COVID-19 vaccines and Menstrual Cycles – What’s the Truth?
Female Body

COVID-19 vaccines and Menstrual Cycles – What’s the Truth?

Lamis Beshir Lamis Beshir

A regular menstrual cycle is considered a sign of good overall health. Our reproductive health and well-being are always a worry when our menstrual cycle begins or ends. Naturally, the length of a menstrual cycle may vary occasionally or from month to month, commonly during puberty, breastfeeding, or nearing menopause. However, if your cycle is getting shorter than 22 days or longer than 35 days, or you are experiencing irregular periods, this can be caused by many factors, including lifestyle, medications, and sometimes even vaccines.

The question of vaccines and irregular periods has been widely discussed on social media platforms for almost 1.5 years after the development of the COVID-19 vaccination.

Let's clear up your doubts and help you understand what an irregular period is? What causes irregular periods? How does the COVID-19 infection affect your menstruation and reproductive health? What effects do COVID-19 vaccines have on your period?

Irregular Periods (Irregular Menstrual Cycle)

Every woman is different, and so is their menstrual cycle.  In fact, you may have diversity in your own menstrual cycle. A predictable menstrual cycle length is roughly 22-35 days [1]. However, the usual length is mostly 28 days, and the cycle length is about 25-30 days [2]. So, what is considered an irregular period?

If you have an irregular menstrual cycle, you may have one or more of the following symptoms:

  • A change in the length of the menstrual cycle (the time between each period)
  • A noticeable difference in the number of days your bleeding lasts 
  • A higher than average blood loss during menstruation

 In medical terms, if your menstrual cycle is shorter than 20 days or longer than 45 days, it's usually called an irregular menstrual cyclhe [3]. It's normal for some women to have irregular periods, like teenage girls and older women who are going through menopause because of fluctuations in hormone levels. Research says that a teenage girl's menstrual cycle can be shorter, irregular, or longer in the first few years [4]. This irregularity is very common and usually caused by immature communication between the hypothalamus, the pituitary, and the ovarian glands that are not mature enough yet [5]. It is normal for older women to have irregular periods when they are in the perimenopause stage before actual menopause. Perimenopause is the time in a woman's reproductive life when her menstrual cycle changes and gets irregular until true menopause begins [6].

Causes Of Cycle Irregularity

Menstrual cycle irregularities are caused by a number of things, including lifestyle, hormonal imbalance, and some medical conditions. These include:

  • Eating disorders [7].
  • Thyroid problems [8].
  • Hyperprolactinemia [9].
  • Polycystic ovary syndrome [10, 11].
  • Certain medications: such as antidepressants and medications used for epilepsy treatment [12] [13].
  • Primary ovarian insufficiency [14].
  • Diabetes [15].
  • Stress [16].
  • Over exercise [17].

The Effects of Irregular Periods on Your Body

Irregular periods aren't always something to worry about. However, some irregularities, such as excessive or prolonged bleeding, can cause mild to severe iron deficiency or anaemia [18], which can lead to tiredness and weakness in some women.

Vaccines And Irregular Periods

The Internet is full of anecdotal reports from women reporting menstrual irregularities following COVID vaccines. This has led to a lot of misinformation and fear about the COVID-19 vaccine. Many women say they had heavy periods, as well as light bleeding, late periods, and more.

So, to clarify, we will discuss whether you get irregular periods after the COVID-19 vaccine or if it is just an assumption. Does the vaccine affect your fertility? Do COVID-19 vaccines affect periods, if at all?  Or can you take the COVID-19 vaccine during periods? While women worry about vaccine side effects, the COVID-19 infection has also been associated with some menstrual irregularities. Let's find out if COVID-19 directly affects the reproductive system & menstrual cycles or if other factors are involved.

What Does Research Say? Irregular Periods and COVID-19 Vaccines

The menstrual cycle is a complex system of hormones, tissues, and organs. It also responds to internal and environmental influences, including stress, infection, and lifestyle changes.  Vaccines induce an immune response and transient inflammation to protect the body from infection. During the COVID-19 pandemic, some women reported that it affected their menstrual cycles. Various investigations were conducted to gather data. Stress is possibly the main factor related to cycle disruption [19]. In times of stress, these changes are expected since the female body downregulates to allow recovery.

