Clin Microbiol Infect. 2022 Feb 17:S1198-743X(22)00058-1. doi: 10.1016/j.cmi.2022.02.002. Online ahead of print.
OBJECTIVE: The recent surge in COVID-19 cases led to consideration of a booster vaccine in previously vaccinated immunosuppressed individuals. However, the immunogenic effect of a third-dose SARS-CoV-2 vaccine in immunosuppressed patients is still unknown.
METHODS: This was an observational cohort study of 279 previously-vaccinated immunosuppressed patients followed at a single tertiary hospital in Israel. Patients were administered a third dose of the Pfizer-BioNTech mRNA vaccine (BNT162b2), between July 14th and July 21st, 2021. Levels of IgG antibodies against the spike receptor-binding domain of SARS-CoV-2 were measured 3-4 weeks after vaccination.
RESULTS: Of the cohort of 279 patients, 124 (44.4%) had haematologic malignancies, 57 (20.4%) had rheumatologic diseases, and 98 (35.1%) were solid organ-transplant recipients. Anti-SARS-CoV-2 antibody levels increased in 74.9% of cases. Across the entire cohort, the median absolute antibody levels (expressed in AU/mL) increased from 7 (IQR, 0.1-69) to 243 (IQR, 2-4749) after the booster dose. The response significantly varied across subgroups: the transplant cohort showed the greatest increase in absolute antibody levels (from 52 [IQR, 7.25-184.5] to 1824 [IQR 161-9686]), followed by the rheumatologic cohort (from 22 [IQR, 1-106] to 1291 [IQR, 6-6231]), and the haemato-oncological cohort (from 1 [IQR, 0.1-7] to 7.5 [IQR, 0.1-407.5]); χ2=8.30 for difference in fold-change (P=0.016). Out of 193 patients who were seronegative at baseline, 76 became seropositive after vaccination, corresponding to a 39.4% (95% CI, 32.8%-46.4%) seroconversion rate. Transplant patients had the highest seroconversion rate (58.3% [95% CI, 44.3%-71.2%]), followed by rheumatologic patients (44.1% [95% CI, 28.9%-60.5%]), and haemato-oncology patients (29.7% [95% CI, 22%-38.8%]; χ2=11.87; P=0.003).
CONCLUSIONS: A third dose of BNT162b2 is immunogenic in most immunosuppressed individuals, although antibody response may differ based on the type of disease and immunosuppression. The antibody level that correlates with protection is still unknown, thus future studies are needed to evaluate clinical outcomes.