Durability of ChAdOx1 nCoV-19 (Covishield ® ) Vaccine Induced Antibody Response in Health Care Workers.

(i) Background: ChAdOx1 nCoV-19 (Covishield ® ) vaccine is widely used in India. We studied the Covishield ® induced antibody response and its durability among health care workers (HCWs) (ii) Method: HCWs received two doses (0.5 mL) four weeks apart. Blood specimens, collected before each dose, day (D)60, D150 and D270 after second dose, were tested for anti-spike antibody (ASAb) titre and neutralising antibody (%) (NAb) using Elecsys Anti-SARS-CoV-2 S (Roche) and SARS-CoV-2 NAb ELISA Kit (Invitrogen), respectively. Data are expressed as proportions and median (interquartile range) and compared using non-parametric (iii) Result: Among 135 HCWs (83 males; age 45 (37-53); 36 had pre-existing ASAb), 29 (21.5%) acquired COVID-19 after 60 (39-68) days of vaccination. ASAb titre before second dose and at D60, D150, D270 were 77.2 (19.4-329.4), 512 (114.5-9212), 149 (51.6-2283) and 2079 (433.9-8644) U/mL, respectively. Compared to those without pre-existing ASAb, titres were significantly higher before second dose (5929 vs. 41, p < 0.001), D60 (3395 vs. 234, p = 0.007) and D150 (1805 vs. 103, p < 0.001) in participants with pre-existing ASAb; NAb were also higher (80 vs. 18, p < 0.001) before second dose. Between those who acquired infection or not after vaccination, ASAb titres were comparable before second dose (77 vs. 78, p = 0.362) but significantly higher at D60 (14,019 vs. 317, p < 0.001) and D150 (2062 vs. 121, p = 0.002) in the former group, though NAb percentage were higher at D60 (87 vs. 27, p < 0.001) and D150 (79 vs. 25, p = 0.007) only (iv) Conclusions: Covishield ® induces a higher antibody titre in those with pre-existing ASAb. The vaccine induced antibody starts falling 5 months after vaccination.