This is a summary, written by members of the CITF Secretariat, of:

Mittal A, Solera JT, Ferreira VH, Kothari S, Kimura M, Pasic I, Mattsson JI, Humar A, Kulasingam V, Ierullo M, Kumar D, Hosseini-Moghaddam SM. Immunogenicity and Safety of Booster SARS-CoV-2 mRNA Vaccine Dose in Allogeneic Hematopoietic Stem Cell Transplant Recipients. Transplant Cell Ther. 2023 Aug 13:S2666-6367(23)01465-3. doi: 10.1016/j.jtct.2023.08.008.

The results and/or conclusions contained in the research do not necessarily reflect the views of all CITF members.

A CITF-funded study, published in Transplantation and Cellular Therapy, found that a fourth dose of the COVID-19 vaccine is highly immunogenic (induces a good immune response) and safe in people who have a received an allogeneic Hematopoietic Stem Cell Transplant (HSCT). The study was led by Dr. Deepali Kumar in collaboration with Dr. Seyed M Hosseini-Moghaddam (both from University of Toronto.)

Key findings:

  • 67 patients who had received an allogenic Hematopoietic Stem Cell Transplant (HSCT) got their fourth dose of vaccine. Of those, 54 patients (61% male) with a median age of 59.5 years were included in the anti-RBD antibody titer analysis.
  • Four to six weeks after allogeneic HSCT patients had received their fourth vaccine dose, anti-RBD antibody titers had increased to 44,500 U/ml compared to 13,350 U/ml four to six weeks after the third dose.
  • A mild breakthrough SARS-CoV-2 infection occurred in six (11%) patients after the fourth dose. The median time between vaccination and infection was 91.5 days. There was no significant difference in the median anti-RBD antibody titers between the participants who developed a breakthrough SARS-CoV-2 infection and those who did not.
  • Adverse events were mild after the fourth dose and mostly included site tenderness (44%), fatigue (16%), myalgia (4%), and headache (2%). No new graft-versus-host disease (GvHD) or worsening of pre-existing GvHD was observed within 40 days of vaccination and no patient died.
  • In the multivariate analysis, only post-third dose anti-RBD antibody titers significantly predicted the antibody titers after the fourth dose.

The study findings support current recommendations and show the immunogenic benefits of booster vaccine doses in immunocompromised individuals, who are at higher risk of severe disease from SARS-CoV-2 infection than the general population.  Allogeneic HSCT patients aged ≥18, who received the fourth dose of a COVID-19 mRNA vaccine between December 15, 2021 and August 2, 2022, were included in the study. Patients with a history of COVID-19 diagnosis and those who received IVIG within 21 days of antibody testing or rituximab within six months before cohort entry were excluded from the study.