The SARS-CoV-2 Vaccine Pipeline: an Overview

Abstract

Purpose of Review: The goal of this review is to provide a timely overview on efforts to develop a vaccine for the 2019 novel coronavirus SARS-CoV-2, the causative agent of coronavirus disease (COVID-19). Recent Findings: Previous research efforts to develop a severe acute respiratory syndrome coronavirus (SARS-CoV) vaccine in the years following the 2003 pandemic have opened the door for investigators to design vaccine concepts and approaches for the COVID-19 epidemic in China. Both SARS-CoV and SARS-CoV-2 exhibit a high degree of genetic similarity and bind to the same host cell ACE2 receptor. Based on previous experience with SARS-CoV vaccines, it is expected that all COVID-19 vaccines will require careful safety evaluations for immunopotentiation that could lead to increased infectivity or eosinophilic infiltration. Besides this, a COVID-19 vaccine target product profile must address vaccinating at-risk human populations including frontline healthcare workers, individuals over the age of 60, and those with underlying and debilitating chronic conditions. Among the vaccine technologies under evaluation are whole virus vaccines, recombinant protein subunit vaccines, and nucleic acid vaccines. Summary: Each current vaccine strategy has distinct advantages and disadvantages. Therefore, it is paramount that multiple strategies be advanced quickly and then evaluated for safety and efficacy. Ultimately, the safety studies to minimize undesired immunopotentiation will become the most significant bottleneck in terms of time. In December 2019, a novel coronavirus pneumonia emerged in Wuhan, China, linked initially to animal-to-human transmission in local wet markets. Subsequently, human-to-human transmission of the virus commenced, resulting in widespread respiratory illness in Wuhan and other urban areas of Hubei Province, China. The coronavirus then spread across China and at least 20 other nations. On February 11, the World Health Organization named the virus SARS-CoV-2 and the syndrome was named COVID-19, or coronavirus disease 2019. Although not as lethal as the severe acute respiratory syndrome (SARS) outbreak in 2003, COVID-19 is still characterized by severe respiratory illness and significant mortality, especially among individuals over the age of 60 years and in those with underlying chronic conditions such as diabetes and hypertension. Moreover, SARS-CoV-2 is highly transmissible with an estimated reproductive number (R0) of 2.2, i.e., one infected individual is estimated to transmit the virus to 2.2 other individuals, and a mean incubation period of 5.8 days. The finding that SARS-CoV-2 is transmitted from infected individuals without symptoms, together with its ability to cause pandemic disease within a period of weeks, suggests that control of this viral infection will be challenging without the prospect of a vaccine. Here we provide a brief overview of some of the major candidates and the challenges of implementing vaccine strategies. Since much of the information about these vaccines has not yet entered the peer-reviewed literature, for this brief overview, we rely significantly on the information made publicly available on websites and other documents.