Below, doctors and epidemiologists answer five common questions regarding the safety of the COVID vaccine for pregnant women.
1. Have the vaccines been tested on pregnant women?
In June, the Centers for Disease Control and Prevention (CDC) published an interim analysis of long-term outcomes in pregnant women who received the vaccine. They found no increase in adverse pregnancy outcomes compared to the rates normally reported in the general pregnant population, before the pandemic.
That said, none of the vaccines to date—and this includes the Pfizer, Moderna, and Johnson & Johnson vaccines—have been formally tested on pregnant women. "None of the trials included women who were actively trying to conceive or already pregnant/breastfeeding," says Lucky Sekhon, MD, fertility specialist and board-certified OB/GYN. "[Excluding pregnant/breastfeeding women] is standard practice for any clinical trial studying a new therapy [or] drug." (This is typically because researchers don't know how a drug could potentially impact the health or development of a fetus.)
Instead, researchers often rely on animal studies for safety guidance. Dr. Sekhon notes that the Moderna vaccine was tested on rats who were mated, and no difference was found in their ability to get pregnant, in fetal development, or in the health of their offspring when compared to rats who did not get the vaccine. Animal testing using the Pfizer vaccine also did not indicate harmful effects concerning pregnancy, fetal development, or post-natal development.
Also worth noting: Around two dozen women inadvertently conceived during the Pfizer vaccine trial, and Dr. Sekhon says. A significant number of pregnant women have also opted to get the vaccine since it's become available in the U.S. "So far, there are no red flags or concerning data coming out of the 10,000 pregnant women who have received the vaccine thus far," says Dr. Sekhon. All in all, fairly promising (although not totally conclusive) signs of the safety of these vaccines for pregnant women.
2. What are the potential risks of getting the vaccine for pregnant people?
Generally, vaccines themselves are typically fairly safe for pregnant people; women have been and continue to be safely vaccinated during pregnancy for other illnesses, including tetanus, diphtheria, and whooping cough. "We have history of other vaccines in pregnancy that are given safely, so we're looking at that as sort of kind of reassurance, if you will, to say we are used to vaccinating pregnant women, as opposed to doing some completely novel treatment that nobody's ever tried before," says Laila Al-Marayati, MD, division chief of obstetrics and gynecology, Keck Medicine of USC.
Pregnant people are even counseled to get flu shots; however, the ones they receive specifically do not contain live viruses because pregnant women are advised against receiving vaccines that do (e.g., the measles, mumps, and rubella vaccine) due to the theoretical risks of passing that virus to the fetus.
Fortunately, the vaccines currently available to prevent COVID-19 do not contain live virus. The Pfizer and Moderna vaccines use messenger RNA (mRNA) technology, which basically provides our cells with instructions to build a protein found in the SARS-CoV-2 virus so that the immune system can create the antibodies needed to protect against COVID-19 infections. This mRNA degrades, or disappears, quickly once the protein is developed, leaving the cells as they were. "Since neither vaccine contains live virus and mRNA does not integrate into the human DNA genome, there is no theoretical reason to assume there is a risk to pregnant women or their fetuses," says Timothy Brewer, MD, professor of medicine and epidemiology at UCLA.
3. Since some vaccines utilize different technologies, is one type of vaccine potentially safer than another?
New vaccines utilizing different, non-mRNA technologies are forthcoming. Johnson & Johnson, for example, sends the genetic code for the SARS-CoV-2 protein into cells by injecting the body with an adenovirus (a common virus, such as that which causes a cold) that's been modified so that it can enter cells but not alter them or replicate. While this vaccine has not been tested on pregnant women either, other vaccines using the same adenovirus technology have been given to women who got pregnant during those trials. Johnson & Johnson has reportedly said there is no concerning evidence of ill effects as a result, so theoretically, the risks would be similar with this new COVID-19 vaccine, too. The AstraZeneca and Novavax vaccines (not yet approved for use in the U.S.) also utilize a weakened adenovirus that's been modified to look like SARS-CoV-2.
