Tue 2021-Aug-17

COVID-19 Vaccines and Infertility: Analyzing the Myth

Tagged: COVID / JournalClub / MathInTheNews / PharmaAndBiotech / Politics / SomebodyAskedMe

Somebody asked me about whether the COVID-19 vaccine could cause infertility. Wait, what?

It’s not always the wrong question

The people who asked me are in a family where the grandparent generation were prescribed diethyl stilbestrol (DES) to prevent miscarriage. While well-intended, that synthetic estrogen drug had effects on female babies that made them more prone to a number of disorders, including some cancers. So it’s not impossible that some medical treatments can reach across generations.


  • the COVID-19 vaccines are not hormones directly affecting the reproductive system, like DES.
  • Also, DES was taken off the market 50 years ago: we’ve learned a lot from it (and how not to do it again).
  • Also also, episodes like that are so rare they are famous: DES and thalidomide come to mind as cautionary tales that everybody knows and takes precautions to prevent their re-creation.

So let’s look into the COVID-19 and infertility thing, but keep in mind we’re likely to find that it’s just a paranoid myth, not another DES in the making. That’s the evidence that might set minds at ease.

Some Paranoid Myths Around COVID-19 Vaccines

People say the damndest things.

In spite of all the effort to educate the public, there are a dozen or so superspreaders of misinformation poisoning the well, telling people that the vaccines somehow:

  • Change your DNA, inserting lizard space alien sequences
  • Make you magentic
  • Make you receive 5G signals so the government can reprogram you
  • Make you autistic
  • Make you more submissive to authority
  • Give you COVID-19
  • Insert a tracking chip (unlike your cell phone, which already tracks you)
  • Are the Number of the Beast
  • … and too many more to catalog without becoming ill.

They mention every conceivable notion – and a good many inconceivable ones – except the one that matters: the vaccines will make you unlikely to be hospitalized with COVID-19 or die with COVID-19!

Today’s knuckleheadery, though, is the myth that the COVID-19 mRNA vaccines could make you sterile, allegedly due to some dingbattery about population control variously attributed to George Soros and Bill Gates.

Leaving aside the George Soros and Bill Gates stuff which always seems to crop up, let’s just think for a moment:

If I am pregnant, can I get a COVID-19 vaccine?

Yes, COVID-19 vaccination is recommended for all people 12 years and older, including people who are pregnant, breastfeeding, trying to get pregnant now, or might become pregnant in the future. You might want to have a conversation with your healthcare provider about COVID-19 vaccination. While such a conversation might be helpful, it is not required before vaccination. Learn more about vaccination considerations for people who are pregnant or breastfeeding.

If you are pregnant and have received a COVID-19 vaccine, we encourage you to enroll in v-safe, CDC’s smartphone-based tool that provides personalized health check-ins after vaccination. A v-safe pregnancy registry has been established to gather information on the health of pregnant people who have received a COVID-19 vaccine.

The Bad Seed

Let’s dig in a bit deeper, and try to figure out whence this particular paranoid fantasy came. These things usually grow from a bad seed somewhere.

First we’ll look through this nice bit of public science communication [1] from “ZDoggMD”, the pseudonym of Zubin Damania, a Stanford-trained hospitalist, now a clinical assistant professor of medicine at UNLV. The high points:

