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INTRODUCTION

In late 2019 a cluster of pneumonia cases of unknown cause was reported from the city of Wuhan, China in Hubei province. A novel coronavirus designated SARS-CoV-2 was determined to be the cause which subsequently spread world-wide causing the COVID-19 pandemic. The first wave of the pandemic, as of this writing, is still underway. As of the beginning of August, 2020, documented cases reported to the World Health Organization (WHO) have reached nearly 18 million globally with the largest number of cases in the United States and SARS-CoV-2 deaths are reported to be nearly 687,000 worldwide. The virus has spread to nearly all parts of the globe but the burden of disease has varied widely both within and among countries. Given that the pandemic is evolving on a daily basis, this chapter presents a snapshot of the situation which will change with the passage of time. Because of the novel nature of this virus, it is not possible to predict with any degree of certainty how the epidemiology of the pandemic will progress in countries around the world.

As SARS-CoV-2 emerged, many looked to recent examples of novel coronavirus emergence and influenza virus pandemics for guidance. The related coronavirus, SARS-CoV, for example, emerged in 2002, spread in 2003 to a small number of cities globally and then rapidly disappeared. There was no second wave associated with SARS-CoV and the virus did not cause a pandemic. Another novel coronavirus, MERS, has caused sporadic outbreaks but seems to be limited in terms of human-to-human transmission. In contrast, novel influenza viruses have caused four pandemics in the past 100 years, and have always produced several waves of disease before transitioning to seasonal viruses. While it is not possible to predict the path this virus will follow, most experts believe it will not simply disappear.

The most difficult related issue to predict is the speed with which vaccines and therapeutics for SARS CoV-2 might be developed. These will potentially play a key role in controlling the virus in the future, and it is only possible to discuss in general terms what their impact on the pandemic might be. Four other coronaviruses have been recognized in the population for years and they will be discussed as background to the three that have resulted in severe disease.

The Outbreak Begins

As with most pandemics, there is little certainty about the precise origins of the causative SARS-CoV-2. For reference, the precise locale where the 2009 pandemic influenza virus moved from swine to humans is not known, although it is generally acknowledged that the first outbreaks were detected in Mexico. Similarly, the SARS-CoV virus seems to have originated in bats but the host from which it moved to humans in Guangdong in 2002 is debated. The related SARS-CoV-2 virus appears also to have had a bat origin but how and exactly when it established human-to-human ...

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