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As for whether or not adenovirus versions of the vaccine are potentially safer for pregnant women than the Moderna or Pfizer vaccines, or vice versa, Dr. Sekhons says there's no safety difference between the two. "All of the major vaccines use either mRNA or inactivated virus delivered by the common cold virus or an inactivated protein subunit of the COVID-19 virus," she says. "None of the vaccines are live virus vaccines, which are contraindicated in pregnancy and considered a danger."
4. How are expert organizations and OB/GYNs advising pregnant women regarding the vaccine at present?
There is professional consensus around the idea that pregnant people should get the vaccine. The American College of Obstetricians and Gynecologists (ACOG), the Centers for Disease Control and Prevention (CDC), the World Health Organization (WHO), and the Society for Maternal-Fetal Medicine (SMFM) strongly recommend that pregnant people get COVID-19 vaccines.
From there, experts say it's important to note that pregnant people are at increased risk for COVID-19. "I advise [patients] to weigh their personal risks of COVID-19—increased risk of severe disease, hospitalization, need for mechanical ventilation, and death as a pregnant woman who catches COVID-19, and the increased risk of preterm delivery prior to 37 weeks—which may also include their risk/threat level...against the risks of the unknown," says Dr. Sekhon. "My personal viewpoint, having reviewed the data at hand and the indirect evidence versus what we know about COVID-19 in pregnancy, is that all pregnant women should strongly consider taking the vaccine."
"My personal viewpoint, having reviewed the data at hand and the indirect evidence versus what we know about COVID-19 in pregnancy, is that all pregnant women should strongly consider taking the vaccine." —Lucky Sekhon, MD, OB/GYN
Dr. Al-Marayati is in the same boat. "Our position, at least in my practice, is that we believe any potential risks are outweighed by the benefits of not getting COVID. So we recommend vaccines for pregnant patients." But COVID-19 can be dangerous, period, she adds. Research shows that pregnant women with symptomatic COVID-19 are more likely to experience intensive care unit admission, invasive ventilation, and death than non-pregnant women with symptomatic COVID-19. Even if an infection is not that bad, she'd prefer that her patients avoid it because pregnancy can complicate treatment and vice versa.
The ACOG does recommend that women treat any fevers that may arise from the vaccine, says Dr. Sekhon, and that they refrain from taking any other vaccines for at least 14 days, with one exception: the RhoGAM shot (which protects you and your fetus from complications arising from blood type incompatibility).
5. If you're planning a pregnancy this year, is it best to get a vaccine first? And can the vaccines affect fertility?
While you should get vaccinated as soon as you're eligible, according to Dr. Sekhon, there is no evidence to suggest that it's better to get vaccinated before pregnancy than during. "I would not factor this into planning," she says. And despite rumors to the contrary, there is no evidence or reason to believe that COVID-19 vaccines will affect your fertility if you do wait until after vaccination to attempt conception. "The vaccine cannot impact your fertility or ability to conceive," says Dr. Sekhon.
She says that the specific theory around infertility and the vaccine—which is that the proteins created/injected by COVID-19 vaccines are similar to those found in a healthy placenta, and therefore developing antibodies to attack them could cause fertility issues—has been debunked. "The theorized cross-reactivity between the antibodies directed against the coronavirus spike protein and the placental protein, syncytin-1, has been disproven," she says. "We also see similar levels of similarity in the genetic sequence of the spike protein and proteins that make up collagen and hemoglobin, which are ubiquitous in our bodies. Clearly, there is no cross-reactivity between the antibodies from the vaccine and these proteins, given the favorable side effect profile and safety demonstrated in large trials." In other words, if the vaccine were causing attacks on proteins in the body similar to the COVID-19 proteins it creates/injects, we would already have data, unrelated to pregnancy, showing that to be the case.
This conclusion is fairly definitive. And, as you weigh your options, it's best to work with your health-care providers to make a decision considering the above information alongside your own health data and exposure risk.
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