How did Sars start - and end?

The ongoing coronavirus outbreak, which has reached more than 110,000 cases worldwide, has prompted health experts to look back to past epidemics such as the Sudden Acute Respiratory Syndrome (Sars) infection of 2003.

During the Sars epidemic 17 years ago, 5,327 people on the Chinese mainland were confirmed to have been infected. This figure was overtaken by the new coronavirus outbreak at the end of January and the virus has now spread to 115 countries and territories.

The official name of the new virus - Severe Acute Respiratory Syndrome Coronavirus 2 (Sars-CoV-2) - was chosen because it is genetically related to the 2003 outbreak (officially Sars-CoV). But the World Health Organization (WHO) has said the diseases have unique characteristics.

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How did Sars begin?

The Sars virus originated in China in 2002. The NHS website reports that experts believe a strain “usually only found in small mammals mutated, enabling it to infect humans”.

WHO says Sars is thought to be an animal virus “from an as-yet-uncertain animal reservoir, perhaps bats, that spread to other animals (civet cats) and first infected humans in the Guangdong province of southern China”.

The infection quickly spread to other Asian countries and beyond, with a major outbreak in the Canadian city of Toronto, and a smaller number of cases in other nations, including four in the UK.

Sars affected a total of 26 countries, with 8,098 reported cases and 774 deaths. Those over the age of 65 were particularly at risk.

How did it end?

A raft of measures were taken to contain the outbreak. These included isolating Sars patients and quarantining people who had been exposed to the virus.

“Symbolised by the image of masked faces, Sars struck fear into the public across the globe, triggering drastic measures: mass quarantine in hospital wards enforced by armed guards, infectious passengers hauled off planes, and closed businesses and schools,” according to a WHO news bulletin published in the wake of the 2003 outbreak. “As the epidemic grew, China threatened to execute any Sars patient who violated quarantine.”

Then, after four months of fear, “as quickly as it emerged, Sars vanished,” says HuffPost.

The news site adds: “The virus hasn’t been seen since, leaving people to wonder: Where did Sars go? Was it truly vanquished? And might it ever return?”

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How do Sars and the new coronavirus compare?

Coronaviruses are a large family of viruses that cause illnesses from the common cold to more severe diseases such as the original Sars outbreak and now Covid-19, explains WHO. A “novel coronavirus” is simply a “new strain that has not been previously identified in humans”, it says.

“Covid-19 differs from Sars in terms of infectious period, transmissibility, clinical severity, and extent of community spread. Even if traditional public health measures are not able to fully contain the outbreak of Covid-19, they will still be effective in reducing peak incidence and global deaths,” according to a report published in The Lancet.

Many more Covid-19 patients have mild symptoms compared with those who had Sars, but this means that they can be easily missed and not isolated, contributing to further spread, says the report.

Last week, WHO said that “globally, about 3.4% of reported Covid-19 cases have died”, although the mortality rate depends on a range of factors, including age and general health. And because many people are experiencing mild symptoms, not all cases are reported, meaning that the rate of deaths per cases might be lower. The UK government says its “very best assessment” is “2% or, likely, lower”.

The first Sars outbreak, on the other hand, resulted in 8,098 reported cases and 774 deaths – meaning the virus killed about 10% of people who were infected.

However, Sars “usually didn’t become contagious until several days after symptoms appeared”, meaning that “actions taken during this period to isolate or quarantine ill patients can effectively interrupt transmission”, reports Bloomberg. But, with the new coronavirus, “it seems that it can transmit quite a bit before symptoms occur”, the site adds.