mRNA COVID-19 vaccine: Should pregnant women receive it if it’s first to market?
****THIS IS NOT AN UP-TO-DATE RESOURCE FOR COVID-19 VACCINES IN PREGNANCY. This article was written prior to the mRNA vaccines being approved and prior to safety data. It is now deemed SAFE and EFFECTIVE to receive the mRNA COVID-19 vaccine in pregnancy***
****THIS IS NOT AN UP-TO-DATE RESOURCE FOR COVID-19 VACCINES IN PREGNANCY****
In Nepal, public health officials are seeing record rise in stillbirths from the lack of antenatal care as the country went into lockdown. In the United States, contracting COVID-19 while being pregnant has been associated with an increased risk in ICU admission and being placed on mechanical ventilation. It is clear that COVID-19 disproportionately impacts pregnant patients compared to non-pregnant patients.
As we eagerly wait for a vaccine, it is important to discuss if pregnant women will be left behind as none of the current vaccine trials include pregnant women as part of their study.
One of the most popular and promising vaccines undergoing Phase 3 clinical trial is Moderna’s mRNA vaccine. mRNA-based vaccines have never been studied in humans prior to the onset of the pandemic. Typically, pregnant patients are encouraged to receive inactivated vaccines, such as the annual flu vaccine because of demonstrated safety, while live-attenuated vaccine like those for MMR and varicella are avoided due to potential for infection.One of the main questions I had during my OB/GYN rotation as a pharmacy student was how do mRNA vaccines work and will they be safe in pregnancy? Do they act more like an inactivated vaccine or a live-attenuated vaccine?
It turns out, neither.
What is the mechanism of action of mRNA-based vaccines?
In a nutshell, mRNA vaccines work by providing our cells with a recipe to create the proteins necessary to mount an immune response. Here is a short visual video produced by Moderna:
An mRNA-based vaccine was a pipe dream for a long time. Difficulties in getting the mRNA to survive after an injection and difficulties in getting cells to accept the mRNA have kept this technology out of reach. However, advances in the last decade in encapsulation technology have allowed scientists to create clever ways to safely deliver mRNA sequences to cell cytoplasm. Fast sequencing methods have also made this an extremely appealing method for designing vaccines quickly, especially in a pandemic.
So, will it be safe in pregnancy?
Very little is currently known about the safety of mRNA-based vaccines in pregnancy. During the height of the Zika virus in 2017, Moderna developed a Zika vaccine and tested it in mice. They found that the mRNA based Zika vaccine was able to provide immunity to their baby mice, but the mice-mom must receive the vaccine before she was pregnant. This was the only direct data that included pregnancy in any mRNA-based vaccine.
The mRNA itself is not dangerous as human cells produce and utilize it constantly to make proteins required for survival. The main concern is the encapsulation method used in delivering the mRNA to the cells. Moderna’s mRNA vaccine is encapsulated in a lipoprotein and current results from Phase 1 and Phase 2 trials shows limited side effect profile when used in healthy adults. A review published in Japan showed when encapsulated mRNA in nanoparticles were studied in mice, these nanoparticles crosses the placenta and can impede embryogenesis.
The heterogeneity that exists in encapsulation methods and materials (gold, silver, liposomes, et cetera) highlights the important need to thoroughly study compatibility in encapsulation mechanisms with gestation. Early animal studies can more definitively differentiate between safe encapsulation and higher-risk encapsulation methods for pregnancy.
The best-case scenario is that either 1) these lipoproteins do not cross the placenta at all, or 2) if the lipoproteins do cross, they are quickly ingested by fetal cells and the fetus are able to develop their own immune response.
What’s the verdict?
With so little known about mRNA vaccines even in healthy human trials, it is difficult to draw a definitive conclusion about its safety in pregnant women. The lack of sufficient data proving safety would make most clinicians wary of recommending it to pregnant women.
If Moderna’s mRNA-based vaccine will indeed be first-to-market in 2021, pregnant women will likely have to wait much longer before the data is clear on safety and rely instead on herd immunity to stay protected.