kittens still sneezing at 5 months

Hi,  I have two kittens that I brought home in June.  They started sneezing and had antibiotic treatment.  Our boy is better but the girls is not and she had another round of the antibiotics but is still sneezing.  Our older cat  has not caught what these two seem to have.  Had to delay vaccinations initially but they both had one last week and are scheduled for another in 2 weeks.  They eat, drink, play, and sleep normally.  Vet said to let it run its course but if it continues after next shot she will start doxycyclin for the girl.  Has anyone ever experienced kittens sneezing so much and for so long and should I be worried?  Is there anything else I can do?

You may want to add lactoferrin, made from bovine colostrum.  May members have had great results with it clearing up old URI residual infections.  It stimulates the immune system.  Here is just ONE thread that has gone on awhile and discusses this.  You can search for more.

http://www.thecatsite.com/t/267703/stubborn-herpes-infection-add-lactoferrin-in-addition-to-lysine