The State Government has suspended its free flu vaccine program for WA children aged under five after 22 children became ill and were taken to Princess Margaret Hospital within hours of having their injections.
Health Minister Kim Hames said the otherwise fit and healthy children had suffered febrile convulsions - which involved a fit or seizure due to high fever - within 12 hours of having their vaccine.
The presentations at PMH were over the past month and it was still unclear if the vaccine was the cause, but at least one child was understood to have become seriously ill.
There have been no reports of other States reporting an unusually high number of side effects in children.
Dr Hames confirmed health authorities had closed the free vaccination program for young children as a precaution until tests could be carried out to see if the vaccine was responsible for the spike in reactions.
In the meantime, doctors and parents were being advised against having children aged under five vaccinated. The Health Department was last night trying to alert medical practitioners around the State, particularly GPs, to prevent any more vaccines being given out today.
The vaccine covers the human swine flu, as well as two other strains of seasonal influenza expected to circulate this winter, and has been given out to thousands of Australian children since mid-March.
WA is the only State to offer a free flu vaccine to children under five.
The Health Department said there were no concerns for children vaccinated days or weeks ago because if a child was going to have a reaction it would happen in the first 12 hours.
If children had received the vaccine just in the past 12 hours, parents were advised to give paracetamol according to the instructions on the bottle to help prevent a reaction occurring.
"At this stage the link is unclear but certainly there could be a risk to children so we're advising parents planning to go to their GP to have their young children vaccinated to hold off until we get more information," Dr Hames said.
"Febrile convulsions are not necessarily serious, and we don't want parents to panic but it is a concern. While this number of children is not necessarily huge, linked to these circumstances our experts do believe it's a significant number and there is a risk in WA.
"It may be an over-reaction on our part but it's better to be ultra- cautious."
Dr Hames said there were no reports of spikes in adverse reactions in other States which raised the possibility of a faulty batch of vaccine in WA but this needed to be investigated. With the coming long weekend, it could take several days.
He said there were no concerns for older children and adults who had recently received the flu vaccine.
Parents can get more information by ringing 1800 022 222.