A private doctor developed Guillain-Barre syndrome (GBS) - a condition in which the body damages its own nerve cells, causing muscle weakness and even paralysis - after receiving a vaccination on Christmas Eve and felt leg weakness within two days.

A week later, he was admitted to Queen Mary Hospital in Pok Fu Lam.

Recent tests found no trace of bacterial or viral infections that could have caused the condition.

In the second report, a 91-year-old man who was vaccinated on January 4 was admitted to Princess Margaret Hospital in Lai Chi Kok on Tuesday for back pain, leg weakness, cough and flu symptoms.

Preliminary investigation shows the man is unlikely to have developed Guillain-Barr? syndrome.

He and the first patient are in stable condition.

Centre for Health Protection controller Thomas Tsang Hoi-fai said yesterday the centre could not establish whether the syndrome in the first patient, who is recovering, was caused by the swine flu vaccine.

'We could not establish a link or rule it out. We cannot make a conclusion by having just one GBS case,' Tsang said.

Former Hong Kong Medical Association president Choi Kin said the government should suspend the vaccination if the second patient was confirmed to have the syndrome.

'If there are two GBS cases out of 130,000 vaccinations, the safety of the vaccines is in doubt. I for one will stop vaccinating my patients,' he said.

But Tsang said the government had to evaluate whether the number of cases with the syndrome in the city had risen above the baseline of five or six a month before it reconsidered the safety of the vaccine.

The risk of contracting the condition from a flu shot was one in a million. Tsang said the government would consider suspending the scheme if there were more than four confirmed cases after the first round of 500,000 shots.

'We note the public sentiment but we have no magic bullet to change it overnight. Perhaps the winter flu peak will be an incentive for people to have the shot,' Tsang said.

The number of flu cases in the past two to three weeks was usually stable and the peak would probably hit around the Lunar New Year next month, when human traffic increases, he said.

'Instead of eyeing only one or two GBS cases reported, people should remind themselves that more than 50 people have died of swine flu so far, with another 200 people having suffered severe complications,' Tsang said. 'If the government hastily suspends the vaccination programme, it may deprive people of the chance to get protection.'

University of Hong Kong microbiologist Dr Ho Pak-leung said there was no scientific evidence to show the vaccine was unsafe. 'However, there is a growing suspicion among the community about the safety of the vaccine. The government is not facing a scientific question now, but a political one.'

Yesterday in Macau, on the sidelines of a meeting of senior health officials from the mainland, Hong Kong and Macau, Secretary for Food and Health Dr York Chow Yat-ngok said the government had no plans to shelve the vaccination programme.

'Guillain-Barre syndrome is uncommon among the elderly. We will be cautious and perform other tests to check his condition,' he said, referring to the 91-year-old man.

Chow said the government neither planned to transfer its stock of vaccines to other places nor demand a refund from the manufacturer because it had to ensure there were enough shots available to prepare for the winter flu peak. The vaccines do not expire until a year later.

Professor Yuen Kwok-yung, head of microbiology at the University of Hong Kong, said the vaccination programme should continue. 'More than 50 people have been killed by swine flu in Hong Kong but the risk of side effects of the vaccine is still very small. There should not be any undue alarm,' Yuen said.

Cheng Chi-man, a private doctor in Western district, said he had 100 people booked to receive the flu shot but after news of the first adverse reaction broke, only two turned up.

The Hospital Authority said that of the 107 swine flu patients still in hospital yesterday, 10 were in serious condition and 16 critical.