Abstract
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 (pInterpretation: 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).
Highlights
The COVID-19 pandemic continues to cause devastation throughout the world, with the mortality rates being highest in countries in the African, Asian and Latin American regions with poor vaccine coverage[1]
We have investigated the immune responses of the first dose of the Gam-COVID-Vac, which is known as Sputnik light, in a Sri Lankan population, 4 weeks after receiving the first dose and compared the immune responses with our previously published data following AZD1222, which is another adenovirus vector vaccine
In the phase 1/2 studies, it was shown that the vaccine only induced neutralizing antibodies (Nabs) in 61.1% of individuals at 28 days the antibody titres were comparable to those following natural infection[6]
Summary
The COVID-19 pandemic continues to cause devastation throughout the world, with the mortality rates being highest in countries in the African, Asian and Latin American regions with poor vaccine coverage[1]. Gam-COVID-Vac (Spuntik V) is a two dose COVID-19 vaccine, which comprises two replicant-deficient recombinant adenovirus vectors[6]. The use of two types of adenovirus vectors given 21 days apart, as prime and boost, was to overcome any pre-existing immunity to adenoviruses within a given population, while enhancing the immunogenicity of the vaccine[7]. Recently the first dose of Gam-COVID-Vac (rAd26-S) was marketed by the authorities as a single-dose COVID-19 vaccine, which was claimed to have an efficacy of 78.6–83.7% among elderly individuals in Russia[10]. There are no published data regarding the real-world immunogenicity of the first dose of Gam-COVID-Vac, nor any data on antibody responses to SARS-CoV-2 variants of concern (VOCs). Based on the seroprevalence rates of adenovirus 26 in a given population, the immunogenicity of a single dose vaccine using a human adenovirus vector may change
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