What the science says about fertility and COVID vaccines

• "Women of childbearing age should absolutely be vaccinated," says CDC medical officer Christine Olson, who is head of the v-safe pregnancy registry.

Threat level: Pregnant people who have a symptomatic COVID infection "have a twofold risk of admission into intensive care and a 70% increased risk of maternal death," particularly with the highly transmissible Delta variant, Olson says.

• There is also a higher risk of adverse pregnancy outcomes including preterm birth, stillbirth and admission into the ICU of a newborn also infected with COVID-19, she adds.
• The CDC tracker of pregnant people from Jan. 22, 2020, to Oct. 4, 2021, shows there've been 127,193 known cases, with 22,329 hospitalizations and 171 deaths.

What's happening: There are "thousands and thousands and thousands" who are reporting an impact from the COVID vaccine, particularly on menstruation, says Namandjé N. Bumpus, director of the department of pharmacology and molecular sciences at Johns Hopkins University School of Medicine.

• However, Bumpus adds, "it remains to be seen if there's a causal link or not."
• Olson points out that the CDC "is aware of reports of menstrual irregularities" and continues studying the issue. NIH is funding five one-year supplementary grants worth $1.67 million to further investigate if there's a link and what the underlying mechanisms may be.
• One of the theories is that the change in a person's period could be caused by a temporary immune response to the vaccine, as the endometrium lining the uterus contains multiple immune cells, says Alice Lu-Culligan, an M.D.-Ph.D. student at Yale School of Medicine who is researching the topic and wrote an opinion piece in April.

Changes in menstrual cycles can be caused by many factors like stress or new medications, can happen frequently, and often are temporary without an impact on fertility, says Viki Male, a lecturer in reproductive immunology at Imperial College London.

• The problem, she says, is the combination of the infertility misinformation with people saying, "Oh, I noticed it changed my period." This has led to hesitation and questions like: "You say they don't cause infertility but if they don't cause infertility, then why has my friend's period come five days late?"
• "But people find [menstruation] goes back to normal very quickly," Male says.

• "Alteration of someone's period does not mean they were infertile that month," Lu-Culligan adds.

Background: Misinformation about the vaccine's effect on fertility was first promulgated in the U.K. in December by Michael Yeadon, a former Pfizer vice president, Male says. Since then, many different scientists have looked closely at the allegation, she says, and found no evidence to support that claim.

• "The concern about infertility is hypothetical. There is no current evidence to support this, and there are most certainly pregnancies occurring every day following COVID-19 vaccination," Olson says.

Between the lines: Multiple sources say the decision in the early clinical vaccine trials to exclude pregnant people fueled hesitancy.

• "It was a dreadful mistake to not include people who are pregnant in clinical trials" for COVID-19 vaccines at first, Male says. "We should have known that we were going to need to vaccinate people who are pregnant, but we ended up without trial data from them. I think that's something we should also learn from in the future."
• "A lot of that early opportunity was lost" by not including pregnant people in the vaccine randomized control trials with a blinded placebo cohort, Lu-Culligan says. "There are trials going on right now, but we have to wait for those and wait for the numbers to accumulate."

The bottom line: Vaccination is essential "for anyone wanting to make sure their pregnancy is the healthiest it can be and results in a healthy infant," Olson says.