Omicron BA.4/5 Neutralization and T-Cell Responses in Organ Transplant Recipients After Booster Messenger RNA Vaccine: A Multicenter Cohort Study

Clin Infect Dis. 2023 Jul 26;77(2):229-236. doi: 10.1093/cid/ciad175.


Background: In solid organ transplant (SOT) recipients, the primary vaccination series against Coronavirus Disease 2019 is 3 doses followed by boosters. We determined whether a fourth dose booster induced Omicron BA.4/5 neutralizing antibodies (nAbs) and T cells in a large multicenter cohort study.

Methods: Serum was collected 4-6 weeks post-third and post-fourth doses of messenger RNA vaccine in 222 SOT recipients. nAbs were measured using a pseudovirus neutralization assay that targeted the Omicron BA.4/5 spike protein. A subset underwent T-cell testing.

Results: The median age of the cohort was 63 years (interquartile range [IQR], 50-68) with 61.7% men. BA.4/5 nAb detection increased from 26.6% (59 of 222) post-third dose to 53.6% (119 of 222) post-fourth dose (P < .0001). In patients with breakthrough infection prior to the fourth dose (n = 27), nAbs were detected in 77.8% and median nAb titers were significantly higher compared with those with 4 vaccine doses alone (P < .0001). Factors associated with a low BA.4/5 neutralization response after the fourth dose were older age (odds ratio [OR], 0.96; 95% confidence interval [CI], .94-.99), mycophenolate use (OR, 0.39; 95% CI, .20-.77) and prednisone use (OR, 0.34; 95% CI, .18-.63), and vaccine type (OR, 0.72; 95% CI, .51-.99), while breakthrough infection prior to the fourth dose (OR, 3.6; 95% CI, 1.3-9.9) was associated with a greater nAb response. Polyfunctional BA.4/5-specific CD4+ T cells significantly increased after 4 doses and were identified in 76.9% of patients at a median frequency of 213/106 cells (IQR, 98-650).

Conclusions: In summary, a booster significantly increases BA.4/5-specific neutralization and polyfunctional CD4+ T-cell responses, suggesting protection from severe disease even with new Omicron variants. However, SOT recipients who are older and on mycophenolate and prednisone need additional preventative strategies.

Keywords: SARS-CoV-2; immunity; immunocompromised; mRNA vaccine; prospective.

Publication types

  • Multicenter Study
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Antibodies, Neutralizing
  • Antibodies, Viral
  • Breakthrough Infections
  • COVID-19*
  • Cohort Studies
  • Female
  • Humans
  • Immunosuppressive Agents / therapeutic use
  • Male
  • Middle Aged
  • Organ Transplantation*
  • Prednisone
  • RNA, Messenger
  • SARS-CoV-2
  • Transplant Recipients
  • mRNA Vaccines


  • Prednisone
  • Antibodies, Neutralizing
  • Immunosuppressive Agents
  • RNA, Messenger
  • mRNA Vaccines
  • Antibodies, Viral

Supplementary concepts

  • SARS-CoV-2 variants