2367. Six-month Humoral Response Following Two Or Three Doses Of Covid-19 Vaccines As Primary Vaccination Followed Or Not By a Booster Dose In Specific Populations – ANRS0001S COV-POPART Cohort Study

BACKGROUND: The duration of humoral response in immunocompromised populations according to the number of doses in the primary vaccine regimen and the number of booster doses is little known. METHODS: Participants from the French national multi-center prospective cohort study ANRS0001S COV-POPART were included (11 specific subpopulations and 2 control groups (18-64 years and over 65 years)). We evaluated the immune response to COVID-19 vaccines up to 6 months after the second dose, distinguishing participants having received two or three doses in their initial vaccination scheme and those with or without a booster dose before 6 months. Participants with positive anti-nucleocapsid (NP) antibodies or SARS-CoV-2 infection during follow-up were excluded. Serological (ELISA EuroImmun®) and seroneutralisation (in vitro neutralization assay, original strain) tests were carried out centrally. RESULTS: 3724 participants were included: 2756 from specific subpopulations and 968 controls. Participants in specific sub-populations and the control groups mostly received two doses of BNT162b2 (68.6% and 83.6%, respectively). Fifteen percent of participants in a specific sub-population received 3 doses within their initial vaccine scheme (mostly solid organ transplants (SOT) and Hematopoietic stem cell transplants (HCT)) and 11.2% received a booster dose within 6 months after a median time of 5 months after the last dose. The control groups and all specific sub-populations who received two doses as the primary regimen, except solid SOT and HCT groups, increased their anti-Spike and seroneutralisation titer after a booster dose (Figure 1A and 1C). The booster dose had little effect on participants who received three doses as a primary vaccination regimen compared to those who did not receive the booster dose (Figure 1B and 1D). 6-month median (IQR) anti-Spike IgG titers (BAU/mL) in specific subpopulations who received two (A) and three doses (B) within their initial vaccine scheme. 6-month seroneutralisation titers in specific subpopulations who received two (C) and three doses (D) within their initial vaccine scheme. [Figure: see text] Solid organ transplantation (SOT), hematopoietic stem cell transplantation (HCT), chronic renal failure (CKD), systemic autoimmune diseases (SAD), inflammatory rheumatic diseases (IRD), multiple sclerosis (MS) or neuromyelitis optica spectrum disorders (NMOSD). CONCLUSION: A booster dose in those who received 2 doses as a primary vaccination regimen increased 6-month humoral responses in almost all sub-populations except SOT and HSCT. The effect of booster doses in those receiving three doses as a primary vaccination regimen was low, reflecting the profound immunosuppression of these patients. DISCLOSURES: Paul LOUBET, MD, PhD, Astrazeneca: Advisor/Consultant|Astrazeneca: Board Member|Moderna: Board Member|Pfizer: Advisor/Consultant|Pfizer: Board Member Odile Launay, MD, PhD, Moderna: Advisor/Consultant|Pfizer: Advisor/Consultant|Pfizer: Board Member