• Muhammad Shahid Nadeem, Akbar Ali, Maryam A Al-Ghamdi, Markus Depfenhart, Jalaluddin Azam Khan, Mazin A Zamzami, Bibi Nazia Murtaza, Imran Kazmi, and Mujadid Ur Rehman.
• Altern Ther Health Med. 2020 Aug 1; 26 (S2): 72-78.

ContextRNA viruses exhibit an extraordinary ability to evolve in a changing environment and to switch from animal hosts to humans. The ongoing COVID-19 pandemic, recognized as a respiratory disease, is an example of zoonotic transmission of the RNA virus known as SARS-CoV-2. The development and regulatory approval of a vaccine against SARS-CoV-2 pose multiple preventive and therapeutic challenges, especially during an ongoing pandemic.ObjectiveThe review intended to examine the challenges and recent achievements in the development of vaccine candidates against COVID-19.DesignThe research team performed a literature review, searching relevant and up to date information from the literature. The sources of data included Google Scholar, PubMed, NCBI, and Yahoo. The search terms used were COVID-19 challenges, SARS-CoV-2 prospective challenges, RNA viruses adoptability, host switching by RNA viruses, COVID-19 vaccines.SettingThe study took place at the digital libraries of contributing institutions. The data was combined, selected for further analysis and manuscript preparation at King Abdulaziz University.ResultsRNA viruses with high rate of genome alterations and evolution have better chances to survive in the adverse environmental conditions by adopting the alternate host species. The recent epidemics such as SARS, MERS, and COVID-19 are examples of zoonotic transmission of RNA viruses from animal species to the humans. However, the mechanisms involved in the switching-on to new host species need further investigations to control the zoonotic transmissions in near future. As of April 2020, 115 candidate vaccines were being evaluated; 78 of them had been found to be active, and a few of them are in Phase I trials. In the development of different types of vaccine candidates against COVID-19, multiple international pharmaceutical and biotechnology companies are involved.ConclusionsEmerging and re-emerging pathogenic RNA viruses pose a serious threat to human health. Little is known about the human-host adoptive mechanism for zoonotic transmission. Deep insights into the molecular mechanism responsible for the switching of animal or bird viruses to humans could provide target molecules or events to prevent such transmissions in the near future. Fast development and approval of efficacious and safe vaccines is key to the effort to provide preventive measures against COVID-19 and future viruses. However, the development and availability of a vaccine candidate is a time-consuming process and often can't be completed during an epidemic. Currently, several types of vaccines are under development, and most of them won't realistically be available in time for the present COVID-19 pandemic.

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