  • Spike protein is alleged to cause miscarriages because of sequence similarity to syncytin-1 in the placenta. In other words, they think the spike protein will give you a never-before-seen autoimmune disease where antibodies attack the placenta. Factually false: using BLASTP, you can check for yourself. But I won’t bother:
    • the “similarity” is only 4 amino acids long, while UniProtKB tells me syncytin-1 is 538 AA long,
    • it’s in a non-functional position,
    • the antibodies don’t bind there.
  • Logical fallacies: Natural COVID would also sterilize, if this syncytin-1 theory were true. Antibodies from natural immunity and from vaccination are pretty alike. Natural COVID doesn’t cause sterility.
  • Somehow vaccinated people shed spike protein, to sterilize women around them. ZDoggMD described this as “a new low”. Moving the goalposts is a common feature of conspiracy theories. If you debunk one claim, they just retreat to another. If vaccine doesn’t do it to you, you’ll somehow do it to others through “protein shedding” which has never been observed before.
  • The “expert” being cited is Sherri Tenpenny. She’s a former osteopath, with no training in immunology. She’s now a professional anti-vaxxer, and even makes money with a course to train other anti-vaxxers. Fake experts is another sign of conspiracy theories.
  • There’s no known mechanism for protein shedding. It has never been seen in any other vaccine, nor in protein-based drugs. It’s only present in a small area of your arm muscle, not the whole body. It’s only there 24-48 hours and has no way to get out of your body and into someone else’s. There’s no mechanism to cause sterility. Magical thinking like this is another symptom of craziness.
  • Conspiracy thinking: Point to some dark forces that secretly want to harm you: sterilize because of something-something Bill Gates, or Big Pharma doesn’t want you to know so they can sell you a cure. (Though that’s ironic, because Tenpenny is literally selling the conspiracy.)
  • Cherry-picking data: You can always find 1 paper in the literature saying just about anything, e.g., here about syncytin-1. But the consensus of all the rest of the literature is “no”. It’s all just confirmation bias.

They almost make it too easy, by ticking off all the checkboxes of conspiracy thinking (in bold above): factually false statements, logical fallacies, moving the goalposts, fake experts, magical thinking, conspiracy tropes, and cherry-picking data. Le sigh.

What else ya got?

Ok, that’s pretty damning. And Damania is quite highly experienced and eloquent, but he’s just one guy. Can we find evidence in the scientific (and other) literature that agrees with him?

Why, yes. Yes, we can.

Reuters Fact Check: vaccines do not target syncytin-1 A “Fact Check” article on Reuters [2] confirms that the root of this conspiracy theory is the alleged link between SARS-CoV2 spike protein and syncytin-1, which in fact does not exist. It describes the two proteins as “not very similar”, matching in only 4 amino acids out of the 538 in syncytin-1. (I wonder what’s the probability of getting a 4AA match between any 2 random proteins?) Verdict: FALSE.

Functional characterization of syncytin-1 A 2004 review will tell you all you want to know about syncytin-1 and its functional characteristics. [3] Oddly, syncytin-1 is a human endogenous retrovirus protein itself! Sometime in the distant past, a primate caught an endovirus which wrote some of its DNA into said primate. Our bodies have subsequently learned to use it. Biology is weird.

Lifehacker: Not getting vaccinated in pregnancy is the riskier choice CDC Media Statement: COVID-19 vaccines safe in pregnancy CDC Guidance: COVID-19 vaccines while pregnant or breastfeeding Zauche: mRNA vaccines preconception and in pregnancy do not raise miscarriage rates NEJM: mRNA COVID-19 vaccines safe for pregnant persons AJOG: vaccines effective in pregnant people, even for baby A more popular-literature article from LifeHacker [4] gives us the very good news that vaccination is safe, even while pregnant. As usual, they give nice references to the actual scientific literature.

They first point to a CDC media release officially declaring the COVID-19 vaccines safe for pregnant people. [5] It’s much riskier not to vaccinate. The CDC has, accordingly, updated their official advice recommending COVID-19 vaccination during pregnancy or breastfeeding. [6]

A preprint from another study [7] compared miscarriage rates between vaccinated and unvaccinated populations, and found no difference.

Another study published in the New England Journal of Medicine [8] followed over 35,000 people. They found rates of pregnancy loss, premature birth, and small birth weight were no different from pre-COVID studies, i.e., the vaccines don’t hurt anything.

A very clever study published in the American Journal of Obstetrics & Gynecology [9] worked the problem in the other direction: let’s assume the vaccine is safe for pregnant people, so check if it still works as a vaccine, i.e., that pregnancy doesn’t mess up the vaccine efficacy. The answer is cheering: yes, it’s effective, and as a bonus the babies retained some antibodies for SARS-CoV2 after birth. (This has been seen for other vaccines. Many doctors recommend a pertussis shot (TDaP) during pregnancy.)

