TORONTO -- You may have heard the warning from a friend or a relative: “Don’t give your daughter the COVID-19 vaccine if you want grandchildren.”

Concerns about whether these vaccines will cause long-term fertility-related issues have rekindled as more children aged 12 and over are vaccinated in Canada and elsewhere, but experts say studies, along with time-tested scientific research around vaccines, show these claims are baseless.

In Canada, the Pfizer-BioNTech vaccine was authorized in May for 12 to 15 year olds and Health Canada is currently reviewing Moderna’s application for those aged 12 to 17. Already, close to three million U.S. children between 12 and 17 have been vaccinated and clinical studies show the vaccines are safe and effective for that age group, says, an information portal for parents, caregivers, youth and health providers created by the Children’s COVID-19 Vaccine Advisory Table.

The Ontario-based group is made up of more than two dozen infectious disease, pediatric, and public health experts, among others, representing more than half a dozen eminent children’s health organizations including SickKids, the Children’s Hospital of Eastern Ontario, and McMaster Children’s Hospital. The Canadian Paediatric Society also advocates for the COVID-19 vaccination of all children and adolescents aged 12 years and over.


The myth around infertility started when someone thought the spike protein created by the mRNA vaccine was similar to a protein found on the placenta called syncytin-1, said molecular and cellular biologist Dr. Krishana Sankar with COVID-19 Resources Canada.

The concerns were raised by a German physician and soon spread on social media.

“Basically, they were trying to say that because there were similarities … with syncytin-1, then we would create antibodies against syncytin-1, which means it would affect our fertility,” said Sankar, who is also the scientific liaison for an anti-misinformation campaign, ScienceUpFirst.

“That’s actually not true. For that to be true, syncytin-1 would need to be extremely, extremely similar to the spike proteins that we create for antibodies -- and it is not. The amount of similarity is very miniscule. So any antibodies that we generate in our bodies to the spike protein would not actually affect the protein on the placenta called syncytin-1.”

Johns Hopkins Medicine also describes the two spike proteins as “completely different.”

“It's like saying you and I both have the same social security number because they both contain the number five. So that was wrong to begin with,” said Dr. Paul Offit with the Vaccine Education Center at the Children's Hospital of Philadelphia in a YouTube video debunking the claim.

The mRNA vaccines also can not alter your DNA and affect fertility that way either. Pediatrics and molecular virology professor, Dr. Peter Hotez with the National School of Tropical Medicine, told ABC News: “There’s no plausible mechanism by which that could occur.”

Misleading claims and opposition to the vaccine, especially for young adults and children, by controversial political advocacy groups including the Association of American Physicians and Surgeons and America’s Frontline Doctors, have also helped fuel misinformation around the vaccine’s safety.


The American College of Obstetricians and Gynecologists (ACOG), the Society for Maternal-Fetal Medicine (SMFM), and the Centers for Disease Control and Prevention (CDC) all say there is no evidence the vaccines will affect fertility. 

In studies conducted on animals prior to its authorized use, the mRNA vaccines were found not to have an effect on fertility or cause problems with pregnancy.

Johns Hopkins also noted that during the Pfizer vaccine tests, 23 volunteers involved in the trials became pregnant and the only one who suffered a miscarriage had actually received the placebo, not the mRNA vaccine.

Sankar said participants in the clinical trials were told not to get pregnant, but some inadvertently did anyway and carried their babies to term.

“We have data from real world evidence that suggest the vaccine would not affect pregnancy or fertility,” she said.

In his YouTube video, Offit also pointed to two clinical trials that were conducted on the mRNA vaccines where a similar number of women became pregnant in the vaccine group and the placebo group.

“Now, if it was true that this vaccine or these vaccines affected fertility, then there should have been more pregnancies in the placebo group than in the vaccine group, but that wasn't true...the vaccine didn't enhance fertility and it didn't negatively affect fertility,” Offit said.


Some of the renewed concerns with children involve worries about the lasting effects of the COVID-19 vaccines on fertility.

“The vaccine itself is not going to do anything. It goes into a body very temporarily to just basically ignite or elicit an immune response, and our body’s the one that then takes over and does all the work,” said Sankar.

She explains that the components within a vaccine do not stick around for long. The mRNA for example, degrades extremely quickly. These vaccines “teach” our cells to make the spike proteins that will trigger an immune response. Once the proteins are created, the mRNA “instructions” break down and are discarded. Sankar says they are typically gone within 48 to 72 hours. Nothing accumulates in any organ.

“The vaccine and even the memory cells and antibodies don’t stick around forever at all,” she added, explaining that is why many vaccines require booster shots.


To be clear, all the normal regulatory requirements and steps to develop a vaccine took place, including the clinical trials and number of participants normally required, SickKids says on its website. A key reason why researchers were able to complete everything so quickly was due to the large number of COVID-19 cases in the trials, how quickly they were able to get volunteers, and the enormous amount of financial, staffing, and technical resources that were quickly made available due to the urgency of the pandemic. These are all elements that would normally take much longer to come together in a pre-pandemic environment.

Even with that urgency, Sankar also pointed to a wealth of historical data and decades of scientific research and expertise around vaccines in general that also served as an useful template for what scientists may or may not expect.

“It’s important for people to realize that science and research has been going on for many, many years. You’re only now in a pandemic, so everything is new. but just because we are studying something that is new now, it doesn’t mean that we don’t have the tools and research from years of experience,” she said.

“For many of the vaccines that have been administered to children, there hasn’t been any evidence to suggest there was any kind of effect on the fertility of girls or young people who would want to eventually become pregnant.”