If your child has had the first round of the chicken pox vaccine, can he still get chicken pox before his second vaccine?

Yes.: The first vaccination is only 80-85% effective, meaning your child has a 15-20% chance of getting chicken pox after one vaccination. That's why the second shot is recommended. Even after two shots, there is still a chance that the child is still susceptible, but it's a very small chance, probably less than 1%.

Yes: The single vaccine does not give full immunity and some children will get chickenpox before receiving the 2nd vaccine. Usually it is very mild.