Improved immunologic response to COVID‐19 vaccine with prolonged dosing interval in haemodialysis patients

Vaccination against 2019 coronavirus disease (COVID‐19) can reduce disease incidence and severity. Dialysis patients demonstrate a delayed immunologic response to vaccines. We determined factors affecting the immunologic response to COVID‐19 vaccines in haemodialysis patients. All patients within a Swedish haemodialysis network, vaccinated with two doses of COVID‐19 vaccine 2‐8 weeks before inclusion, were eligible for this cross‐sectional study. Severe adult respiratory syndrome coronavirus 2 (SARS‐CoV‐2) spike protein antibody levels were determined by EliA SARS‐CoV‐2‐Sp1 IgG test (Thermo Fisher Scientific, Phadia AB) and related to clinical and demographic parameters. Eighty‐nine patients were included. Patients were vaccinated with two doses of Comirnaty (BNT162b2, 73%) or Spikevax (mRNA‐1273, 23,6%). Three patients received combinations of different vaccines. Response rate (antibody titres >7 U/mL) was 89.9%, while 39.3% developed high antibody titres (>204 U/mL), 47 (43‐50) days after the second dose. A previous COVID‐19 infection associated with higher antibody titres (median (25th‐75th percentile) 1558.5 (814.5‐3,763.8) U/mL vs 87 (26‐268) U/mL, P = .002), while time between vaccine doses did not differ between groups (P = .7). Increasing SARS‐CoV‐2 antibody titres were independently associated with increasing time between vaccine doses (B 0.241, P = .02), decreasing serum calcium levels (B −0.233, P = .007) and previous COVID‐19 (B 1.078, P < .001). In conclusion, a longer interval between COVID‐19 mRNA vaccine doses, lower calcium and a previous COVID‐19 infection were independently associated with a stronger immunologic vaccination response in haemodialysis patients. While the response rate was good, only a minority developed high antibody titres, 47 (43‐50) days after the second vaccine dose.