Immune Responses Following the First Dose of the Sputnik V (Gam-COVID-Vac)

Background: As the first dose of Sputnik V Gam-COVID-Vac, is currently used as a single dose vaccine in some countries, we investigated the immunogenicity of a single dose of this vaccine in Sri Lankan adults at 4 weeks and compared the immune responses with our previously published data following AZD1222.Methods: SARS-CoV-2 antibodies were assessed at 504 individuals at the time of recruitment and at 4 weeks since receiving the single dose in Sri Lankan adults. ACE2 receptor blocking antibodies, antibodies to the receptor binding domain (RBD) of variants of concern, ex vivo IFNγ ELISpot responses, intracellular cytokine assays and B cell ELISpot assays were carried out in a sub-cohort.Findings: Of the 327/504 individuals who were baseline seronegative, 88.7% seroconverted, with significantly lower seroconversion rates in those >60-years old (p-value = 0.004) and significantly lower than previously seen with AZD1222 (p=0.018). 82.6% developed ACE2 receptor blocking antibodies, although the levels were significantly lower than seen following natural infection (p=0.0009) and following a single dose of AZD1222 (p<0.0001). Similar titres of antibodies were observed to the RBD of the WT, B.1.1.7 and B.1.617.2 compared to AZD1222, while the levels for B.1.351 were significantly higher (p=0.006) for Gam-COVID-Vac. 30% of individuals developed ex vivo IFNγ ELISpot responses, and high frequency of CD107a expressing T cells along with memory B cell responses. The ex vivo IFNγ responses for spike protein were significantly higher (p<0.0001) for AZD1222 than for Gam-COVID-Vac.Interpretation: A single dose of Sputnik V Gam-COVID-Vac induced high seroconversion rates although lower responses in older age groups in Sri Lankan adults. The overall antibody responses, ACE2 receptor blocking antibody responses and ex vivo T cell responses appear to be significantly lower than previously seen with AZD1222, and so there is likely to be benefit from delivery of the second dose.Funding: We are grateful to the World Health Organization, UK Medical Research Council. theForeign and Commonwealth Office and NIH, USA (grant number 5U01AI151788-02) for support.T.K.T. is funded by the Townsend-Jeantet Charitable Trust (charity number 1011770) and the EPACephalosporin Early Career Researcher Fund.Declaration of Interest: None of the authors have any conflicts of interest.Ethical Approval: Ethics approval was obtained from the Ethics Review Committee of University of Sri Jayewardenepura (COVID 01/21).