I Just Took My Twins To Get Their 2nd Vaccine

i just took my twins to get their 2nd vaccine pentacle at 6 months. the doctor just called me and said the vaccine they gave them has expired 3 months ago. I was wondering what are the side effects if any for getting an expired vaccine?
Also, the doctor hasn't ran into this problem and the other doctors she talked to are 50-50 on either letting it be because they believe it will still work or redoing the shot since it may not be effective since it expired. I was wondering what are the side effects if we decide to redo the shot for getting an extra dose of the pentacle vaccine?
Out of the two options what do you think I should do? Redo the shot or not?