MO842: Maintenance of Humoral Response During a Three-Dose Immunization Program With MRNA SARS-COV-2 Vaccines in the Haemodialysis Population

Abstract

BACKGROUND AND AIMS The COVID-19 pandemic continues to be a worldwide health issue. Among haemodialysis (HD) patients, many countries opted for a three-dose immunization scheme with mRNA vaccines, as some patients did not produce a sufficient humoral response after the second one, and most developed a rapid decline in antibody levels over the months following vaccination. METHOD This observational, prospective, multi-centre study evaluated the humoral response, clinical outcomes (breakthrough infections, hospital admissions, severe COVID-19 and mortality), and their potential associated factors by determining the presence and levels of IgG antibodies to the receptor-binding domain of the S1 spike antigen of SARS-CoV-2 (anti-S1-RBD IgG) before and after each of the three doses of SARS-CoV-2 mRNA vaccines with either the mRNA-1273 (Moderna) or BNT162b2 (Pfizer) in 153 patients from three dialysis units affiliated to Hospital Clínic of Barcelona (Spain). RESULTS Unlike the general population, where most individuals seroconverted after one dose, HD patients required two doses to produce a positive anti-S1-RBD IgG response in most of them. Moreover, their antibody levels waned significantly three and 6 months after vaccination (see Figure 1). The decline in antibody levels was accompanied by seroreversion in 32% of patients. Notably, despite the precipitous drop, there was a low incidence of breakthrough infections (5.9%), with only one case of severe COVID-19 that required ICU admission and no deaths up until receiving the third vaccine dose. The administration of the third dose achieved seroconversion in 3 out of 4 non- or weak responders to two doses. Active cancer and immunosuppressive treatment were related to a worse humoral response. CONCLUSION Every haemodialysis patient should receive a third-dose vaccination scheme, with a booster dose three or 6 months after receiving the second one. Despite the lack of data, immunosuppressed and active cancer patients may benefit from more frequent vaccine boosters. Further monitoring of antibody levels will be needed to assess the maintenance of the humoral response in these patients.