring the mechanic by getting themself killed before it's an issue. The problem with this is if you were to die by zombies there's a good chance you go infected along the way, so you'd have to limit the penalty to only players above a certain infection rate (25%, 50%?) so that is only affects those that ignored infection
3 is more about making infection rise quicker and forcing the user to consume more medicine. Best part about this one is that the mechanic for chance to infect is already there, just needs some modifying. You'd have to cap the effect so you don't die from successive hits even if you have the health. Could be 1% increase for each hit chance capping at maybe 30%
4 is about reducing supply. Example of this would be a food recipes for honey and requiring antibiotics to be used in first aid crafting(probably give first aid kits 10% infection rate reduction)
5 is about making infection always have a downside, stage 1 has no downsides currently. Introducing a debuff like 10% reduced stamina cap or 15% less effectiveness from food and drink would give reason to use medicine earlier without making it life threatening. The debuff would be included in other stages as well.
Anyways they are just some ideas on how to make infection and medicine more important gameplay mechanics