The exposure to last year's swine flu outbreak may have caused children to be more susceptible to experiencing severe reactions that are now manifested through recent influenza vaccinations.
That is one of the theories as to why more than 250 children in WA have been admitted to the hospital for experiencing adverse reactions after being inoculated with the seasonal flu vaccine.
The death of two year-old Ashley Epapara, has also been associated with bad reactions toward the vaccination.
To date, a total of 55 children had been reported to experience febrile convulsions after getting vaccinated while an additional 196 suffered less serious reactions such as fever and vomiting.
According to an infectious diseases expert at the Australian National University, Professor Peter Collignon, a possible theory could be that the children's exposure to swine flu last year could have made their immune system to react aggressively to an injected dose of the vaccine that includes the strain of H1N1.
However, Professor Terry Nolan of the University of Melbourne who conducted the research into children's reactions to swine flu vaccine last year, said the theory seemed unlikely as the children did not exhibit more severe reactions to the second of the two injections given last year.
The deputy director of the National Centre for Immunization Research and Surveillance, Kristine Macartney said more reactions were reported in Western Australia because it was the only state to have a policy of immunizing all children under five with the seasonal flu vaccine.
Western Australia are immunizing many more young children than other states and territories, where children are only recommended to have the vaccine if they are in a high-risk group, she said.
After receiving immunization, she observed that up to 40 per cent of children will develop elevated temperature and 3 per cent of children will have febrile convulsions at some stage.
Senior research fellow at the centre, Julie Leask, who specializes on social responses to immunization, said it was perfectly understandable that parents and the medical community were worried about the vaccine's undesirable side effects.