7.5.5: Coronaviruses- MERS, SARS, and COVID-19

Coronaviruses are a group of viruses that can cause upper-respiratory infections like the common cold, with symptoms like fever, cough, runny nose, and a sore throat. They are called coronaviruses because of how they look under a microscope: spikes on the surface give the virus a crown-like appearance. In some cases, coronaviruses can lead to severe infections like pneumonia and certain strains can cause significant morbidity and mortality. Coronaviruses are also zoonotic infections, and have been found in bats, palm civets, and camels. In fact, zoonotic transmission to humans is how the more severe coronaviruses such as SARS and MERS are thought to have first emerged.

Severe Acute Respiratory Syndrome (SARS) was a coronavirus first discovered in 2002 in China and rapidly spread to several countries, causing over 8,000 cases and 800 deaths. Yet the public health response was swift; and even though this severe illness had spread to over two dozen countries, the outbreak was brought under control within the following year (SARS and MERS, n.d.).

Middle East Respiratory Syndrome (MERS) emerged in 2013 in the Middle East, and was thought to have been transmitted from camels, who probably got it from bats. Although this disease was less easily spread between humans than SARS, it caused more severe disease and the mortality rate appears to have been much higher - around 35% of cases cause death (SARS and MERS, n.d.). Between April 2012 and January 2024, there have been 2609 lab-confirmed MERS cases, and 939 deaths - and the majority of cases have occurred in Saudi Arabia (WHO Eastern Mediterranean Region, 2024).

SARS-CoV-2 is the virus that causes COVID-19 illness, and began the worldwide pandemic in December of 2019. What made this virus able to spread across the globe so rapidly was its virulence: unlike SARS and MERS before it, the virus could be transmitted to other humans even when the infected person showed no symptoms. Although it seemed as though the mortality rate of the disease was relatively low and decreased significantly over the next 2.5 years, the disease caused over 1 million deaths in the U.S. alone during that time simply due to the large numbers of people it affected (SARS-CoV-2 and COVID-19, n.d., CDC, 2024c).

The pandemic also had a huge impact on other biological and social determinants of health. Healthcare systems were overloaded, healthcare staff were at high risk of contracting the disease - especially with shortages of personal protective equipment (PPE). Fears of catching the virus kept people from seeking healthcare for other issues like managing chronic diseases (SARS-CoV-2 and COVID-19, n.d.). Businesses and schools were closed, and job losses created huge economic (and health insurance coverage) impacts which hit the lowest socioeconomic tiers the hardest.

Vaccines for COVID-19 were soon developed and clinical trials were fast tracked during 2020. By the end of 2020 and beginning of 2021, vaccines were given emergency use authorization (EUA) by the FDA. Three vaccines were used in the U.S. - the Moderna and Pfizer vaccines were mRNA vaccines, and the Johnson & Johnson vaccine utilized a vector. All three vaccines were unique in that they did not carry a killed or attenuated virus - rather they used different mechanisms to provide information to the human body to create the unique spike protein on the surface of the virus. The body’s immune system could then recognize this spike protein and mount a defense against it. Although these vaccines were developed and tested in a far shorter time than expected, they built on research that had been going on for decades (National Institutes of Health, 2023).

The vaccines demonstrated high levels of safety and efficacy against the initial variants of SARS-CoV-2. As new variants emerged, it became clear that the vaccines were less likely to protect against infection completely, yet they still offered protection against severe disease, reduced hospitalizations, and even reduced viral load (which can potentially reduce transmission) (Oordt-Speets et al., 2023). It is estimated that vaccines prevented another 66 million infections and 2 million deaths (National Institutes of Health, 2023).

Vaccine hesitancy and misinformation also had an effect on vaccine uptake. Vaccine myths were perpetuated over social media and political venues, including proposals that the vaccines included microchips, made the vaccinated magnetic, affected fertility, or caused deadly heart problems in young males (CDC, 2023d, CDC, 2023e, CDC, 2023h). As of May 2023, over 81% of Americans had received at least one dose of the vaccine, and almost 70% had taken the recommended 2 doses. Subsequent booster uptake for new variants was significantly lower (CDC, 2023a).

Figure \(\PageIndex{1}\): Electron microscopic image of a negatively stained particle of SARS-CoV-2, causative agent of COVID-19. Note the prominent spikes from which the coronavirus gets its name for “corona”, or “crown-like”. (Copyright; CC0, CDC/ Hannah A. Bullock and Azaibi Tamin)

Electron microscopic image of a negatively stained particle of SARS-CoV-2, causative agent of COVID-19. Note the prominent spikes from which the coronavirus gets its name for “corona”, or “crown-like”. CDC/ Hannah A. Bullock and Azaibi Tamin