Getting any type of vaccination is a big decision when pregnant – but the more data we have the better informed we can be.
Unfortunately, around 75% of COVID-19 vaccine trials have excluded pregnant people, precluding them from the potentially life-saving benefits of vaccination. Because they were not part of clinical trials, there is not enough evidence around their safety and efficacy, which heavily impacts the decision to receive a vaccine.
“In a pandemic, where there’s a sense of urgency around getting important efficacy and safety data, we want that [data] in pregnant women as early as possible,” says Associate Professor Michelle Giles, an infectious diseases physician and specialist in maternal immunisation at Monash University. “If they’re not included in the original trials, there is a significant delay in getting that information.”
Historically, clinical studies and drug testing have been conducted primarily on men, even though women’s physiology and disease pathology may differ beyond just their reproductive organs.
For decades, the default human model for clinical research has been a 70 Kg male. Researchers have opposed efforts to include women in clinical research, arguing that their hormonal cycles complicate experiments.
Pregnant people have been systematically excluded from clinical trials because of safety concerns about exposing mother and unborn baby to experimental treatments. After all, there is evidence that some drugs can cross the placenta and affect the baby.
Less scientifically, including pregnant people in a trial can raise costs and make ethical approvals more challenging, and so they have been excluded for practical reasons.
As a result, drug side effects that may preferentially affect women have often not been discovered until after marketing approval, and this is even more so for pregnant people.
COVID-19 vaccine trials have been no different.
“When we make recommendations about who should receive vaccines, we take into account information from the clinical trials about how safe vaccines are, what their rate of side effects are, and how well they work,” says Professor Giles.
The lack of data does not mean vaccines are unsafe or don’t work, she explains, “But we don’t have that information available to provide pregnant to women so they can make an informed decision about whether to receive it or not.”
Initial clinical trials give us a glimpse into vaccine safety anyway, because Although participants were asked to avoid becoming pregnant, 57 got pregnant while participating in either Pfizer, Moderna or AstraZeneca trials.
Encouragingly, there was no significant difference in adverse pregnancy outcomes in the vaccinated groups compared with the control groups.
Some of the ongoing clinical trials have changed inclusion criteria, allowing pregnant people to be included in the trials.
But another way to obtain efficacy and safety data is through post-marketing surveillance.
In a study published recently in the New England Journal of Medicine, researchers followed over 35,000 pregnant people who received an mRNA vaccine in the US. They found that injection-site pain was more frequent in pregnant people than non-pregnant, but other mild adverse reactions were less frequent. Importantly, adverse pregnancy and newborn outcomes were no different to pre-pandemic clinical trials.
Although the data are still sparse, they are reassuring.
In Australia, COVID-19 vaccines are not routinely given to pregnant people. That does not mean that you can’t or should not get the vaccine if you are pregnant, says Professor Giles.
“Consideration should be given to two broad groups of pregnant women. Women that have coexisting medical conditions that put them at risk of severe disease are more likely to be admitted to intensive care or have a preterm birth if they get COVID-19. The other group are women who are more likely to be exposed to COVID-19, such as someone who works in hotel quarantine.”
Information and decision guides can be found on the Australian Government Department of Health website for people who are pregnant, breastfeeding, or planning pregnancy.
Professor Giles advises that pregnant people should talk to their health care provider about their risks versus the benefits of getting a vaccine.
“At the moment, there is low or no community transmission, so there is a low risk of being exposed,” she says. “But we know that it can change very quickly.”
Dr Manuela Callari is a Sydney-based freelance science writer who specialises in health and medical stories.
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