Christina Hartmann Benz, 51, was allegedly observed by a doctor last month failing to administer a shot to a teen who she knows.

It was alleged the registered nurse, who worked at a private medical centre in St James, inserted the needle into the teenager's arm but didn't push down on the plunger.

She was accused of disposing the full syringe and making a false entry in the medical records system, which recorded that another medical centre staffer had administered the dose instead of her.

Police further alleged the woman had obtained approval from her employer to administer the vaccine to people she knew at the clinic.

The medical centre reported the alleged breach to WA Police and Benz was arrested at her Byford home before being charged with one count of gaining benefit by fraud.

During a brief hearing in Perth Magistrates Court on Tuesday, it was revealed the charge had been discontinued.

The court awarded Benz $1500 in costs.

"Officers from the Breach Investigation Team conducted further inquiries into the matter," a WA Police spokesman said.

"As a result of those inquiries, further information was obtained and it was deemed there was insufficient evidence to continue a prosecution."

Benz and her lawyer declined to comment outside court.

Australian Associated Press