What came before? Comparison with other coronaviruses (MERS/SARS)

In week 1, we covered the Great Influenza pandemic of 1918 and what we have learned since. As you will almost certainly have been aware before this course, the current pandemic is caused by a coronavirus, but this is not the first coronavirus outbreak in recent times. Severe acute respiratory syndrome (SARS) and Middle East respiratory syndrome (MERS) were discovered in the first and second decades of this century, respectively.

The first reported cases of SARS were in Foshun, China in November 2002. By February 2003, more than 300 cases had been reported with over a third of those in healthcare workers. By April 2003 WHO-led efforts had identified SARS-CoV as the causative agent of the disease. Owing to the infection control measures put in place, no further cases were identified after July 2003. Overall the pandemic ended with 8096 reported cases and 774 deaths across 27 countries.

MERS was first identified in June 2012, following the death of a man in Saudi Arabia from acute pneumonia and renal failure. In contrast to the SARS timeline, MERS-CoV was isolated from the sputum of this index case, demonstrating the advances in pathogen genomics during the intervening years. There was a cluster of travel-related cases in the UK in September 2012 and in 2015 a hospital related (nosocomial) outbreak in South Korea involving 16 hospitals and 186 patients, but the overwhelming majority of cases were observed in Saudi Arabia. As of January 2020 there had been 2,494 laboratory confirmed cases notified to WHO across 27 countries and resulting in 858 deaths.

Similarities between these two coronavirus outbreaks include the likely zoonotic origin (potentially from civets in a wet market for SARS and dromedary camels for MERS), and the high percentage of nosocomial cases involving both patients and healthcare personnel. This is likely due to the late peak viral shedding observed around 10 days after onset of infection, at which time individuals had already been hospitalised.

However, the case fatality rate was different in both pandemics – ~10% for SARS and ~36% for MERS. In the current pandemic, the unprecedented amount of testing, surveillance and tracing has led to a far greater ascertainment of cases. Despite the current case fatality rate being significantly lower than that of SARS and MERS, the absolute number of deaths is much higher, due to the global spread of SARS-CoV-2.

These previous coronavirus pandemics provided both genomic and clinical guidance in the early stages of the current pandemic.

In Figure 1, you can observe a timeline of previous pandemics and public health emergencies in history. The death toll of SARS-CoV-2 is significantly higher than the previous coronavirus epidemics SARS-CoV-1 and MERS. Learn more about the history of pandemics in this article from Visual Capitalist.

Figure 1 – History of pandemics timeline. Source: Visual Capitalis.