Review of COVID-19 viral vector-based vaccines and COVID-19 variants.

The concept of viral vector-based vaccine was introduced in 1972 by Jackson et al and in 1982 Moss et al introduced the use of vaccinia virus as a transient gene expression vector. The technology has been used to make Ebola vaccines and now COVID-19 vaccines. There are two types of viral vector-based vaccines i.e. replicating and non-replicating. Non-replicating viral vector-based vaccines use replication-deficient viral vectors to deliver genetic material of a particular antigen to the host cell to induce immunity against the desired antigen. Replicating vector vaccines produce new viral particles in the cells they enter, which then go on to enter more new cells which will also make the vaccine antigen. Non-replicating vector-based vaccines are more commonly utilized. Adenovirus, vesicular stomatitis virus, vaccinia virus, adenovirus associated virus, retrovirus, lentivirus, cytomegalovirus, and sendai virus have been used as vectors. Current adenovirus vector-based vaccines being administered against SARS-CoV-2 infection are JNJ-78435735 by Johnson and Johnson (Janssen) along with Beth Israel Deaconess Medical Center, AZD1222 by Oxford-AstraZeneca, Sputnik V and Sputnik Light by Gamaleya Research Institute of Epidemiology and Microbiology, and Convidecia vaccine by CanSino Biologics. Of the five vaccines, the United States Food and Drug Administration (FDA) has approved Janssen vaccine for emergency use. Efficacy against COVID-19 variants has been found in all but the Convidecia vaccine so far. Heterologous prime-boost COVID-19 vaccination regimen may be the new face and more efficient immunization approach for enhanced immunity against COVID-19.