Preterm infants generally can be vaccinated at the same chronologic age as full-term infants according to the recommended childhood immunization schedule. An exception is the bih dose of hepatitis B vaccine. Infants weighing >=2 kg and who are stable may receive a bih dose. However, hepatitis B vaccination should be deferred in infants weighing <2 kg at bih until 30 days of age, if born to an HBsAg negative mother. All preterm, low bihweight infants born to HBsAg positive mothers should receive hepatitis B immunoglobulin and hepatitis B vaccine within 12 hr of bih. However, such infants should receive an additional 3 doses of vaccine staing at 30 days of ageReference: Nelson Textbook of Paediatrics; 20th edition; Chapter 172; Immunization Practices