Hi, I had gone through your question and understand your concerns.
There are two possibilities as it is not clear by your question that after how many days of vaccinations these blisters appear.
First possibility is
vaccine associated
rash, that appear in 1-3 percent of individuals ,1-3 weeks after
chickenpox vaccine , resolves itself and does not require any specific treatment.
Second possibility is breakthrough
varicella (chickenpox) , chance of which are one in five individuals receiving one dose of chickenpox vaccine , and very much less after two doses of chickenpox vaccine. Illness is very mild, with almost no
fever, or complications as compared to disease in non-vaccinated individuals.
Hope this answers your question. If you have additional questions , do not hesitate in writing to us.
Wishing your baby good health.