TORONTO (BLOOMBERG) - Covid-19 vaccines using messenger RNA technology are safe in pregnancy, according to a large Canadian survey, further building the case for pregnant women to get the shots.

Vaccinated women who were not pregnant reported higher rates of potential side effects than pregnant women, surprising researchers.

In the survey, 7.3 per cent of pregnant women who got an mRNA-based Covid shot reported potential side effects within a week after their second dose, most commonly feeling unwell, having a headache or migraine or a respiratory tract infection.

About 11 per cent of respondents who were not pregnant made similar reports.

Further research is needed into future mRNA vaccines to show whether the reduced side effects in pregnant women were due to the mRNA vaccine platform or potentially a feature of these particular shots, said Dr Julie Bettinger, a vaccine safety scientist at the British Columbia Children's Hospital Research Institute, and the study's senior author.

Pregnant women face an elevated risk of severe Covid-19, and infections during pregnancy have been linked to a higher risk of complications.

The Canadian team focused on health outcomes within the first seven days after vaccination, though researchers said they were continuing to follow up on the findings.

Some 191,360 women completed a survey after their first vaccine dose, and 94,937 completed a survey after the second dose.