Inoculation has been proven to be useful in preventing flu outbreaks, Secretary for Food & Health Dr York Chow says, adding patients in all fatal and severe human swine flu cases were not vaccinated.

Dr Chow today told reporters the Government stockpiles human swine flu vaccines because it wants to ensure it has sufficient supply for all who may need it.

"Obviously we have sufficient supply for all five at-risk groups in Hong Kong, plus some extra for people who are willing to take the vaccine. I am not worried it has not [been] taken entirely because [if the influenza peak gets] worse, I am sure more people will be interested [in taking] it," he said.

"It is important we have it in reserve and can use it [during] the peak if necessary. It is like insurance. It is something you put there in case of need."