Yes. It often takes several cycles of worming to clear worms from a dog's gastrointestinal tract. The medications often kill the adult form of the worms and you then have to worm the dog again to kill the new adults from the larvae and eggs that may have been in the intestine when first wormed.
With fleas, if the outside environment was not treated in addition to the dog and the home inside, it is possible for the dog to keep picking up fleas.
Sabra - female GSD - born April 30, 2012
Sargeant - rescued senior GSD male/foster failure - approximately ten years old (August 2013)
Max - rescued GSD - Dec 22, 2010 to March 7, 2012 - at the bridge
Sable - rescued GSD - at the bridge