Humoral and cellular response to the third COVID-19 vaccination in patients with inborn errors of immunity or mannose-binding lectin deficiency : A prospective controlled open-label trial.

Impaired immune response to COVID-19 (coronavirus disease 2019) vaccination has been reported in patients with inborn errors of immunity (IEI). Repetitive vaccinations are recommended for this vulnerable group. Due to the high diversity within IEI patients, additional safety and immunogenicity data are needed to better understand these aspects especially in less common immunodeficiency syndromes. In this prospective open-label clinical trial, we assessed the humoral immune response and the T‑cell response in patients with IEI or severe MBL (mannose-binding lectin) deficiency (IEI/MBLdef) after three vaccinations. A total of 16 patients and 16 matched healthy controls (HC) with suboptimal humoral response defined by anti-SARS-CoV‑2 RBD (severe acute respiratory syndrome coronavirus type 2 receptor binding domain) antibodies below 1500 BAU/ml (binding antibody units per ml) after the second COVID-19 vaccination were enrolled in this study and qualified for a third mRNA vaccine dose. After 4 weeks following vaccination, 100% of HC and 75% of IEI/MBLdef patients exhibited anti-SARS-CoV‑2 RBD antibodies > 1500 BAU/ml, although the difference was not statistically significant (75% vs. 100%; p = 0.109). Although post-vaccination IEI/MBLdef patients demonstrated significantly increased anti-SARS-CoV‑2 RBD antibodies and neutralizing antibodies compared to baseline, these responses were significantly lower in IEI/MBLdef patients compared to HCs. Notably, the third vaccination augmented the cellular immune response to both wild-type and omicron peptide stimulation. No serious adverse events were reported within the 4‑week follow-up period and, importantly, vaccination had little to no effect on the long-term disease activity and fatigue. This trial strongly supports the recommendation of repeated COVID-19 vaccinations for patients suffering from immunodeficiencies, especially when they exhibit an initially limited response to the vaccine.