Dawg is right. Chickens can get many types of worms.Wazine only kills one type of worm. The only way to tell what kind of worms your chicken actually has, if any, is to take a fecal sample to a veterinarian or humane society veterinarian. You don't have to take the chicken in, just a poop sample from several chickens in your coop in a ziplock bag. Then they can tell you if your chickens have worms and what kind of worms they have. .
If a vet won't do a fecal sample for you - call another office. Lots of us check our flocks for worms on a regular basis. We only treat when we need to but we check at least yearly. This saves LOTS of EGGS! And money also!