Vaccine
Talk

Recipients of haematopoietic stem cell transplants (HSCT) are at increased risk of vaccine-preventable diseases due to prolonged immunosuppression and the loss of pre-existing immunity. Both autologous and allogeneic HSCT recipients may lose protective immunity acquired through previous vaccination or natural infection, making revaccination an essential component of post-transplant care.

HSCT involves the administration of hematopoietic-ablative therapy followed by the infusion of stem cells obtained either from the recipient (autologous transplant) or from a donor (allogeneic transplant). Stem cells may be collected from:

• Peripheral blood
• Bone marrow
• Umbilical cord blood

Although autologous HSCT recipients generally recover immune function more rapidly than allogeneic recipients, both groups require systematic revaccination after transplantation.

Immunosuppression following HSCT results from several factors:

• Conditioning chemotherapy and/or radiotherapy administered before transplantation
• Graft-versus-host disease (GVHD) in allogeneic HSCT recipients
• Immunosuppressive therapies used to prevent or treat GVHD
• The underlying disease that necessitated transplantation

As immune reconstitution occurs, immunologic memory from previous vaccinations gradually declines. Antibody levels against vaccine-preventable diseases such as tetanus, poliovirus, measles, mumps, rubella, and infections caused by encapsulated bacteria may decrease significantly within 1–4 years after transplantation if revaccination is not performed.

Chronic GVHD is associated with persistent immune dysfunction and functional hyposplenism, resulting in increased susceptibility to infections caused by encapsulated organisms, particularly Streptococcus pneumoniae.

Patients with chronic GVHD who remain on immunosuppressive therapy may also require antibiotic prophylaxis in addition to vaccination.

Because immune recovery varies substantially between individuals, recommendations regarding live vaccines depend on the patient's degree of immune reconstitution and immunosuppressive status.

Current guidelines generally recommend the same revaccination schedule for both autologous and allogeneic HSCT recipients regardless of:

• Stem cell source
• Conditioning regimen
• Donor type

Even patients who completed routine vaccinations before transplantation should be considered for revaccination because protective immunity may be lost after HSCT.

Most inactivated vaccines are restarted approximately 6 months after transplantation, although certain vaccines may be initiated earlier in selected circumstances.

Pneumococcal Vaccines

Haemophilus influenzae Type b (Hib) Vaccine

• A three-dose Hib series is recommended beginning 6 months after transplantation.
• Doses should be separated by at least 1 month.
• This recommendation applies regardless of whether Hib vaccine was received before HSCT.

Diphtheria, Tetanus, and Pertussis Vaccines

Influenza Vaccine

• Annual influenza vaccination is recommended lifelong.
• Routine administration should begin at least 6 months after HSCT.
• Vaccination may be considered as early as 4 months after HSCT during influenza circulation.
• If influenza vaccine is administered at 4 months post-transplant, a second dose should be considered.
• Children younger than 9 years receiving influenza vaccine for the first time should receive two doses according to standard recommendations.
• Only inactivated influenza vaccines should be used.

Hepatitis B Vaccine

Revaccination against hepatitis B is recommended after HSCT. Because vaccine response may be impaired, post-vaccination serologic testing should be performed approximately 4–6 weeks after completion of the vaccine series to assess protection and determine whether additional doses are needed.

Hepatitis A Vaccine

Hepatitis A vaccine should be re-administered according to post-transplant vaccination recommendations and may be particularly important for individuals at increased risk or those planning international travel.

Inactivated Polio Vaccine (IPV)

Revaccination with IPV is recommended because immunity to poliovirus may decline following transplantation.

Meningococcal Vaccines

Human Papillomavirus (HPV) Vaccine

HPV vaccination should be administered according to age-based recommendations:

• Routine vaccination for individuals aged 9–26 years
• Adults aged 27–45 years based on shared clinical decision-making

Recombinant Zoster Vaccine (RZV)

RZV may be administered after immune recovery:

• 6–12 months after allogeneic HSCT
• 3–12 months after autologous HSCT

Ideally, vaccination should be completed approximately 2 months before discontinuation of antiviral prophylaxis when such therapy is being used.

Live vaccines should not be administered routinely during the first 24 months after HSCT.

Live vaccines may be considered only if all of the following conditions are met:

• At least 24 months have elapsed since transplantation
• No active GVHD is present
• The patient is no longer receiving immunosuppressive therapy
• Adequate immune reconstitution has occurred

Measles, Mumps, and Rubella (MMR)

MMR vaccine may be administered under the above conditions. Serologic testing is recommended approximately 4–6 weeks after the second dose because antibody levels may guide the need for additional vaccination.

Varicella Vaccine

Varicella vaccine may be considered when the same eligibility criteria for live vaccines are met. Post-vaccination varicella serology is not recommended because currently available commercial assays are insufficiently sensitive to detect vaccine-induced immunity.

The following live vaccines are generally contraindicated after HSCT:

• Bacillus Calmette–Guérin (BCG)
• Live attenuated influenza vaccine (LAIV)
• Oral typhoid vaccine
• Rotavirus vaccine

These vaccines should not be administered to HSCT recipients.

Serological Testing Recommended

Serological Testing Not Routinely Recommended

Vaccination of stem cell donors before stem cell collection has been shown to improve early antibody responses in recipients for certain vaccines, including:

• Hepatitis B
• Tetanus
• Hib
• Pneumococcal conjugate vaccines

However, practical, logistical, and ethical considerations often limit routine implementation of donor immunization strategies.

• Centers for Disease Control and Prevention. Best Practices Guidance — Vaccination of persons who have altered immunocompetence. https://www.cdc.gov/vaccines/hcp/imz-best-practices/altered-immunocompetence.html
• Australian Government Department of Health and Aged Care. Table. Recommendations for vaccination after haematopoietic stem cell transplant in children and adults. https://immunisationhandbook.health.gov.au/resources/tables/table-recommendations-for-vaccination-after-haematopoietic-stem-cell-transplant-in-children-and-adults