Precautions at Toronto hospitals since last month's SARS (search) outbreak failed to prevent dozens of possible new cases, health officials conceded Monday as the World Health Organization (search) put Canada's largest city back on its list of SARS-affected places.

The WHO designation is routine for transmission of new cases of severe acute respiratory syndrome, and a spokesman for the U.N. agency said Toronto was nowhere near another WHO warning against travel to the city.

Elsewhere, the number of new cases reported in China was down to eight, while Taiwan (search) reported 15. The health chief for Taiwan's capital resigned to take responsibility for a SARS outbreak at a hospital.

Hong Kong (search) researchers said a SARS vaccine developed with their mainland Chinese counterparts was ready for testing on animals, with results expected in six months.

In Toronto, health authorities scrambled to limit any further possible spread while investigating how eight probable new cases and 26 suspected cases slipped through upgraded monitoring and reaction systems designed to catch SARS.

The new cases included two deaths, and another death of a patient sick for months raised the overall toll in the Toronto area to 27 from more than 150 cases in the biggest SARS outbreak outside of Asia.

Toronto was removed from the WHO list of SARS-affected areas on May 14, after more than 20 days passed since the date of the last known case, on April 19. The new cluster is believed to come from an elderly patient whose case dates back to April 19.

The 96-year-old man developed pneumonia after surgery in an orthopedic ward at North York General Hospital. He turned out to have undiagnosed SARS and infected health care workers, other patients and visitors on the ward, officials said. A patient transferred from the orthopedic ward to St. John's Rehabilitation Hospital was considered the likely source of four more cases under investigation, they said.

The outbreak prompted the U.S. Centers for Disease Control (search) to issue a travel alert for Canada last week, a step short of advising against unnecessary travel there.

WHO officials stressed there were no plans to reinstate a travel advisory for Toronto. That requires specific criteria such as proven export of the illness. The agency imposed a travel advisory on Toronto on April 23 but lifted it a week later when Canada promised to upgrade monitoring of international travelers.

In response to the new cases, health authorities re-imposed strict controls on Toronto-area hospitals — closing those where the new cases were found to new patients, limiting access to emergency rooms in all others, with staff required to wear protective masks and gowns and take the temperature of anyone entering.

More than 2,000 people possibly exposed to the illness have been told to quarantine themselves at home for 10 days, said Dr. Colin D'Cunha, Ontario's chief medical officer of health.

The new Toronto cases showed that so-called "new normal" guidelines for dealing with potential SARS cases at hospitals, imposed after the initial outbreak, needed upgrading, officials said.

"What it tells us at the moment is that there is a failure in our system of management," said Dr. Allison McGeer, head of infection control of Mount Sinai Hospital who has recovered from SARS she contracted in the early days of Toronto's initial outbreak in March.

Dr. Paul Gully, a federal health official, called the new cluster unexpected and a cause of concern, but said visitors to Toronto have little to worry about because the illness remains isolated in hospitals that are closed to new patients.

"We still need to figure out how this happened," Gully said, adding that the "new normal" diagnostic guidelines for identifying possible SARS cases left room for error.

"It is a difficult judgment call" to distinguish a SARS case from the preponderance of respiratory illness cases that appear, he said.

The Toronto deaths, along with one in Hong Kong and three more in China, brought the worldwide death toll to 724. More than 8,100 people have been infected since the disease emerged in November, apparently in China's southern Guangdong province.

In Taiwan, the Taipei health chief, Chiu Shut-ti, took the blame for last month's SARS outbreak at the capital's Hoping Hospital by resigning Sunday night. The facility was the source for most of the island's SARS infections.

Chiu, known as an iron lady for her dedication to work and swift action, offered to quit soon after the city-run hospital was sealed off April 24 to contain infections. But Mayor Ma Ying-jeou asked her to stay. Chiu offered to resign again, saying the timing was right because the Taipei outbreak was coming under control, and Ma accepted.

On Monday, two Japanese doctors arrived to study why SARS spread so quickly in Taiwan — an economically developed society similar to Japan's. Japan has no confirmed SARS cases but is concerned the virus will hit there next.

Singapore asked Monday that any illegal immigrants showing SARS symptoms come forward. They would be sent home but not charged under the city-state's strict immigration laws, Home Affairs Minister Wong Kan Seng said. No illegal immigrant has yet been found with SARS, Wong said.

The education ministry also told students to bring thermometers to their exams next month. Separate rooms will be set aside for students with mild fevers or who have returned from SARS-affected countries, the ministry said Monday.

Visitor arrivals fell by 73 percent in the first three weeks of May, but the city-state's tourism chief predicted Monday that business will recover in June if there are no new SARS cases.