What is the dose of Act-HIB (Haemophilus influenzae type b) vaccine for individuals undergoing splenectomy?

Haemophilus influenzae Type b (Hib) Vaccination for Splenectomy Patients

For individuals undergoing splenectomy, administer a single 0.5 mL intramuscular dose of any licensed Hib conjugate vaccine (Act-HIB, Hiberix, or PedvaxHIB), preferably at least 14 days before elective surgery, or at least 14 days after emergency splenectomy once the patient is stable. 1

Dosing Specifications

• Standard dose: 0.5 mL administered intramuscularly 1
• Number of doses: One single dose for unvaccinated patients aged ≥15 months 1
• Route: Intramuscular injection 1

Optimal Timing Strategy

For elective splenectomy:

• Administer at least 14 days before the surgical procedure to allow optimal antibody response 1, 2
• Some experts recommend vaccination regardless of prior vaccination history 1
• The 14-day pre-surgery window is critical because it allows adequate time for protective antibody formation before functional asplenia occurs 2, 3

For emergency splenectomy:

• Administer at least 14 days after surgery once the patient's condition is stable 2, 3, 4
• Delaying beyond 14 days provides no additional immunologic benefit 4

Age-Specific Dosing Guidelines

Children aged 12-59 months at high risk (including asplenia): 1

• If received 0-1 dose before age 12 months: Give 2 additional doses 8 weeks apart 1
• If received ≥2 doses before age 12 months: Give 1 additional dose at least 8 weeks after the last dose 1

Patients aged ≥15 months undergoing elective splenectomy: 1

• If unvaccinated: 1 dose prior to procedure 1

Asplenic patients aged ≥5 years: 1

• One dose if unvaccinated 1, 2
• No revaccination needed if childhood Hib series was completed 2

Special Populations Requiring Modified Approach

Hematopoietic stem cell transplant recipients: 1

• Require 3-dose regimen regardless of vaccination history 1
• Begin 6-12 months after successful transplant 1
• Separate doses by at least 4 weeks 1

Patients receiving chemotherapy or radiation: 1

• Avoid vaccination during active treatment due to suboptimal antibody response 1
• If vaccinated within 14 days of starting immunosuppressive therapy: Consider unimmunized and repeat doses ≥3 months after completing chemotherapy 1
• If vaccinated >14 days before chemotherapy: No revaccination needed (except HSCT recipients) 1

Product Interchangeability

• All licensed monovalent Hib conjugate vaccines are interchangeable for both primary and booster doses 1
• Act-HIB (PRP-T), Hiberix (PRP-T), and PedvaxHIB (PRP-OMP) can be used interchangeably 1
• Any licensed Hib conjugate vaccine is acceptable for the single dose in asplenic patients 1

Critical Clinical Pitfalls to Avoid

Do NOT skip Hib vaccination even if the patient received childhood immunizations—unvaccinated asplenic adults require one dose 1, 2

Do NOT vaccinate during active chemotherapy or radiation therapy—wait at least 3 months after completion 1

Do NOT forget that asplenic patients face lifelong infection risk—while Hib vaccination doesn't require boosters like pneumococcal and meningococcal vaccines, the single dose is mandatory 1, 2

Do NOT delay vaccination indefinitely if the 14-day pre-surgery window is missed—administer as soon as the patient is stable post-operatively 2, 3, 4

Supporting Evidence for This Recommendation

The recommendation for a single 0.5 mL dose is based on consistent guidance from the Advisory Committee on Immunization Practices (ACIP) 1, the Infectious Diseases Society of America 1, and multiple international guidelines 1. While the evidence quality for Hib vaccination in asplenic patients is lower than for pneumococcal vaccination (based on smaller studies and extrapolation from other high-risk groups) 1, the recommendation is strong because Haemophilus influenzae type b can cause overwhelming post-splenectomy infection with high mortality rates 2, 4.

Research demonstrates that Hib conjugate vaccines produce robust antibody responses in splenectomized patients, with all patients achieving protective antibody levels (>1 μg/mL) after vaccination 5, 6. The conjugate vaccine formulation produces significantly higher antibody concentrations than pure polysaccharide vaccines 6.