Two infants are undergoing treatment in WA hospitals after they were diagnosed with meningococcal disease in the past fortnight.
One infant is in a serious condition at Albany Hospital, while another child is in a stable condition in Princess Margaret Hospital.
The Department of Health said the infant at PMH "is making a good recovery".
The two cases are not linked.
Nine infants in WA have been diagnosed with the infection this year.
Close contacts of both children have been given information and, where appropriate, antibiotics.
In NSW, a two-year-old boy from Port Stephens died this week after contracting the meningococcal infection.
Symptoms may include fever, chills, muscle and joint pains and a pale or blotchy complexion.