The National Immunisation Advisory Committee (NIAC) advise haematopoietic stem cell transplant (HSCT) recipients should be viewed as “never immunised” and require re-immunisation post-transplant because pre-transplant ablation of haematopoietic cells in the bone marrow eliminates immune memory.
Immunity after transplant must be at least partially reconstituted for a vaccine to mount a clinically significant response. B cell counts recover by six months after autologous HSCT and by nine months after allogenic HSCT.
As people who have received a HSCT are considered “never immunised” they are the only group that require repeat of the Primary COVID-19 vaccine course. The repeat Primary COVID-19 vaccine course may be commenced six to 12 months after HSCT.
However because B-cell immune reconstitution is highly variable after HSCT in patients with primary immunodeficiencies, vaccination should be delayed until there is robust evidence of functional B-cell recovery (generally 12 months)
People who have received a HSCT are immunocompromised.
The most recent advice from the National Immunisation Advisory Committee is that anyone who is immunocompromised ( by treatment or disease) from the age of 6 months is recommended a Primary Course of two doses of Comirnaty® XBB.1.5 mRNA COVID-19 vaccine with an interval of four weeks between doses one and two.
NIAC advise that if any patient is considering severely immunocompromised their specialist may recommend a 3rd COVID -19 vaccine after an interval of 8 weeks from the 2nd COVID-19 vaccine. So a 3rd COVID-19 vaccine can only be recommended by the patient’s specialist.
If the 3rd dose of COVID-19 vaccine is considered urgent by the specialist an interval of 4 weeks can be used.
COVID-19 vaccines can be given with or at any time interval after any of the other vaccines recommended after a HSCT.
The patient is next recommended seasonal booster vaccines as per current NIAC advice.
See Chapter 3 Table 3.9 and Chapter 5a Table 5a.1 Immunisation Guidelines available at
https://www.rcpi.ie/Healthcare-Leadership/NIAC/Immunisation-Guidelines-for-Ireland