So the verdict is very, very clear: vaccines not only do not cause infertility, they are warmly recommended by the CDC, the American College of Obstetricians and Gynecologists, and the Maternal-Fetal Medicine Society.

The Weekend Conclusion

Health in Pictures: Satirical Vaccine Cartoon from 1930s Get vaccinated. Don’t be like these guys, from a political cartoon in the 1930s. (Snopes says it’s real.)

It’s a satire from a 1930s pamphlet called “Health in Pictures”, though the name of the artist has been lost. It was in the context of efforts to eradicate smallpox, earlier in the 20th century. They have climbed a cliff of misinformation, and are about to plunge to their deaths in a sea of smallpox.

Yeah… don’t be these guys. I’d like to keep my fantasy that in the intervening century we may have learned something. Please don’t disabuse me of that.


Addendum 2021-Sep-08: Ivermectin and infertility

Late addendum, I know. But this is just too good to pass up.

Ivermectin is an antihelminthic medication (“de-wormer”) used mostly on horses, cattle and sheep. There is a human version for intestinal worms, and a topical version for smearing on the scalp if you have head lice. Fair enough, so far.

For essentially superstitious reasons, the right-wing conspiracy nuts think it’s a “secret” cure for COVID-19 that Big Bad Pharma doesn’t want you to know about. As a result they’ve been filling up poison control units by eating doses fit for horses. They’re afraid of real prevention by vaccines because they think they’ll become infertile, but… it turns out there’s an old study that shows ivermectin caused infertility due to poor sperm quality in 85% of the men who took it (NB: the original tweet seems to have been deleted as of 2021-09-08 9:00pm; Snopes says it isn’t credible):

Fecke @ Twitter: Ivermectin and male infertility

Eckman @ Twitter: Snopes debunks ivermectin & male infertility

Ah, well. It’s so hard to resist a slice of schadenfreude pie.

Notes & References

1: Z Damania, “Is Vaccine ‘Shedding’ A Threat To Unvaccinated Women? A Doctor Explains”, ZDoggMD on Youtube, 2021-Apr-27.

2: Reuters Staff, “Fact check: Available mRNA vaccines do not target syncytin-1, a protein vital to successful pregnancies”, Reuters, 2021-Feb-04.

3: C Chang, et al., “Functional Characterization of the Placental Fusogenic Membrane Protein Syncytin”, Biol Reprod 71:6 (2004-Dec-01), 1956-1962. DOI: 10.1095/biolreprod.104.033340.

4: B Skwarecki, “New Data Shows Not Getting Vaccinated in Pregnancy Is the Riskier Choice”, Lifehacker, 2021-Aug-12.

5: CDC Media Relations, “New CDC Data: COVID-19 Vaccination Safe for Pregnant People”, Centers for Disease Control and Prevention media statement, 2021-Aug-11.

6: CDC Staff, “COVID-19 Vaccines While Pregnant or Breastfeeding”, Centers for Disease Control and Prevention, updated 2021-Aug-11.

7: LH Zauche, et al., “Receipt of mRNA COVID-19 vaccines preconception and during pregnancy and risk of self-reported spontaneous abortions, CDC v-safe COVID-19 Vaccine Pregnancy Registry 2020-21”, preprint on Research Square, 2021-Aug-09. DOI: 10.21203/rs.3.rs-798175/v1.

8: TT Shimabukuro, et al., “Preliminary Findings of mRNA Covid-19 Vaccine Safety in Pregnant Persons”, New England Journal of Medicine 384:24 (2021), 2273-2282. DOI: 10.1056/NEJMoa2104983.

9: KJ Gray, et al., “Coronavirus disease 2019 vaccine response in pregnant and lactating women: a cohort study”, Am J Ob Gyn, 2021-Mar-25. DOI: 10.1016/j.ajog.2021.03.023

Published Tue 2021-Aug-17

Gestae Commentaria

Comments for this post are closed pending repair of the comment system, but the Email/Twitter/Mastodon icons at page-top always work.