(CNN) Nearly two decades after he was treated, former severe acute respiratory syndrome (SARS) patient Alex Lam is still haunted by his experience.

"(It is) painful hearing the news again. SARS is coming back, the deadly virus is coming back," he said. SARS , of course, has not returned, but a new type of deadly virus from the same family is sweeping China, opening old wounds for some.

In 2003, SARS infected more than 8,000 people, and killed 774. Asia was hardest hit, with Hong Kong recording almost 300 deaths. Lam was treated in an isolation ward for three weeks, and considered one of the lucky ones because he was discharged with no further complications.

"I was put in a big room with many other patients," he recalled. "I heard some coughing at night, crying, and that's really sad."

The novel coronavirus , which has now spread to at least 27 territories outside mainland China, is already bigger in numbers -- at least 28,000 people have been infected worldwide and more than 560 have died. The World Health Organization (WHO) has declared the outbreak a public health emergency of international concern , prompting countries to take unprecedented measures.

John Nicholls, clinical professor of pathology at the University of Hong Kong (HKU), said the SARS outbreak was brought to an end in July 2003 by good hygiene practices -- such as frequent hand-washing -- and environmental factors such as high temperature and humidity in the summer months.

"That will be the same for this one," he said. "My feeling is that this is just going to be like SARS and the world is going to get basically a very bad cold for about five months."

People wearing face masks as a preventative measure following a coronavirus outbreak which began in the Chinese city of Wuhan, line up to purchase face masks in Hong Kong on February 5, 2020.

Containment

ordered a To stop the virus spreading further, China hasordered a lockdown on the movement of millions of people, which has seen flights, trains and buses canceled in all major cities of Hubei province, where the coronavirus was first reported. School in Hong Kong and Macao -- semi-autonomous Chinese cities that operate their own education systems -- is suspended until at least March

Some countries, such as South Korea and the Philippines, have closed their borders to visitors arriving from mainland China. Others have also issued travel warnings and evacuated citizens in Wuhan.

Despite the drastic measures, some virology experts believe containing the current outbreak might prove to be more difficult than it was to stem SARS.

John Nicholls, clinical professor of pathology at the University of Hong Kong with CNN's Kristie Lu Stout.

Nicholls said one problem could be that the new virus appeared to have greater transmissibility than SARS, due the possibility that cases can be transmitted by asymptomatic patients.

The WHO, however, has said that "the main driver of transmission ... is symptomatic cases." The organization said that it was "aware of possible transmission" from asymptomatic individuals in a few instances but believed this to be rare and not a major player in the spread of the virus.

Meanwhile, Gilead Sciences, a biopharmaceutical firm with an experimental drug called remdesivir that is used to treat the Ebola virus, is working with Chinese health authorities to see if the medication can combat the symptoms of coronavirus.

Understanding the virus

In January, Nicholls and his team became the first scientists outside mainland China to reproduce the virus in a laboratory. They have since been studying it to understand how the coronavirus interacts with human tissue around the body, and evaluate the test that diagnoses patients.

Malik Peiris, a public health virologist at HKU who advises the WHO, said one optimistic sign was that the novel coronavirus appeared to have a lower fatality rate than SARS. On Tuesday, China's National Health Commission said the death rate was 2.1% nationwide, while SARS had a global ratio of 9.6% , according to the WHO.

Malik Peiris, a public health virologist at the University of Hong Kong and WHO adviser.

"The case fatality rate doesn't count the milder cases that don't come to medical attention -- and there does seem to be quite a number of those," Peiris said. "Hopefully, the severity of the disease is much lower than what we believe or what is apparent at the moment, and so the overall outcome may not be as dire as what some people think at this point in time."

Other medical scholars have given different predictions on how long the outbreak may last.

Zhong Nanshan, one of China's leading respiratory experts and a hero of the 2003 fight against SARS, said he expected the virus to peak as quickly as the coming weekend

Gabriel Leung, HKU's chair professor of public health medicine, was less optimistic and estimated the number of cases to peak around mid-April or mid-May.

The new normal?

Another scenario is that the new coronavirus could become a common global illness, like influenza. That outcome would not be without precedent. H1N1 -- a strain of flu responsible for the 2009 flu pandemic has now become a seasonal virus.

"The common cold is caused by two different types of coronaviruses," Peiris said.

For Lam, the former SARS patient, that scenario would be a failure. He is now the head of Hong Kong SARS Mutual Help Association -- a group of SARS survivors which is calling on the Hong Kong government to take tougher measures to end the outbreak.

"We hope that the government can do something more drastic ... because most parts of China are considered high risk," he said.

Lam also called for unity.

"To fight against contagious disease, we must stand together. We must not panic," he added. "We need to think positive, because one day, the disease will go away."