The national medical regulator says there is "limited evidence" that menstrual problems increase after women have COVID-19 vaccines and there is no evidence vaccines affect fertility.
The Therapeutic Goods Administration (TGA) recently looked into whether irregularities, problems or changes to women's periods had any link to the vaccines.
According to the TGA, it has received reports of problems from women under 50 about all three of the current vaccines on offer — with 11 reports per 100,000 people for Pfizer, 15 per 100,000 for Moderna and 20 per 100,000 for AstraZeneca.
Using overseas research and evidence, the TGA investigated the issue and found, given how common menstrual cycle issues were, there was only "limited evidence that [problems] increase after vaccination".
"Many factors can affect menstruation including stress, weight gain or loss, and underlying conditions like polycystic ovary syndrome and uterine fibroids.
"Changes to the menstrual cycle have also been reported after infection with COVID-19 and in people with 'long COVID'."
The TGA pointed to research done by leading medicines regulators in the UK, New Zealand and Europe which found no link between the two.
Its findings back up what international experts have said, highlighting that the stress of the pandemic may also be contributing to changes.
Whether the vaccines do play a role in changing women's cycles is something the TGA has been looking at for months, after first indicating it was investigating the issue last August.
At the time, it said it "did not find evidence" of any link but it would continue to monitor any reports.
Both last year and now, the most commonly reported symptoms are heavy periods, irregular or delayed bleeding and bleeding between periods.
The TGA repeated its call for any women who, after their COVID-19 vaccination, noticed a change in their period or had gone through menopause and experienced new vaginal bleeding to contact their doctor.
