Prospective Assessment of Humoral and Cellular Immune Responses to a Third COVID-19 mRNA Vaccine Dose Among Immunocompromised Individuals

Background Improved coronavirus disease 2019 (COVID-19) prevention is needed for immunocompromised individuals.Methods A prospective study was performed of health care workers (HCW) and immunocompromised participants with baseline serology following 2 mRNA vaccine doses and who were retested after dose 3 (D3); multivariable regression was used to identify predictors of serological responses. IFN-gamma/TNF-alpha T-cell responses were assessed in a subset.Results In total, 536 participants were included: 492 immunocompromised (206 solid organ transplant [SOT], 128 autoimmune, 80 hematologic malignancy [HM], 48 solid tumor, 25 HIV), and 44 HCW. D3 significantly increased spike IgG levels among all, but SOT and HM participants had the lowest median antibody levels post-D3 (increase from 0.09 to 0.83 and 0.27 to 1.92, respectively), versus HCW and persons with HIV, autoimmune conditions, and solid tumors (increases from 4.44 to 19.79, 2.9 to 15.75, 3.82 to 16.32, and 4.1 to 25.54, respectively). Seropositivity post-D3 was lowest for SOT (49.0%) and HM (57.8%), versus others (>90%). Neutralization post-D3 was lowest among SOT and HM. Predictors of lower antibody levels included low baseline levels and shorter intervals between vaccines. T-cell responses against spike increased significantly among HCW and nonsignificantly among immunocompromised individuals.Conclusions D3 significantly improves serological but not T-cell responses among immunocompromised individuals. SOT and HM patients have suboptimal responses to D3.