How many doses of the Haemophilus influenzae type b (Hib) vaccine are typically administered?

Haemophilus Influenzae Type b (Hib) Vaccine Dosing

The number of Hib vaccine doses depends on the vaccine type and the child's age at vaccination start: healthy infants receive either 3 or 4 total doses (2-3 primary doses plus 1 booster), while catch-up schedules vary from 1-3 doses based on age at first vaccination. 1

Routine Vaccination Schedule for Infants

For infants starting vaccination at 2 months of age:

• PRP-T vaccines (ActHib, Pentacel, MenHibRix, Hiberix): 4 total doses = 3 primary doses at 2,4, and 6 months + 1 booster at 12-15 months 1, 2

• PRP-OMP vaccines (PedvaxHIB, Comvax): 3 total doses = 2 primary doses at 2 and 4 months + 1 booster at 12-15 months 1, 2

• The first dose can be given as early as 6 weeks of age 1

• Primary series doses should be spaced 8 weeks apart (minimum 4 weeks acceptable if necessary) 1

• The booster dose must be given at least 8 weeks after the most recent vaccination 1

Catch-Up Vaccination Schedules

The number of doses required for catch-up depends critically on the child's age at first vaccination:

Starting at Age <7 Months

• 3-4 total doses: 2 doses of PRP-OMP or 3 doses of PRP-T (minimum 4 weeks apart) + 1 booster at 12-15 months 1

Starting at Age 7-11 Months

• 3 total doses: 2 doses at least 4 weeks apart + 1 final dose at 12-15 months or 8 weeks after the second dose, whichever is later 1

Starting at Age 12-14 Months

• 2 total doses: Given 8 weeks apart, no third dose needed 1

Starting at Age 15-59 Months

• 1 dose only: No further doses needed for healthy children 1, 3

High-Risk Children Requiring Additional Doses

Children with certain conditions need additional vaccination beyond routine schedules. High-risk conditions include functional or anatomic asplenia, HIV infection, immunoglobulin deficiency, early component complement deficiency, chemotherapy/radiation therapy, or hematopoietic stem cell transplant. 1

For high-risk children aged 12-59 months:

• If unvaccinated or received 0-1 dose before age 12 months: 2 doses, 8 weeks apart 1

• If received ≥2 doses before age 12 months: 1 dose, 8 weeks after last dose 1

• If completed primary series and booster at ≥12 months: No additional doses 1

For hematopoietic stem cell transplant recipients (any age):

• 3 doses regardless of prior vaccination history, beginning 6-12 months after transplant, at least 4 weeks apart 1

Critical Pitfalls to Avoid

Do not over-vaccinate healthy children: After age 15 months, healthy children without high-risk conditions need at most 1 catch-up dose if unvaccinated. 4 By age 3 years, children have developed natural immunity to Hib, making additional doses unnecessary unless high-risk conditions exist. 3

Do not under-vaccinate high-risk children: Failing to identify conditions like asplenia, HIV, or immunodeficiency leads to inadequate protection in vulnerable populations who need additional doses. 4

Vaccine type matters for primary series completion: If PRP-OMP was used for both primary doses, no third primary dose is needed. If vaccine type is uncertain or mixed, assume a 3-dose primary series is required. 1