Abstract
Viral vectors have been frequently applied for vaccine development. It has also been the case for vaccines against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) to tackle the coronavirus disease 2019 (COVID-19) pandemic. A multitude of different viral vectors have been mainly targeting the SARS-CoV-2 spike (S) protein as antigen. Intramuscular injection has been most commonly used, but also intranasal administration has been tested. Adenovirus vector-based vaccines are the most advanced with several vaccines receiving Emergency Use Authorization (EUA). The simian ChAdOx1 nCoV-19 vaccine applied as a prime-boost regimen has provided 62.1–90% vaccine efficacy in clinical trials. The Ad26.COV2.S vaccine requires only one immunization to provide protection against SARS-CoV-2. The rAd26-S/rAd5-S vaccine utilizes the Ad26 serotype for the prime immunization followed by a boost with the Ad5 serotype resulting in 91.2% vaccine efficacy. All adenovirus-based vaccines are used for mass vaccinations. Moreover, vaccine candidates based on vaccinia virus and lentivirus vectors have been subjected to clinical evaluation. Among self-replicating RNA viruses, vaccine vectors based on measles virus, rhabdoviruses, and alphaviruses have been engineered and tested in clinical trials. In addition to the intramuscular route of administration vaccine candidates based on influenza viruses and adenoviruses have been subjected to intranasal delivery showing antibody responses and protection against SARS-CoV-2 challenges in animal models. The detection of novel more transmissible and pathogenic SARS-CoV-2 variants added concerns about the vaccine efficacy and needs to be monitored. Moreover, the cause of recently documented rare cases of vaccine-induced immune thrombotic thrombocytopenia (VITT) must be investigated.
Highlights
The current coronavirus disease 2019 (COVID-19) pandemic has triggered an intensive race to develop numerous vaccine candidates targeting severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) [1]
This review focuses uniquely on viral vector-based COVID-19 vaccines, describing their specific features, preclinical studies in animal models, and clinical evaluation in humans
Application of viral vectors for the development of COVID-19 has been extremely successful leading to Emergency Use Authorization (EUA) for several adenovirus-based vaccines in roughly one year since the onset of the pandemic
Summary
The current coronavirus disease 2019 (COVID-19) pandemic has triggered an intensive race to develop numerous vaccine candidates targeting severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) [1]. In addition to the intramuscular route of administration vaccine candidates based on influenza viruses and adenoviruses have been subjected to intranasal delivery showing antibody responses and protection against SARS-CoV-2 challenges in animal models. Various viral delivery vectors based on adenoviruses, vaccinia viruses, lentiviruses, measles virus, rhabdoviruses, alphaviruses and influenza viruses have been engineered for SARS-CoV-2 vaccines and subjected to preclinical studies in animal models and clinical evaluation in healthy volunteers (Table 1).
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