The reason why a total of 55 young children in West Australia experienced febrile convulsions and a two year-old, Ashley Epapara found dead in her cot after receiving the seasonal flu vaccinations has left health experts perplexed but they hope to seek the root cause of the problem, by next week.

Jim Bishop, chief medical officer of the commonwealth had declared a suspension of flu vaccination for children under five late last week as a precaution, after an increase number of hospital admissions in WA over the past month.

All state and territory health authorities have been asked to report on any cases of acute illness following flu vaccination, in an effort to get the complete picture of the spread of cases, said Prof Bishop yesterday.

The samples of the flu vaccines used in WA are now being tested by the Therapeutic Goods Administration (TGA).

According to Prof Bishop and Ian Barr, international flu expert, it was unlikely the vaccines were responsible for any markedly different reactions from those triggered by slightly different vaccine strains of previous years.

The death of two year-old Ashley Apapara is now being investigated by the Queensland Coroner.

Flu vaccines trigger minor reactions like fever, swelling and headaches in nearly 10 per cent of the cases.