Evidence shows that females vaccinated against COVID-19 may experience menstrual irregularities, including longer menstruation and increased cycle length [20, 21]. A recent study on 2403 vaccinated women assessed the menstrual changes following vaccination. 55% of the vaccinated women received Pfizer-BioNTech, 35% Moderna, and 7% Johnson & Johnson/Janssen vaccines. The study reported that both vaccine doses only slightly changed cycle length (less than one day) compared to pre-vaccine menstrual cycles. It proved that vaccination is linked with only minor temporary changes in cycle length, but no clinically significant change occurs [20].

Until now, no study reported that the Pfizer or other COVID-19 vaccines stopped periods or affected females' fertility. If anything, only minor changes occur in the menstrual cycle after COVID-19 vaccines. But these are short-lived and the women experiencing these changes quickly revert back to their regular menstrual cycling. Therefore, we should encourage vaccination and contribute to the global efforts in controlling COVID-19. If you have any concerns, always discuss them with your gynaecologist or health care provider to make sure you receive evidence-based information. It is also important to discuss whether you have pre-existing gynaecological problems that could make you more vulnerable to menstrual irregularities so you can obtain accurate information about your situation.

The world health organisation encourages females to get vaccinated even if they are menstruating. Menstruation is not a contraindication to vaccination [22]. If you still have questions and worry about your menstrual health, you can speak to your health care provider.

Mechanisms Behind Irregular Periods after the COVID-19 Vaccine

Although there is still a lot to learn and unravel, studies are being done to look into this area more thoroughly and figure out what possible biological mechanisms might be at work. A few researchers have investigated some possible mechanisms. The immune system has been linked to periods changes either by having a direct effect on the hormones that control the menstrual cycle or by affecting the breakdown and build-up of the uterine lining (endometrium) [23]. Scientists think that these underlying mechanisms may be similar to menstrual changes in the natural COVID-19 infection. People who have a natural infection may also have a lower menstrual volume or longer cycle due to transient ovarian dysfunction [24]. 

Another theory claims that the similarity between the SARS-CoV-2 spike protein and syncytin-1 [25], a protein that is important for the formation of the embryo, may make the body react in some way. The theory suggests that the immune system will think the syncytin-1 protein isn't from the body and react to it, which will stop embryo implantation. However, no one has been able to back up this claim with any scientific evidence [26]. 

Much of the public concern around this issue arises from misinformation that vaccine-associated menstrual irregularities cause female infertility [27]. We know that this is not the case. Despite reported irregularities, females were able to conceive both naturally and using assisted reproduction. Women who were already attending fertility clinics before vaccination did not seem to experience alterations in their fertility, ovarian reserve, IVF cycle outcomes, fertilisation rate, and the number and quality of embryos [28].

COVID-19 Infection is Also Associated With Menstrual Irregularities 

A study conducted at the University of Arizona consisting of 127 COVID-19-infected women found that 16% of women had altered menstruation cycles. Those who reported menstrual cycle alterations had higher COVID-19 symptoms and comorbid illnesses. 35% had longer menstrual cycles, 60% had irregular periods, and 45% experienced worsened premenstrual symptoms (PMS) [29]. 

A few studies have also examined in-depth the biological aspects of a COVID-19 infection in the uterus, and the receptors used by the virus to enter the cells and cause disease. The uterine lining (endometrium) was examined for the virus’ nucleic acids, ACE2 receptor, TMPRSS4 gene, and other related genes. There is good news for us: the expression of these genes is low in the uterus, protecting the endometrium from any local COVID-19 infection, and the virus has hardly been isolated [30, 31].

These studies reflect that the SARS-CoV-2 infection may mildly affect the menstrual cycle, accompanied by other factors such as stress and immune response, but these changes are minor and reversible.

Stopping the Misinformation and Fear

Vaccines have been proven to protect from COVID-19 severe disease and hospitalisation while building herd immunity. Their side effects are short-lived and are much less severe than those of the COVID-19 infection. To date, the evidence we have is reassuring. Further studies and additional reporting of these menstrual irregularities following vaccination will allow the scientific community to provide us with a better understanding of the effects of both infection and vaccination on the menstrual cycle and fertility. Relying on information provided only by scientists and the healthcare community ensures that we stop misinformation that is causing concern among women.



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