In the past few weeks, people who speak out against Covid vaccinations have been making a claim that is not only false but also contradicts the rules of biology: Being close to someone who has received a vaccine can disrupt a woman’s menstrual cycle or cause a miscarriage.

The idea promoted on social media by accounts with hundreds of thousands of followers is that vaccinated people may dispense vaccine material and affect those around them as if it were second-hand smoke. This month, a Florida private school told staff that if they were vaccinated, they would not be able to interact with students because “at least three women have menstrual cycles after spending time with a vaccinated person.”

In reality, it is impossible to experience any effects from being around a vaccinated person as none of the vaccine ingredients are able to leave the body into which they were injected.

The vaccines currently approved for use in the United States instruct your cells to make a version of the spike protein found on the coronavirus so your immune system can learn to recognize it. Different vaccines use different vehicles to deliver the instructions – for Moderna and Pfizer, messenger RNA or mRNA; for Johnson & Johnson an adenovirus that has been genetically engineered to be inactive and harmless – but the instructions are similar.

“It’s not like it’s part of the virus or it does things that the virus does – it’s just a protein of the same shape,” said Emily Martin, an infectious disease epidemiologist at the University of Public Health Michigan. “It is not possible to transfer any of the vaccine from one person to another. That is simply not possible biologically. “

Microorganisms spread from person to person by replicating. The vaccine ingredients and protein cannot replicate, which means they cannot spread. They don’t even spread in your own body, let alone in others.

“They’re injected into your arm and that’s where they stay,” said Jennifer Nuzzo, an epidemiologist at Johns Hopkins, of the vaccines. “MRNA is absorbed by your muscle cells near the injection site. The cells use it to make this protein. The immune system learns about the spike protein and gets rid of these cells. It’s not something that’s floating around. “

Nor is it something that stands around. Messenger RNA is extremely fragile, which is one reason we’ve never had an mRNA-based vaccine before: it took scientists a long time to figure out how to use them for the brief amount of time it took to provide their instructions can remain intact. It disintegrates within a few days after vaccination.

Vaccinated people cannot shed anything because “there is nothing to shed,” said Dr. Céline Gounder, Infectious Disease Specialist at Bellevue Hospital Center and member of President Biden’s transition advisory team for the coronavirus. “The people who drop viruses are people who have Covid. So if you want to prevent yourself or other viruses from shedding viruses, the best thing to do is to get vaccinated so you don’t get Covid. “

This brings us to the reports of women with abnormal periods after being around vaccinated people. Since a person’s vaccine cannot affect anyone, it is impossible to link these two events together. Many things, like stress and infection, can disrupt the menstrual cycle.

The claims are “a conspiracy designed to weaken confidence in a number of vaccines that have been shown in clinical studies to be safe and effective,” said Dr. Christopher M. Zahn, vice president of practice activities at the American College of Obstetricians and Gynecologists, said in a statement. “Such conspiracies and false stories are dangerous and have nothing to do with science.”

Some women have raised concerns that vaccination could affect their menstrual cycles. In contrast to second-hand effects, this is theoretically possible and the research is not yet complete. However, anecdotal accounts could be explained by other factors, and no study has found an association between the vaccine and menstrual changes.

“There is no evidence that the vaccine affects your menstrual cycle in any way,” said Dr. Gounder. “It’s like saying that just because I got the vaccine today will we have a full moon tonight.”