Update on mRNA Vaccines: Slight Menstrual Disruptions Still Do Not Translate to Fertility Problems

They’re at it again. Anti-vaccine activists once again are spreading misinformation aimed to promote fear of mRNA vaccines among women of reproductive age. A quintessential example is recent tweet, posted February 2, 2023, by Rep. Marjorie Taylor Greene, who claims not to have been vaccinated against SARS-CoV2 (the virus that causes COVID-19). Right after saying that “many women have reported problems with their menstrual cycles after taking vaccines”, without elaborating on the “problems”, she refers to miscarriages, without noting that miscarriages are very common. This leads to the implication that the vaccines are the cause of the miscarriages. Then, by stating that “we need answers”, she implies that reproductive issues have been ignored in the context of vaccination, when researchers have been studying this with government funding. All this is part of a tweet in which she retweets a tweet from the far right-wing political group, Project Veritas, that included a casual interview with a Pfizer researcher, noting that vaccines have side effects and alluding to how mRNA technology is poised to move far beyond vaccination to things such as cancer therapy.

This means that it’s time for us to have a refresher discussion about mRNA vaccines and reproductive health, a discussion in which we can dive into the menstrual issues and add some context to the Pfizer researcher’s bar room comments with respect to mRNA therapies. In referring to the mRNA vaccines, we mean the vaccines of Pfizer-BioNTech and Moderna.

To begin, we should note that it’s 100 percent true that women have noted changes in their menstrual cycles after receiving a vaccine against SARS-CoV2. This happens during the first month after a vaccine dose and it does not seem to be something particular to the SARS-CoV2 vaccines. Your body reacts to vaccine doses, whether tetanus boosters, flu shots, or vaccines to prevent COVID-19. It’s common to get some soreness, headaches, chills, or mild fever, and this, in turn, can affect the timing of menstruation. Your immune system, after all, is boosting levels of various chemicals called cytokines, which control various immune cell, but also influence other aspects of your physiology. But it is a very big stretch on the part of Rep. Greene to refer to the reported menstrual cycle changes as “problems”.

What Rep. Greene did in that tweet was merely a repeat of what Dr. Robert Malone did in his notorious 3 hour interview with Joe Rogan in late 2021, leading us to debunk him here on The Pulse one year ago. Related to this, in a different post, we also took a deep dive to debunk a claim that COVID-19 vaccines affected the placenta and fertility on account of similarities between the coronavirus spike protein and a protein important to fertilization and also to holding the placenta to the endometrium of the uterus. What actual studies have shown is that vaccine doses can change the timing of menstrual cycles by small amounts of time with no implications on fertility.

Several months prior to the Rogan-Malone interview, the National Institutes of Health (NIH) had announced the availability of millions of dollars in government grant money to study the issue and various clinical research centers took the NIH up on the offer. One study based at Oregon Health Sciences University, for instance, which later published in the Journal Obstetrics and Gynecology, examined information on the timing and characteristics of menstruation, on vaccine doses, and on other factors from nearly 4,000 women reporting through a phone tracking app. The study found that getting a vaccine jab can affect the length of your menstrual cycles, but only by a matter of hours, or up to a day out of the entire month. For women who received two vaccine doses during the same cycle, the timing of their periods could change by up to two days. Some women experienced some heavier than normal bleeding, but the amount of bleeding and the lengths of cycles, went back to normal within two cycles. Maybe you would call this a problem and maybe not, but what about the question of fertility?

On that question, the Boston University School of Public Health released a study, also funded by the government, on effects of COVID-19 vaccine jabs, SARS-CoV2 infection, and COVID-19. This involved more than 2,000 Canadian and US couples trying to conceive. The researchers found that vaccination did not interfere with fertility. However, infection with SARS-CoV2 (the virus that causes COVID-19) was shown to cause a temporary drop in fertility in males who were infected. This means that if you and your male partner want to be fertile as a couple, the man should be vaccinated for that purpose, although you both should be vaccinated for the sake of your own health, and the health of your future baby.

As for what the Pfizer researcher meant in relation to applications of mRNA outside of vaccination, this is not something that should scare you. It is actually part of a very exciting trend to apply the same delivery system that gets you immunized against SARS-CoV2 to do something else, like transform certain of your immune cells to kill off particular cancer cells, or to remove fibrous tissue that is damaging the heart. For these more ambitious applications of mRNA, the clinical setting is a deadly disease that has already emerged in the patient and we’re talking about sending in mRNA instructions to transform cells such as killer T lymphocytes into guided missiles. This technology is advancing, and it is expected that it will reduce damage to healthy tissues dramatically compared with current treatments.

As for the vaccine applications anti-vaccine activists have spread much fear about the spike protein. The mRNA carries instructions for cells of the vaccine recipient to manufacture small quantities of a portion of this protein. The most important cells to do this are called antigen presenting cells. In the germinal centers of the lymph nodes in the axilla on the side of the body where the vaccine is injected, antigen presenting cells cause an immune response. Various other types of cells also receive the instructions, but all the cells that end up making spike protein display the protein on the outside of their membranes. This leads to immune responses that ultimately destroy those cells. Consequently, other than the immunization, there are no permanent changes. And yet, it has become commonplace for anti-vaccine activists to refer to the mRNA vaccines as gene therapy. Whether or not it would be bad if it were gene therapy, it’s important to note that, in gene therapy, the point is to modify the genetics of cells that are going to stick around for a long time. If you have a deficiency of an enzyme that the liver is supposed to synthesize, for instance, the goal of gene therapy is to get genetic material into liver cells that will persist and behave differently on account of that genetic modification. You cannot achieve this with mRNA, because it has an extremely short half-life, meaning that it degrades very quickly. You must use DNA, which is much more stable and, even with DNA, it has to function inside cells that are not destroyed on account of what the DNA is causing the cell to make.

David Warmflash
Dr. David Warmflash is a science communicator and physician with a research background in astrobiology and space medicine. He has completed research fellowships at NASA Johnson Space Center, the University of Pennsylvania, and Brandeis University. Since 2002, he has been collaborating with The Planetary Society on experiments helping us to understand the effects of deep space radiation on life forms, and since 2011 has worked nearly full time in medical writing and science journalism. His focus area includes the emergence of new biotechnologies and their impact on biomedicine, public health, and society.

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