Scientists last year predicted SARS would return to infect thousands more people during the colder months in northern Asia. But the disease, which killed about 700 people in 2003, appears to have infected just four people in the past few months.
Governments across Asia have spent millions of dollars to prepare for a resurgence of Severe Acute Respiratory Syndrome.
Places such as Hong Kong and Singapore upgraded their health care systems, ran public hygiene improvement campaigns, and instituted mass health checks on travelers.
Last year, the new disease spread quickly to 8,000 people globally, killing about 700, most of the cases and deaths occurred in mainland China and Hong Kong. Part of the problem was that doctors knew nothing about the virus and were unprepared to stop the outbreak at its start.
But this year, SARS has not come back to infect thousands of people, as many scientists predicted it might in the colder months, when respiratory diseases are common. Some health officials say the preventative measures have worked, denying SARS a chance to spread.
Julie Hall, a health expert with the World Health Organization in Beijing, says the four cases that arose in China's Guangdong province in December and January were detected and isolated quickly.
"The system there is far stronger than it was last year," she explained. "We are able to pick up small numbers of cases and ensure that they don't become large numbers of cases."
Dr. Hall says that isolating the victims and the people they are in close contact with is key to beating SARS.
But other health experts argue isolation and better hygiene cannot explain why those four SARS patients this year were less ill and recovered faster than patients last year. Some say the virus from last year may have changed to become less aggressive. Others say the more dangerous strains could have become dormant this year.
David Hui is a doctor and researcher at Hong Kong's Prince of Wales Hospital. He works in the ward were SARS started spreading rapidly among health care workers a year ago.
Dr. Hui suggests the four patients in southern China apparently had a milder and less contagious strain of the SARS virus. Most of last year's patients spent weeks or months hospitalized, many of them in intensive care.
"The degree of the illness this time in southern China is very mild compared to the cases last year," he said. "For example among the four cases diagnosed and confirmed in Guangdong, all these cases only require a short period of supplemental oxygen and none of them progressed to the severe respiratory failure."
Dr. Hui says not only did the patients recover from the disease quickly, they also did not pass the virus on to anyone.
He says that last year each SARS victim, on average, infected at least two people.
Dr. Hui says it is too early to draw conclusions about SARS infections this year.
For example, he says, evidence suggests that there were at least four strains of the SARS virus affecting patients last year in Hong Kong. Scientists in China have not yet published their research on the recent isolated cases - so comparisons are not yet possible.
Dr. Hui says that China has also done a good job of eliminating the possible reservoirs of the virus in live animal food markets by culling thousands of animals that are known SARS carriers.
However, Julie Hall with the WHO says the experience with the infectious disease, ebola, in Africa, shows that while animals play a role in disease, eliminating them does not necessarily reduce the risk of the illness.
"Some like ebola, jump from animals to humans," said Dr. Hui. "And then it went back to the animals and it was there for quite a few years before it came back."
She says the scientific world is divided on whether slaughtering animals known to carry the disease actually eliminates the virus reservoir.
This is because animal to human transmission of an emerging illness does not follow a particular pattern. She says other factors, including the conditions in which animals are farmed, handled or prepared for cooking may encourage animal to human transmission of disease.
She added that environmental conditions such as floods, unusual temperatures, bad harvests and the number of displaced people can influence whether a particular virus gains prevalence.
