Severe acute respiratory syndrome (SARS) coronavirus 2 (SARS-CoV-2), a novel positive-strand RNA coronavirus of Coronaviridae family, is responsible for causing devastating COVID-19 pandemic causing millions of deaths across the globe (1).SARS-CoV-2 genome contains non-structural and structural proteins including envelope (E), membrane (M), and nucleocapsid (N) and spike (S). DuringSARS-CoV-2course of infection, the S glycoproteins interacts with angiotensin converting enzyme 2 (ACE2) across the epithelial Alveolar type 2 progenitor (AT2) cells and regulate multiple intracellular biochemical mechanisms and pathways to favor viral pathogenesis (2).
To date, majority of COVID-19 vaccine strategies aim to induce neutralizing antibodies against S, therefore blocking SARS-CoV-2early-stage infection (3). According to WHO, globally 63 candidate vaccines are in human clinical trials, while more than 172 candidates are in preclinical development stages (4). Among major COVID-19 vaccines in developmental stage only Gam-COVID-Vac or Sputnik V utilized heterologous (adenovirus 5 and adenovirus 26) prime-boost recombinant adenovirus approach given 21 days apart (to overcome any pre-existing adenovirus immunity) responsibly provoked humoral and cellular immune response among 98% and 100% volunteers, respectively (5, 6).
Post-intramuscular injection of Sputnik V, the replication deficient Ad26 and Ad5 penetrate to host cells and deliver recombinant DNA into the nucleus to stimulate transcription via synthesizing mRNAs translated into spike proteins that migrate onto cell surface. The vaccinated cells may break spike proteins into fragments. Afterwards, protruding spikes or spike protein, recognized by the immune system induces strong immune responses to kill vaccinated cell. However, the cell debris containing spike proteins or fragments are taken up by antigen-presenting cell (APC), which presents fragments of the spike protein on its surface. Upon encounter with helper T cells, the B cells are activated that starts proliferation to generate antibodies against S to prevent wild type SARS-CoV-2 infection. The APC can also activate killer T lymphocytes to destroy SARS-CoV-2 infected cells displaying S protein fragments on their surfaces (7).
The Phase III clinical trial results of Gamaleya Research Institute Russia on 19,866 volunteers who received Gam-COVID-Vac or Sputnik V revealed strong efficacy, immunogenicity and safety results. The efficacy result of Sputnik V against COVID-19 was 97.6% and no serious adverse events related to the vaccine were recorded (8, 9). Among Sputnik V vaccinated volunteers, the virus neutralizing antibodies level were 1.3-1.5 times higher than level of antibodies who recovered from wild typeSARS-CoV-2 infection (6). In context of COVID-19 vaccines, it is precisely these neutralizing antibodies which are of paramount importance. Reliable quantification of the antibody responses is critical for estimating the time of protection or possible vaccine related failures.
Depending upon SARS-CoV-2 global burden of continuously increasing COVID-19, there is a dire need for mass vaccination worldwide. In resources limited low-income countries like Pakistan, healthcare system is fragile and detection of the neutralizing antibodies against SARS-CoV-2 might be crucial in formulating new vaccination strategies to curtail unprecedented COVID-19 epidemics. To date, 0.8 million people have been infected with COVID-19 in Pakistan and caused deaths in 16,999 individuals. As of 21 April 2021, 1,548,714 vaccine doses have been administered among general public (10). We aimed to evaluate SARS-CoV-2 spike antibody levels among Sputnik V vaccinated group of individuals in Pakistani population.