As COVID-19 vaccines continue to be rolled out across Australia, it makes sense that people will want to share their experiences of vaccination and get a better understanding of possible side effects. Some of those discussions focus on whether vaccines could have any impact on reproductive health: can vaccines affect fertility or pregnancy? Could a vaccinated person have an impact on others around them? And what’s going on with all the stories of people noticing changes in their menstrual cycle?
We all want to make the best possible decisions for our health and the health of others—and especially if there’s a new baby on the way. Let’s dive into some of the discussions happening around COVID-19 vaccines, fertility and menstruation to sift through the claims and the evidence.
What is ‘shedding’?
The term ‘shedding’ has come up in some conversations around whether a vaccinated person can affect other people around them—and no, it’s got nothing to do with spending time in small backyard structures or fluffy pets getting ready for summertime.
No, not that kind of shedding. Image adapted from: Jinen Shah/Unsplash; CC0
Viral shedding occurs when someone infected with a virus starts to release viral particles from their body into the surrounding environment. This enables the virus to spread and be transmitted from one host to another and is a normal, expected process once someone is infected.
For vaccines, it’s a different story: most vaccines cannot result in shedding of any kind of infectious particles at all.
The only vaccines with any potential to shed infectious particles from one person to another are live virus vaccines, which are made using a living virus that has been weakened (or attenuated) in a laboratory. The viruses in vaccines like these have been permanently altered so they can still reproduce and stimulate an immune response, but they don’t cause disease. Examples of live virus vaccines used in Australia include the chickenpox and rotavirus vaccines. Even if a vaccinated person sheds some viral particles, it’s extremely rare to spread enough of the virus, and for it to be strong enough, to cause disease in another person.
By protecting yourself with vaccination, you can help protect others from COVID-19.
None of the COVID-19 vaccines are live virus vaccines: there is no way they could spread the SARS-CoV-2 virus. Instead, they prompt the body to create a spike protein—the part of the virus that attaches to a host cell—which is not infectious by itself and cannot be shed out of the body. Once built, these spike proteins will linger in the body just long enough for the immune system to develop antibodies against them. The spike proteins, and the genetic instructions your cells use to build them, break down naturally.
Can COVID-19 vaccines affect fertility?
Researchers developing vaccines take a cautious approach towards pregnant people while vaccines go through clinical trials. It’s normal for guidelines for trial participants to specify that they should take steps to avoid pregnancy during the trial, and if someone does fall pregnant, they should take extra precautions and notify researchers so that they can be monitored more closely. This is a standard measure that gets put in place until clinical trials are complete to ensure vaccine safety.
Recent studies have shown there is no evidence that mRNA-based COVID-19 vaccines (such as the Pfizer vaccine) have an impact on pregnancy or fertility. A study of over 35,000 pregnant people in the US who received an mRNA vaccine showed that side effects after vaccination are similar to those experienced by non-pregnant people. The chances of serious events like miscarriage or placental abnormalities are similar for both vaccinated and unvaccinated people. This is not surprising, as there is no reason to suspect that any of the COVID-19 vaccines should have a negative effect on fertility or pregnancy outcomes. Studies have also demonstrated that the mRNA COVID-19 vaccines are really effective at reducing COVID-19 harm in pregnan cy .
Large studies on other vaccines have consistently reported no impact on fertility . In fact, there is strong evidence that vaccination in pregnancy protects against infection, and may even reduce incidence of stillbirth . Additionally, studies on both humans and animals on the Pfizer and Moderna COVID-19 vaccines have not s hown any negative impacts on fertility or pregnancy.
People trying to become pregnant do not need to delay vaccination for COVID-19 or avoid becoming pregnant after vaccination. Image adapted from: Mart Productions/Unsplash, CC0
What about COVID-19 itself? Research into pregnant and recently pregnant women who become sick with COVID-19 shows that there is a higher risk that both the mother and their newborn could be admitted to an intensive care unit in hospital or needing life support ventilation when compared to women who have not had COVID-19. There is also a higher risk of delivering a baby prematurely. Pregnant people with other risk factors , including being overweight or more than 35 years old, or having pre-existing high blood pressure or diabetes, are also at higher risk of severe illness from COVID-19 compared to pregnant people without these conditions.
Because of the increased risks from COVID-19 during pregnancy, it is recommended that pregnant people in Australia receive the Pfizer (Comirnaty) vaccine or Moderna (Spikevax) vaccine at any stage before, during or after their pregnancy, including while breastfeeding. Some small studies have suggested that COVID-19 vaccination may also provide indirect protection to babies by transferring antibodies through the placenta or through breastmilk, although research in this area is still ongoing.
There has also been a claim that the SARS-CoV-2 spike protein has a similar structure to a protein found in the human body called syncytin-1, which plays an important role in forming the placenta during pregnancy. Some people have thought that if the immune system develops antibodies against the spike protein, those antibodies might also mistakenly attack syncytin-1 based on its supposedly similar shape, therefore harming a pregnancy. However, syncytin-1 and the SARS-CoV-2 spike protein have very different structures, so the underlying idea does not hold true .
Do COVID-19 vaccines change your menstrual cycle?
Some people have said they noticed changes in their menstrual cycle after receiving a COVID-19 vaccine: some say their period was heavier or lighter than usual, or it arrived earlier or later than expected, for example. The number of people noticing changes has raised a few questions, such as: are these kinds of menstrual changes normal after a vaccine?
Menstrual cycles can be affected by a range of different factors, such as age, medication, illness, sudden diet or exercise changes—and stress. Evidence shows that the stress of the COVID-19 pandemic itself has had an impact on people who experience menstrual disorder , with some study participants saying their symptoms are worse, the duration of their period has changed, and their anxiety levels have risen. It’s possible that pandemic-induced stress may be contributing to the changes people have noticed in their periods following vaccination, rather than being attributable to the vaccine itself. Some people may find vaccination to be a stressful event that adds to the range of factors impacting their menstrual cycle.
Some people have reported changes to their menstrual cycles following a COVID-19 vaccine. Image adapted from: Sora Shimazaki/Unsplash; CC0
It’s also important not to confuse temporary menstrual changes with long-term fertility. While there is a possibility that COVID-19 vaccination might temporarily change the timing of bleeding or ovulation, this would not have impacts on the future ability to conceive or have children.
As for whether your vaccination can affect people around you? There is no scientific evidence that simply being around a vaccinated person is going to affect another person’s period. By protecting yourself with vaccination, you can help protect others from COVID-19, a disease with potentially serious consequences—that’s the biggest impact your vaccination can have on other people. Your decision to get vaccinated matters.
This article is based on scientific evidence but is not medical advice. Please speak with your doctor for advice regarding your personal circumstances and vaccines for COVID-19.
Funded by the Australian Government Department of Health.
This article was produced by the Australian Academy of Science and has been reviewed by the following experts: Professor Sarah Robertson FAA FAHMS Professor, Adelaide Medical School; Professor Lois Salamonsen FAA, Head: Endometrial Remodelling Laboratory, Hudson Institute of Medical Research, Professor Beverley Vollenhoven AM, Director of Gynaecology, Monash Health. The writing of this article was supported by Academy staff: Emma Berthold and Dr Hayley Teasdale. . Published 22 July 2021. Updated 25 January 2022.
