Neutralising antibodies among doctors and nurses at six weeks and six months following two doses of ChAdOx1 nCoV-19 corona virus vaccine at two teaching hospitals

Introduction: The presence of neutralising antibodies (NAbs) indicates protection against SARS- CoV-2 infection. Sri Lankan healthcare workers (HCWs) were vaccinated with two doses of ChAdOx1 nCoV-19 corona virus vaccine three months apart as the primary course. This study was done to determine and compare the prevalence of NAbs against SARS- CoV-2 among doctors and nurses vaccinated with a primary course of ChAdOx1 nCoV-19 corona virus vaccine at 6 weeks and 6 months and to determine the co-morbidities associated with non-development of NAbs.
Methods: A prospective descriptive study was carried out at two teaching hospitals to determine the presence of NAbs in serum of doctors and nurses who were vaccinated with 2 doses of ChAdOx1 nCoV-19 Corona virus vaccine at 6 weeks and 6 months following the 2nd dose. A total of 205 serum samples were tested for presence of NAbs by an ELISA test (C Pass ™ SARS CoV -2 Neutralization Antibody Detection Kit).
Results: At 6 weeks, 115 of 128 (89.8%) had NAbs while 58 of 77 (75.3%) had antibodies after 6 months. In the comparison group which was tested at both time points (n=55), 41 of 55 (74.5%) demonstrated persistence of NAbs while 12 of 55 (21.8%) became seronegative by 6 months. Two HCWs (3.6%) did not have antibodies at 6 weeks or at 6 months. None of the comorbidities were significantly associated with non-seroconversion at 6 weeks or sero-reversion of neutralising antibodies at 6 months.
Conclusions: The majority of HCWs developed NAbs after 6 weeks and 21% became seronegative by 6 months.