What is the mechanism of Gam-COVID-Vac?

Gam-COVID-Vac, more commonly known as Sputnik V, is a vaccine developed by the Gamaleya Research Institute of Epidemiology and Microbiology in Russia to combat COVID-19. Understanding the mechanism of Gam-COVID-Vac can provide insights into its design, functionality, and the scientific principles behind its efficacy.

At its core, Gam-COVID-Vac is a viral vector vaccine that employs a novel, yet effective, approach to trigger an immune response. Specifically, it uses two different adenoviruses, Ad26 and Ad5, to deliver genetic material from the SARS-CoV-2 virus, which causes COVID-19, into human cells. Adenoviruses are common viruses that typically cause mild respiratory infections, but in the case of this vaccine, they are engineered to be replication-deficient, meaning they cannot multiply within the human body or cause disease.

The vaccine is administered in two doses, with each dose utilizing a different adenovirus vector. The first dose uses Ad26, and the second dose, given 21 days later, uses Ad5. This heterologous prime-boost strategy is designed to enhance the immune response and avoid potential issues related to pre-existing immunity against the adenovirus vectors.

Once the vaccine is injected, the adenovirus vectors, carrying the gene for the SARS-CoV-2 spike protein, enter the host's cells. The spike protein is a crucial component of the virus, allowing it to attach and enter human cells. Inside the host cells, the adenovirus vectors release the genetic instructions to produce the spike protein. The host cells then use these instructions to synthesize the spike protein and present it on their surfaces.

The presence of the spike protein on the surface of host cells triggers the immune system to recognize it as foreign. This activates both arms of the adaptive immune response: the humoral and cellular responses. The humoral response involves the production of antibodies by B cells that specifically target the spike protein. These antibodies can neutralize the virus, preventing it from infecting cells in the future. The cellular response involves the activation of T cells, which can identify and destroy infected cells displaying the spike protein.

By using two different adenovirus vectors, the vaccine minimizes the risk of the immune system developing a strong response against the vector itself after the first dose, which could reduce the effectiveness of the second dose. This approach enhances the overall immune response to the spike protein, leading to robust and long-lasting immunity.

In summary, Gam-COVID-Vac, or Sputnik V, employs a dual-vector, viral vector vaccine strategy to deliver the genetic code for the SARS-CoV-2 spike protein into human cells. By leveraging the body's own cellular machinery to produce this protein, the vaccine stimulates both antibody production and cellular immunity, providing comprehensive protection against COVID-19. The use of two different adenoviral vectors in a prime-boost regimen is a key feature that enhances the vaccine's effectiveness, ensuring a strong and durable immune response.