Preterm infants should be vaccinated at the same chronological age and according to the same schedule as full-term infants, regardless of birth weight, with the exception of the birth dose of hepatitis B vaccine. Infants weighing less than 2 kg (4.4 lb) whose mothers’ HBsAg status is either positive or unknown should receive HBIG (hepatitis B immune globulin) and hepatitis B vaccine within 12 hours of birth. This dose of hepatitis B vaccine should not be counted as a valid first dose in the series, and it should be repeated at age 1 month. If the preterm infant’s mother’s HBsAg status is negative, the infant’s first dose of hepatitis B vaccine should be withheld until the infant is chronologically 1 month of age or is ready to be discharged from the hospital, whichever occurs first. For more information, see the Vaccination of Preterm Infants section of the ACIP “General Best Practice Guidelines for Immunization”, available at www.cdc.gov/vaccines/hcp/acip-recs/general-recs/special-situations.html.