Immune responses to a single dose of the AZD1222/Covishield vaccine in health care workers
Chandima Jeewandara, Achala Kamaladasa, Pradeep Darshana Pushpakumara, Deshni Jayathilaka, Inoka Sepali Aberathna, Danasekara Rallage Saubhagya Rasika Danasekara, Dinuka Guruge, Thushali Ranasinghe, Shashika Dayarathna, Thilagaraj Pathmanathan, Gayasha Somathilake, Panambara Arachchige Deshan Madhusanka, Shyrar Tanussiya Ramu, Tibutius T. P. Jayadas, Heshan Kuruppu, Ayesha Wijesinghe, Herath Mudiyanselage Thashmi Nimasha, Dushantha Milroy, Achini Anuja Nandasena, Poththawela Kankanam Gamage Nilanka Sanjeewani, Ruwan Wijayamuni, Sudath Samaraweera, Lisa Schimanski, Tiong Kit Tan, Tao Dong, Graham S. Ogg, Alain Townsend, Gathsaurie Neelika Malavige
Abstract
Several COVID-19 vaccines have received emergency approval. Here we assess the immunogenicity of a single dose of the AZD1222 vaccine, at one month, in a cohort of health care workers (HCWs) (629 naïve and 26 previously infected). 93.4% of naïve HCWs seroconverted, irrespective of age and gender. Haemagglutination test for antibodies to the receptor binding domain (RBD), surrogate neutralization assay (sVNT) and ex vivo IFNγ ELISpot assays were carried out in a sub-cohort. ACE2 blocking antibodies (measured by sVNT) were detected in 67/69 (97.1%) of naïve HCWs. Antibody levels to the RBD of the wild-type virus were higher than to RBD of B.1.1.7, and titres to B.1.351 were very low. Ex vivo T cell responses were observed in 30.8% to 61.7% in naïve HCWs. Previously infected HCWs, developed significantly higher (p < 0.0001) ACE2 blocking antibodies and antibodies to the RBD for the variants B.1.1.7 and B.1.351. This study shows high seroconversion after one vaccine dose, but also suggests that one vaccine dose may be insufficient to protect against emerging variants.