A serial liar is behind bars after she repeatedly pretended to be a nurse and injected patients with vaccines despite having no qualifications.

Alison Jane Mibus was sentenced in Adelaide Magistrates Court to four months and 28 days in prison after pleading guilty to falsely claiming to be a registered practitioner for a second time.

Magistrate Brett Dixon said any punishment short of jail time would be insufficient as the offending was "too serious and it would send the wrong message to the community".

In January 2019, Mibus falsely claimed to be a registered nurse with years of experience in an application for a job at an Adelaide medical clinic, despite the role not requiring her to be one.

She was fined $10,500 in February 2020 for pretending to be a nurse and administering vaccines at a different medical centre, where she had worked previously.

But the sentence did not bring Mibus' ruse to an end.

She continued to be employed at her new workplace, where she posed as a nurse in emails and administered vaccinations to a colleague and his parents.

In sentencing her on Tuesday, Mr Dixon said her repeat offending elevated the seriousness of her crime.

Her deception was only uncovered after she resigned from her position and her employer reported concerns to health regulator AHPRA.

"The nurse-patient relationship requires the utmost trust and anyone who abuses that faith should face the full consequences of their actions," AHPRA chief executive Martin Fletcher said.

"While this is a strong outcome, it is disappointing this individual didn't learn her lesson last time.

"Hopefully this outcome is the final deterrent."

The case is the first time a person has been sentenced to prison in Australia for falsely claiming to be a qualified nurse.

Nursing and Midwifery Board of Australia chair Veronica Casey hopes the outcome serves as a warning to anyone considering lying about their qualifications.

"Being able to call yourself a nurse in Australia means something, and for someone to knowingly represent themselves as one to secure a job not only discredits the hard work and commitment of the profession, but is a criminal offence," she said.

"Employers are also reminded to ensure their employees are registered when they say they are and are not misleading patients, colleagues or authorities.

"It is putting the public at risk of harm."

Mibus was ordered to pay AHPRA $1628 in legal costs and will be eligible for release from prison after one month.