The coronavirus that caused the 2003 SARS epidemic disappeared mysteriously over time but

Some people question why the current coronavirus has brought the world to standstill while a previous deadly coronavirus SARS did not.

SARS, which killed about 1 in every 10 people turned out to be highly lethal but ultimately, and somewhat mysteriously, disappeared.

The tale of SARS and its new cousin that causes Covid-19, SARS-CoV-2, shows just how unpredictable viruses can be, particularly when they jump from animals to humans.

SARS was first noted in Guangdong province in China in November of 2002, when doctors there saw an unusual pneumonia. But the disease was not reported to the World Health Organisation at that time. In February 2003, another outbreak occurred in Hanoi, Vietnam, and a World Health Organisation officer, who later died, examined a patient there and reported a large outbreak to the WHO main office on March 10, 2003.

Meanwhile, a doctor from Guangdong province travelled to Hong Kong and stayed at the Metropol Hotel along with a number of other international travelers. The doctor was infected with what we now know as SARS-CoV-1. The virus was transmitted to at least a dozen other hotel guests.

Two returned to Canada and took the virus there. One returned to Ireland, one to the United States. Three went to Singapore and one to Vietnam. In addition, a few people were hospitalised in Hong Kong, leading to an outbreak in the hospital there.

In all there were just over 8,000 cases of SARS-CoV-1, and about 700 deaths. In the United States, there were a total of just 29 confirmed cases and no deaths. The Hong Kong economy, with a large tourism component, was severely impacted by SARS in 2003, much as the US tourism industry is currently one of the most heavily impacted parts of the economy due to SARS-CoV-2.

SARS-CoV-1 and SARS-CoV-2 are closely related viruses. Scientists believe that both viruses originated in bats. The RNA genomes of the viruses are about 80% identical. What does that mean? Our own genomes are over 98% identical to those of chimpanzees, so 80% seems a lot less similar. For a virus though, especially one with an RNA genome, this is actually very closely related.

Tracking someone infected with the SARS-CoV-1 was relatively easy: Everyone had severe symptoms in two to three days.

With SARS-CoV-2, it takes about two weeks for symptoms to appear, and many people don’t have any symptoms at all. Imagine asking someone whom they had contact with for the last two weeks! You can accurately remember most people you had contact with for the past two days, but two weeks? This critical tool for pandemic control is very challenging to implement. This means that the only safe thing to do is to maintain quarantine of everyone until the pandemic is under control.

SARS vaccine? Vaccine studies for SARS-CoV-1 were started and tested in animal models. An inactivated whole virus was used in ferrets, nonhuman primates and mice. All of the vaccines resulted in protective immunity, but there were complications; the vaccines resulted in an immune disease in animals. No human studies were done, nor were the vaccine studies taken further because the virus disappeared.

Many factors were involved in the end of SARS-CoV-1, perhaps including summer weather, mutations, and certainly strict quarantine of all those who had contact with infected individuals, but we don’t really know why the epidemic ended. Viruses are like that – unpredictable.