If the chickens are over six months old, free range, and never been wormed, they probably have worms... many illnesses are parasite related.
Wazine actually says to not use it at all on Laying chickens... but, we all use wormers off label for chickens? I believe with Wazine I have heard it is 30 days and does not kill all worms. (not sure about the withdrawal, I choose not to use Wazine myself). Might only kill round worms and chickens get several kinds of worms.
Valbazen is a better choice in my opinion. Use the search here on BYC... and know that if you want to worm effectively, it's best to use something you give individually to each chicken...
If you worm with Wazine in the water.. how much medicine / wormer did each chicken get? Was it enough? Too much?
Search here "worming with Valbazen".. and "giving oral medications"... You will need to repeat worming in 10 days.. if you have used or want to use Wazine first.. then use Valbazen for the second dose.. all of these require withholding, not eating the chickens or the eggs for at least ... until the 15th day after the second or last dosage of worming medicine... also no "hatching" of those eggs. You can search and pay special note to good info on worming posted by dawg53 -- the more recent posts, in recent years by anyone are better, we all learn as we go.
Tapeworms take extra treatments..... harder to get rid off. And, DE does not kill worms... does not treat worms or mites in chickens.. it's nice and might help prevent some, but not all.... Sevin Dust for Mites..
Good luck.