Women have been more likely than men to report adverse reactions to COVID-19 vaccines — and public-health experts say preparing them for the range of possible side effects could help combat vaccine hesitancy.
Women accounted for about 79% of adverse-event reports — most of them deemed “nonserious” — related to Pfizer PFE, +2.58% -BioNTech BNTX, +7.69% and Moderna MRNA, +6.84% coronavirus vaccine doses administered in the U.S. from Dec. 14 to Jan. 13, despite receiving only 61% of administered doses, according to a Centers for Disease Control and Prevention report.
Anaphylaxis, a rare but potentially life-threatening allergic reaction, has also occurred overwhelmingly in women who received the two mRNA vaccines.
U.S. health officials last week also announced a pause in administering the Johnson & Johnson JNJ, +1.15% vaccine to examine reports of ultra-rare blood clots that appear to disproportionately affect women. The clotting issue is similar to one observed with the AstraZeneca AZN, -0.18% vaccine — also seen primarily in women — in the European Union and U.K.
The six blood-clot cases initially identified in the U.S. occurred in women ages 18 to 48; one woman died, and another was in critical condition. The list of cases later grew to include a seventh woman and one man, the New York Times reported.
Meanwhile, reports of post-vaccination lymph node swelling have spurred concern over potential false positives in breast-cancer screenings. And researchers, based on emerging anecdotal reports, are gathering survey data from people who say they experienced unusual short-term changes in their menstrual cycle after getting vaccinated.
“ The majority of side effects that people experience from the vaccines are minor. ”
“The more we talk about it, the more we’re validating the symptoms that people are having [and] demonstrating that we’re responsive,” said Aparna Kumar, a psychiatric mental-health nurse practitioner, assistant professor at Thomas Jefferson University, and chief community officer at Dear Pandemic, a science-communication project. “And, of course, we’re taking action with the J&J vaccine.”
The majority of side effects that people experience from the vaccines are minor, added Rosemary Morgan, a research scientist at the Johns Hopkins Bloomberg School of Public Health — “and if you do experience a side effect, it means your immune system is working.” (Your immune system is still working even if you don’t have side effects, she added.)
Here’s what we know — and still don’t know — about COVID-19 vaccine side effects in women:
Multiple factors could explain sex and gender differences
Morgan said she believes sex and gender differences in reported COVID-19 vaccine side effects are the interaction of biological differences, behavioral differences, and historical and still-ongoing gender bias in clinical research.
For starters, Morgan and other experts weren’t surprised that women seemed to be experiencing more adverse reactions to coronavirus vaccines. “When we look at studies on other vaccines and adverse reactions, we are seeing quite a big gender difference,” she said. (Some of this relates to how estrogen and testosterone impact the body’s immune response.)
“Women have an overall greater immune response,” she said. They are also, on the flip side, more likely to have autoimmune disorders.
“ ‘Many drugs on the market today are based on dosages that were measured against the male body and then stated to be effective for everybody.’ ”
Based on research suggesting men are less likely to seek help from healthcare providers, Morgan said, it’s also possible that women are more likely to report adverse vaccine reactions regardless of whether they’re experiencing more adverse reactions than men. Men have issues “thinking about masculine norms of what it means to be healthy and not showing weakness,” she said.
The fact that clinical research trials largely excluded women prior to 1993 — along with bias that persists because researchers often don’t disaggregate data on adverse reactions by sex — may be a third factor, Morgan added. (Clinical trials for coronavirus vaccines did, of course, include women.)
“Many drugs on the market today are based on dosages that were measured against the male body and then stated to be effective for everybody,” Morgan said. “Because we’ve got these standard doses of medications and vaccines, are women receiving more than they need for it to be effective?”
You may want to reschedule your upcoming mammogram
Some patients who received COVID-19 vaccines have reported temporary lymph-node swelling in their underarm. This type of inflammation signals a healthy immune response, but could trigger a false positive on a mammogram, said Jennifer Lighter, a hospital epidemiologist at NYU Langone Health.
“That replication of the immune cells that’s occurring in the lymph node — that’s causing a little bit of swelling,” Lighter said. “And a little bit of swelling is something to pick up on a mammogram, because breast cancer can cause inflammation or swelling of the lymph nodes.”
Assuming you’re receiving a two-dose vaccine, the Society of Breast Imaging recommends that you consider scheduling your screening exam either before your first vaccine dose or four to six weeks after the second dose.
Only consider putting off a mammogram if the postponement won’t “unduly delay care,” the American College of Obstetricians and Gynecologists (ACOG) adds. And if you do receive a mammogram less than four to six weeks after your shot, tell the radiologist or technologist which vaccine you received, when you got it, and in which arm to help the provider interpret your results.
The vaccines are unlikely to pose risks for pregnancy or fertility
While trials for the currently authorized COVID-19 vaccines did not include pregnant individuals, experts believe the vaccines are “unlikely to pose a specific risk for people who are pregnant,” the CDC says.
