What is the recommended vaccination schedule for a child under 2 years old with the HiB (Haemophilus influenzae type b) combination vaccine?

HiB Combination Vaccine Schedule for Children Under 2 Years

All infants should begin routine Hib vaccination at 2 months of age, with the schedule depending on vaccine type: a 2-dose primary series (at 2 and 4 months) for PRP-OMP vaccines (PedvaxHIB or Comvax), or a 3-dose primary series (at 2,4, and 6 months) for PRP-T vaccines (ActHib, Pentacel, MenHibRix, or Hiberix), followed by a mandatory booster dose at 12-15 months regardless of which vaccine was used. 1, 2

Primary Vaccination Series by Vaccine Type

PRP-OMP Vaccines (2-Dose Series)

• PedvaxHIB or Comvax require only 2 doses administered at 2 and 4 months of age 1, 2
• Doses should be spaced 8 weeks apart, though a minimum interval of 4 weeks is acceptable if necessary 1, 2
• No third primary dose is needed if both doses in the primary series were PRP-OMP 1, 2
• The first dose can be given as early as 6 weeks of age 1

PRP-T Vaccines (3-Dose Series)

• ActHib, Pentacel, MenHibRix, and Hiberix require 3 doses administered at 2,4, and 6 months of age 2, 3
• Doses should be spaced 8 weeks apart, with a minimum acceptable interval of 4 weeks 1, 2
• The first dose can be administered as early as 6 weeks of age 1, 3

Critical Caveat for Mixed Vaccine Types

• If uncertainty exists about which products were used previously, or if PRP-OMP was not used for both primary doses, assume a 3-dose primary series is needed to ensure adequate protection 1, 2

Booster Dose Requirements

Every child requires a booster dose at 12-15 months, regardless of the vaccine type used in the primary series. 1, 2

• The booster must be administered at least 8 weeks after the most recent Hib vaccination 1, 2
• Any licensed Hib conjugate vaccine (monovalent or combination) can be used for the booster, regardless of primary series vaccine 1, 2
• Hiberix has a specific restriction: it should only be used for booster doses (not primary series) in children 12 months through 4 years who have received at least 1 prior Hib dose 1, 2, 3

Catch-Up Vaccination Schedules

Starting at 7-11 Months

• Administer 2 doses at least 4 weeks apart, regardless of vaccine type used 1, 2
• Give a third (final) dose at 12-15 months or 8 weeks after the second dose, whichever is later 1, 2

Starting at 12-14 Months

• Administer only 2 doses total, spaced 8 weeks apart 1, 2
• No third dose is necessary 1, 2

Starting at 15-59 Months

• Only 1 dose is needed for healthy children 1, 2, 4
• No further doses are indicated for immunocompetent children in this age group 1, 4

High-Risk Children Requiring Additional Doses

Children aged 12-59 months with the following conditions need additional vaccination beyond routine schedules: functional or anatomic asplenia (including sickle cell disease), HIV infection, immunoglobulin deficiency (including IgG2 subclass deficiency), early component complement deficiency, or those undergoing chemotherapy or radiation therapy. 1, 2, 4

Dosing for High-Risk Children (12-59 Months)

• If received 0 or 1 dose before age 12 months: Give 2 doses, 8 weeks apart 1, 2, 4
• If received ≥2 doses before age 12 months: Give 1 dose, 8 weeks after the last dose 1, 2, 4
• If completed primary series and booster at ≥12 months: No additional doses needed 1, 2, 4

Special Populations

• Hematopoietic stem cell transplant recipients require 3 doses regardless of prior vaccination history, beginning 6-12 months after successful transplant, with at least 4 weeks between doses 2, 4
• Prior to elective splenectomy, give 1 dose if unimmunized, ideally at least 14 days before the procedure 2, 4

Combination Vaccine Options

Comvax (Hib + Hepatitis B)

• Licensed for use in infants and combines PRP-OMP Hib vaccine with hepatitis B vaccine 1, 5, 6
• Follows the 2-dose primary series schedule (2 and 4 months) plus booster at 12-15 months 1
• Infants receiving a birth dose of monovalent hepatitis B will receive a total of 4 doses of hepatitis B when Comvax is used, which has not led to increased adverse reactions 6

Pentacel (DTaP-IPV-Hib)

• Contains PRP-T Hib vaccine combined with DTaP and IPV 1
• Follows the 3-dose primary series schedule (2,4, and 6 months) plus booster at 12-15 months 1, 7

MenHibRix (Hib + Meningococcal CY)

• Contains PRP-T Hib vaccine combined with meningococcal serogroups C and Y 1
• Can be used for both primary series and booster doses 1

Common Pitfalls to Avoid

• Do not assume all Hib vaccines require 3 doses: PRP-OMP vaccines only need 2 primary doses, and giving an unnecessary third dose wastes resources 1, 2
• Do not skip the booster dose: Even children who completed their primary series require the 12-15 month booster for long-term protection 1, 2
• Do not use Hiberix for primary series: This vaccine is only approved for booster doses in children who have received at least 1 prior Hib dose 1, 2, 3
• Do not forget high-risk children: Immunocompromised children may need additional doses beyond the routine schedule 1, 2, 4