Q. What should be the minimum interval between 2 doses of a vaccine?
A. Minimal interval of vaccine doses is generally 1 month for the initial doses of killed vaccines; longer intervals are needed for booster doses to provide optimal boosting. The minimal spacing for MMR vaccines is 28 days.

Q. Can all vaccines be given simultaneously?
A. All childhood vaccines can be administered simultaneously. This practice is based on extrapolation of data from multiple studies showing that most vaccines can be administered at the same time without compromising safety or immunogenicity. Thus, DTaP, Hib, IPV, hepatitis B, pneumococcal conjugate vaccine, MMR, varicella, and rotavirus vaccines can be administered simultaneously. Live virus vaccines should be given either simultaneously orat least 1 month apart.

Q. Can vaccines be mixed in the same syringe?
A. Vaccines should not be mixed in the same syringe unless specifically licensed for such use.

Q. Can vaccines of different brands be interchanged?
A. Available data support interchangeability of most vaccines produced by different manufacturers to prevent the same disease (tetanus, diphtheria, hepatitis B, and hepatitis A). However, when feasible, the same vaccine should be used for the primary series.

Q. How should vaccination be given in preterm babies?
A. Since vaccines given at birth are BCG, OPV and Hepatitis B. Studies show that response to hepatitis B vaccine may be diminished in infants with birthweight less than 2000 grams after administration of hepatitis B vaccine at birth. However, by 1 month of chronologic age, all preterm infants, regardless of initial birthweight or gestational age, are as likely to respond as adequately as do older and larger infants. Thus BCG, OPV and Hepatitis B should be given in preterm infants weighing < 2000 grams and born to HBsAg-negative mothers at 1 month of postnatal age if medically stable or at hospital discharge.