The vaccine makers are monitoring data from people who received the vaccines in trials and became pregnant, and studies to examine the vaccines’ safety and efficacy in pregnant people are “underway and planned.” Pregnant people are, however, at greater risk for severe COVID-19 illness.
There’s currently no evidence that “any vaccines, including COVID-19 vaccines,” cause problems with fertility, the CDC adds.
“While fertility was not specifically studied in the clinical trials of the vaccine, no loss of fertility has been reported among trial participants or among the millions who have received the vaccines since their authorization, and no signs of infertility appeared in animal studies,” ACOG said in a joint statement with the American Society for Reproductive Medicine (ASRM) and the Society for Maternal-Fetal Medicine.
As for individuals scheduled for reproductive-care treatments such as egg retrieval, embryo transfer and intrauterine insemination, ASRM recommends avoiding coronavirus vaccination for at least three days before and three days after the procedure.
This is not because vaccination is unsafe, but because the vaccine’s known side effects — which include fever, chills, headaches and fatigue — “may impact intra-operative and post-surgical monitoring,” the organization said. ASRM has more information on fertility treatments and COVID-19 here.
“If one initiates the treatments, then has a COVID-19 vaccine, they should follow appropriate guidance for that vaccine (for example, if someone has Moderna, they should still get the second dose at four weeks, even if undergoing treatment),” Kumar added. “The general idea is that additional factors should be decreased during treatments, so if able to delay, one might delay or defer fertility treatments until after the vaccine.”
The recommended waiting time after getting vaccinated varies depending on the provider or practice, she said, but is generally a minimum of two weeks, and preferably four to six weeks.
Serious blood clots after vaccination are extremely rare
Federal health officials have stressed that cerebral venous sinus thrombosis (CVST), the type of blood clot seen in combination with low blood-platelet levels in the six U.S. women who received the J&J vaccine, is “extremely rare” and has only occurred in less than one in a million vaccinated individuals.
By the time U.S. officials recommended the “pause,” about 6.8 million people in the country had received that vaccine. A CDC advisory committee voted Wednesday to extend the pause, and is slated to meet again on April 23.
In all six cases, symptoms developed between six and 13 days after vaccination, the CDC and Food and Drug Administration said. J&J vaccine recipients who begin experiencing severe headache, abdominal or leg pain, or shortness of breath within three weeks after getting vaccinated should reach out to their healthcare provider.
For more on next steps if you received the J&J shot, and the future of the one-dose adenovirus viral vector-based vaccine, check out MarketWatch’s guide here.
There are anecdotal reports of menstrual-cycle changes
Katharine Lee, a biological anthropologist and postdoctoral research scholar at Washington University School of Medicine in St. Louis, and Kathryn Clancy, a University of Illinois associate professor of anthropology who was Lee’s dissertation advisor, launched an online survey earlier this month after they both experienced post-vaccine menstrual irregularities — and heard several other menstruators, including on Twitter, share their own experiences.
As of midday Friday, about 24,600 people had initiated the survey, Lee said.
“A lot of people report that they found out about this project because they experienced something weird and Googled GOOG, +0.05% ‘period’ and ‘vaccine,’” Lee told MarketWatch. “We felt like it was necessary and useful to allow people to report those experiences, in order for us to look at the data and think through what some possible mechanisms and next questions might be.”
Individuals report a wide range of experiences, Lee said: Many don’t notice any change, while others have reported much heavier menstrual bleeding, lighter periods, or differences in timing or duration.
Some people who don’t typically experience a period, including long-acting reversible contraception users and transgender men undergoing gender-affirming medical care, have said they were surprised to experience spotting or a period for the first time in a while, she added. Perimenopausal and postmenopausal people have also reported bleeding or having menstrual cycles.
Lee and Clancy have hypothesized this may only be a short-term change. Lee also emphasized that she remains in favor of vaccinations.
Research on vaccines and the menstrual cycle is scant, though a recent inquiry by OB-GYN and pain-medicine physician Jen Gunter turned up a retrospective Japanese study in which researchers asked HPV vaccine recipients about their post-vaccination symptoms, including menstrual bleeding.
“ A variety of lifestyle factors and medical conditions can cause menstrual irregularities. ”
There are still many unknowns surrounding the current anecdotal reports, Kumar noted, including the nature of the symptoms, whether there is any relationship between the vaccine and menstrual side effects, and what the potential mechanisms could be. (Gunter’s Substack post includes some theories.) A variety of lifestyle factors and medical conditions can cause menstrual irregularities.
“We want to know how many people, who, which symptoms specifically, onset, etc. The anecdotal reports won’t tell us specific numbers. And anecdotes can be just coincidence unless we have such specifics,” Kumar said. “How frequent is this side effect? Is it on the level of something else expected, in terms of percentages or number of people who report out of all who get vaccinated?”
But Kumar, who in her capacity as a nurse has also heard reports of menstrual irregularities after vaccination from at least 20 people, added that she was “excited that people are trying to gather more data.”
“Side effects are happening,” she said, “so it’s important that we identify them and educate people on them so they can be well-informed and know that it’s normal.”