18 years ago, the world was introduced to a new type of threat – an international coronavirus outbreak. The first wave of its kind in the 21st century, Severe acute respiratory syndrome (SARS) quickly swept through many countries, causing international panic and threatening many of Asia’s economies. Affecting over 8000 individuals and leaving over 700 deaths in its trail, SARS was quickly contained by strict quarantining efforts and isolation of all exposed contacts (Wilder-Smith et al., 2020). SARS disappeared as quickly as it had appeared and served as a global warning to the possibility of another viral outbreak. So, how did the world respond to SARS?

SARS appeared first in Guangdong, China in November 2002 (Stadler et al., 2003). The virus was found to be airborne when a Doctor, who had been treating Chinese SARS patients under the belief that they were infected with Chlamydia pneumoniae, developed symptoms at a hotel in Hong Kong (Stadler et al., 2003). He was admitted to a hospital the following day where he succumbed to his injuries; however, the virus had been transmitted to guests of the hotel and carried back to their home countries (Stadler et al., 2003). The virus spread to many new regions, but was concentrated primarily in Hong Kong, China, Canada, Taiwan, and Singapore. A SARS infection resulted in fevers, breathing complications, and muscle pain (Stadler et al., 2003); these common symptoms were assumed to be the result of atypical pneumonia, which allowed the virus to evade detection by the Chinese Ministry of Health and the World Health Organization (WHO) for a few weeks (World Health Organization, 2021). However, on March 16, 2003, WHO declared SARS to be an outbreak and mobilized its Global Outbreak Alert and Response Network to provide support to Hong Kong (World Health Organization, 2021).

SARS is a part of the Coronaviridae family, also known as coronaviruses, and is more formally known as SARS-CoV-1 (Stadler et al., 2003). Coronaviruses are associated with respiratory problems, which cause the common cold-like symptoms seen in infected patients (Stadler et al., 2003). In addition, SARS is mainly spread through respiratory droplets (Zhou et al., 2020). Genomic sequencing of SARS was compared to three existing groups of coronaviruses. It was found that all three groups share two similar open reading frames, ORF1a and ORF1b, which are read by DNA machinery and translated into amino acids; however, SARS contains different sequences for many of its protein-encoding genes (Stadler et al., 2003). Analysis suggests that SARS may have descended from Group 2 coronaviruses, which includes the Mouse hepatitis virus, and continued to evolve due to the high mutation rate of RNA viruses (Stadler et al., 2003). Thus, it was concluded that SARS be classified as its own group (Stadler et al., 2003).

A further distinction was made between the genomes of strains from mainland China and from the Hong Kong hotel. Chinese mammals with SARS-like isolates and the strain from China shared a 29 nucleotide sequence found in an open reading frame, whereas the isolates from the Hong Kong hotel lacked this region (Stadler et al., 2003). Researchers hypothesized that the absence of this sequence may have allowed for more efficient transmission of the virus between individuals, after its initial leap from animals into humans (Stadler et al., 2003).

The virus primarily affected healthcare workers and individuals in close contact with victims, which allowed for more precise surveillance (Chan et al., 2011). Health officials focused on contact tracing and isolation of suspected individuals; in Toronto, Canada, quarantining took place in individual homes and designated hotels (Wilder-Smith et al., 2020). In addition, public health officials remained in touch with quarantining individuals, which allowed for very specific monitoring and quick action if symptoms developed (Wilder-Smith et al., 2020). This effort was aided by the fact that SARS became transmissible after symptoms had begun to appear, thereby allowing for earlier isolation and decreasing secondary transmissions (Wilder-Smith et al., 2020).

In countries such as Singapore and China, community-wide isolation was put into effect. Certain regions were designated as monitoring locations and public buildings were shut down, whilst citizens were asked to record their temperatures several times throughout the day (Wilder-Smith et al., 2020). Due to the knowledge of SARS and voluntary isolation, the number of affected individuals began to decrease fast in China (Wilder-Smith et al., 2020).

In addition, rises in temperature and humidity caused by the onset of summer may have aided in the decline of reported cases (Petersen et al., 2020). A research study found that virus viability was decreased at higher humidity and temperatures, which may provide an explanation as to why certain countries in Asia were not significantly affected despite their close proximity to China (Chan et al., 2011). The same study looked at virus viability in a regular air-conditioned setting, and found that a dried form of SARS could last over two weeks on a smooth surface if held at room temperature and humidity levels of 40-50% (Chan et al., 2011). As mentioned previously, a sizable portion of SARS victims were healthcare workers or individuals in contact with patients. These results may explain how the SARS could survive on non-living objects, such as furniture in a home, as well as be transmitted in healthcare settings through worker-surface or worker-object contact.

However, despite the international panic it caused, SARS was mostly contained within the span of eight months due to these strict quarantine measures (Wilder-Smith et al., 2020).

17 years later, the world began to face the threat of a new coronavirus, SARS-CoV-2, also known as COVID-19. After the introduction and experience with SARS, the public began to wonder how far public health measures have advanced and prepared for another viral threat? 

SARS and COVID-19 are both coronaviruses and share around 80% genome similarity, however it is important to note that the number varies depending on the research institute and sequences being analyzed (Zhou et al., 2020). In addition, both viruses are spread through respiratory droplets, use similar receptors for entry, and have been suggested to originate from bats sold in food markets (Wilder-Smith et al., 2020). Yet, despite their similarities, COVID-19 has caused more deaths worldwide and a prolonged quarantine period. So why has COVID-19 not been eradicated with the same efficiency as SARS?

Unlike SARS, which has an incubation period of 2-7 days, COVID-19 has an incubation period of 4-12 days, in which the occurrence of symptoms is not always guaranteed (Petersen et al., 2020). Furthermore, COVID-19 is transmissible during the symptomatic and asymptomatic phases of infection, which makes contact tracing more dependent on the estimated time of infection rather than post-symptomatic contact (Wilder-Smith et al., 2020). Estimated time of contact is not an accurate indicator of exposure and thus, gives a wide time interval in which a victim may have met multiple individuals. Asymptomatic transmission is a factor in explaining  how COVID-19 spread rapidly even as quarantining measures were introduced. 

In addition, Wuhan, the origin of COVID-19, is an industrial city with a large airport and train station, which allowed for faster transmission domestically and internationally (Wilder-Smith et al., 2020). Furthermore, there was greater awareness for SARS in the concentrated countries, whereas politics and media currently play a large part in downplaying the effects of COVID-19 . Therefore, the techniques used to contain SARS cannot be replicated with the same efficiency for COVID-19.

SARS was the first epidemic of its kind. Although it may not have allowed for a direct solution to handling COVID-19, experience with SARS helped many healthcare settings be more informed and prepared for future outbreaks. In addition, sequencing, diagnostic assays, and vaccine development were performed at a faster rate in 2020 than 2002 (Wilder-Smith et al., 2020). The world has advanced greatly since the SARS outbreak in terms of technology and medical knowledge; however we cannot disregard the possibility of another outbreak, or resurfacing event, after vaccines for COVID-19 start rolling out. As easily as we may have asked what we learned from our experience with SARS, we may just as easily ask how COVID-19 prepared us for another viral pandemic in the future.