General
Timing
Medically stable preterm (PT) and low birth weight (LBW) infants should receive all routinely recommended childhood vaccines at the same chronologic age as recommended for full-term (FT) infants. Under most circumstances, gestational age at birth and birth weight should not be limiting factors when deciding whether a PT or LBW infant is to be immunized on schedule. Infants with birth weight less than 2,000 g, however, may require modification of the timing of hepatitis B immunoprophylaxis depending on maternal hepatitis B surface antigen (HbsAg) status.
Dosing
Vaccine dosages normally given to FT infants should not be reduced or divided when given to PT and LBW infants. Although studies have shown decreased immune responses to some vaccines given to very low birth weight (VLBW), extremely low birth weight (ELBW), and very early gestational age (<29 weeks) neonates, most PT infants produce sufficient vaccine-induced immunity to prevent disease when full doses are given. The severity of vaccine-preventable diseases in PT and LBW infants precludes any delay in initiating the administration of these vaccines.
Vaccine Administration
The anterolateral thigh is the site of choice when administering intramuscular vaccines to PT infants. The choice of needle length used for intramuscular vaccine administration is made on the basis of the available muscle mass of the PT infant and may be less than the standard 7/8-inch to 1-inch length used for FT infants (Atkinson et al., 2002).
Hepatitis B
Infants Born to HBsAg-Negative Mothers
Medically stable PT infants and infants weighing greater than 2,000 g at birth should be treated like FT infants and preferentially receive the first dose of monovalent hepatitis B vaccine shortly after birth and no later than hospital discharge. Practitioners who are certain of the mother's negative HBsAg status and wish to use a hepatitis B-containing combination vaccine for PT and LBW infants with birth weight greater than 2,000 g must delay the first dose of the combination vaccine until the infant is at least 6 weeks of age. There is no contraindication to giving a birth dose of hepatitis B vaccine as the first of 4 doses when a combination vaccine containing hepatitis B vaccine subsequently is used. The final dose of hepatitis B vaccine should not be given earlier than 6 months chronologic age.
Medically stable PT and LBW infants with birth weight less than 2,000 g should receive the first dose of hepatitis B vaccine as early as 30 days of chronologic age regardless of gestational age or birth weight. Alternatively, PT and LBW infants weighing less than 2,000 g showing consistent weight gain leading to discharge home from the hospital before attaining 30 days of age should receive the first dose of hepatitis B vaccine at the time of hospital discharge.
Infants Born to HBsAg-Positive Mothers
PT and LBW infants born to mothers who are HBsAg positive must receive hepatitis B vaccine and hepatitis B immune globulin (HBIG) within 12 hours after birth, regardless of gestational age or birth weight. Infants weighing less than 2,000 g and born to HBsAg-positive mothers should not have the birth dose of hepatitis B vaccine counted as part of the hepatitis B virus (HBV) immunization series, and 3 additional doses of hepatitis B vaccine should be given starting at 1 month of age. Combination vaccines containing a hepatitis B component have not been assessed for efficacy when given to infants born to HBsAg-positive mothers. All infants of HBsAg-positive mothers should be tested for the presence of antibody to hepatitis B surface antigen (anti-HBs) and HBsAg at 9 to 15 months of age, after completion of the HBV immunization series. Some experts prefer to perform serologic testing 1 to 3 months after completion of the primary series.
Infants Born to Mothers Whose HBsAg Status Is Unknown
All PT and LBW infants born to mothers whose HBsAg status is unknown at the time of delivery should receive monovalent hepatitis B vaccine within 12 hours of birth. Because infants weighing less than 2,000 g have less predictable responses to hepatitis B vaccine given at birth, they should be given hepatitis B immune globulin by 12 hours of life if the mother's HBsAg status cannot be determined within that time period. Hepatitis B immune globulin may be delayed up to 7 days for PT and LBW infants weighing more than 2,000 g at birth while awaiting the mother's HBsAg test results.
Table 1 in the original guideline provides a schematic outline for hepatitis B immunoprophylaxis given to PT and LBW infants.
Diphtheria and Tetanus Toxoid and Acellular Pertussis (DTaP), Haemophilus influenzae Type b (Hib), and Inactivated Poliovirus (IPV) Vaccines
All medically stable PT and LBW infants should begin routine childhood immunization with full doses of any DTaP, Hib, and IPV vaccines licensed by the Food and Drug Administration at 2 months of chronologic age regardless of gestational age or birth weight. Although apnea has not been reported in ELBW infants born at less than 31 weeks' gestation after the use of DTaP vaccine alone, in conjunction with other routinely recommended childhood vaccines, or in combination with other vaccine antigens, it is deemed prudent to closely observe hospitalized ELBW infants for significant adverse events for up to 72 hours after immunization until such a time that sufficient data have been collected to firmly establish a pattern of safety.
Pneumococcal Conjugate Vaccine (PCV7)
All PT and LBW infants are considered at increased risk of invasive pneumococcal disease, and medically stable PT patients should receive full doses of PCV7 beginning at 2 months of chronologic age.
Influenza
All PT infants are considered at high risk of complications of influenza virus infection and should be offered influenza vaccine beginning at 6 months of age and as soon as possible before the beginning and during influenza season. PT and LBW infants receiving influenza vaccine for the first time will require 2 doses of vaccine administered 1 month apart.
