A viral vector is a harmless virus that can deliver a gene to our cells that they turn into a protein. Scientists have studied the use of viral vectors for gene therapy and vaccines.
When a viral vector vaccine delivers the genetic code for our cells to make a pathogen’s protein, our immune system reacts to the presence of the protein and the viral vector. This elicits an immune response that can lead to lasting immunity.
The Sputnik V COVID-19 vaccine uses two different adenoviruses as the viral vectors. Adenoviruses are a large family of viruses that can cause the common cold.
In order to train the immune system to recognize the SARS-CoV-2 virus, which causes COVID-19, people receive the vaccine in two doses at an interval of 21 days. The first shot contains adenovirus 26 (Ad26) as the viral vector, while the second shot contains adenovirus 5 (Ad5). Both shots also contain the gene for the SARS-CoV-2 spike protein.
Scientists have chemically modified the adenoviruses in the Sputnik V COVID-19 vaccine to stop them from replicating. This means that the viral vectors cannot cause an adenovirus infection.
The vaccine also cannot cause COVID-19 because it does not contain the entire SARS-CoV-2 virus.
Our immune system reacts to the vaccine by developing antibodies specific to the SARS-CoV-2 virus and by eliciting T-cell responses. In the event of future infection, our bodies can rapidly produce these antibodies to bind to the virus and prevent it from entering our cells.
T-cells can kill infected cells. Both the viral vector and the SARS-CoV-2 spike protein play a role in building up immunity in this way.