Pregnant women can safely receive COVID-19 mRNA vaccines, ending up with side effects less frequently than people who aren't pregnant, a Canadian study has found.

The study looked at how pregnant and non-pregnant women reacted to mRNA vaccines within a week after their second dose.

More than seven per cent of pregnant women felt unwell afterwards, having to take time off school, work, or seek medical attention because of symptoms like headaches or fatigue.

As for non-pregnant females, more than 11 per cent had to take time off or seek medical attention in the week after their second dose.

The study, published in The Lancet Infectious Diseases journal, looked at more than 180,000 women who received a first dose of an mRNA vaccine, and more than 94,000 who received a second dose.

Among them, nearly 5600 were pregnant for their first dose, and more than 3100 were pregnant for their second.

The study also included a control group of more than 6100 unvaccinated women, of whom nearly 340 were pregnant.

About three per cent of unvaccinated pregnant women reported similar health events like headaches or fatigue in a given week, lending weight to the possibility some of the vaccinated pregnant women's symptoms may not have been caused by a vaccine.

Researchers from the British Columbia Children's Hospital Research Institute were surprised by the findings, not expecting to see a lower rate of health events among pregnant women, versus people who weren't pregnant.

"Previous studies on other vaccines in pregnant women have mostly reported no significant differences in health events between pregnant and non-pregnant women or have found higher rates in pregnancy," senior study author Dr Julie Bettinger said.

"Further studies of non-COVID-19 mRNA vaccines are required to identify if the reduced side effects observed in pregnant people in this study is a feature of the mRNA vaccine platform, or of these specific vaccines."

The findings add to the growing body of evidence that COVID-19 mRNA vaccines are safe during pregnancy, researchers said. There was no major difference for "serious" health events across the groups.

Another US study has found healthcare systems should put extra resources towards dealing with COVID-19 patients for six months after their infections, because of ongoing effects of the virus.

The study, published by The Journal of the American Medical Association, looked at more than 250,000 people, half of whom tested positive for COVID.

It found people who tested positive used the healthcare system more in the six months after their infection than people who tested negative.

Most notably, people sought care post-COVID for conditions including alopecia, bronchitis, pulmonary embolism or deep vein thrombosis, and shortness of breath, according to the study.

LATEST 24-HOUR COVID-19 DATA:

NSW: 6979 cases, nine deaths, 2148 in hospital with 58 in ICU

Victoria: 3450 cases, 24 deaths, 575 in hospital with 29 in ICU

Tasmania: 375 cases, one death, 17 in hospital with two in ICU.