Immunogenicity and clinical effectiveness of mRNA vaccine booster against SARS‐CoV‐2 Omicron in patients with haematological malignancies: A national prospective cohort study

Abstract

SummaryInformation regarding the protective anti‐SARS‐CoV‐2 antibody levels and the effectiveness of the mRNA vaccines against the Omicron variant in patients with haematological malignancies is limited. We prospectively followed two times BNT162b2 vaccinated oncohaematological patients (n = 1010) without prior COVID‐19 for PCR‐confirmed breakthrough infections during the Alpha/Delta and the Omicron phases of the pandemic. Anti‐S1‐IgG levels were longitudinally monitored in patients who had received the third (booster) vaccine dose. Patients with anti‐S1‐IgG levels <50 BAU/mL 1 month after the booster had a higher risk of Omicron infections (RR 1.91; 95% CI 1.39–2.63; p = 0.0001) and severe infections (RR 8.74; 95% CI 3.99–19.1; p < 0.0001). Conversely, the risk of severe COVID‐19 was <1% with anti‐S1‐IgG levels >500 BAU/mL and neutralizing antibody concentrations >50 U/mL. The risks of breakthrough Omicron infections (HR 0.55; 95% CI 0.32–0.96; p = 0.034) and severe COVID‐19 (HR 0.27; 95% 0.11–0.7; p = 0.0074) were lower among patients who had received the booster dose. In conclusion, low antibody levels are associated with significantly increased risk of both the breakthrough Omicron infections and severe COVID‐19. The third mRNA vaccine dose improved the protection against the Omicron and reduced the risk of severe disease.