Do the COVID-19 vaccine candidates risk inducing infertility in women?

Question

Dr. Wolfgang Wodarg and Dr. Michael Yeadon wrote a request to the European Medicines Agency (EMA) on December 1, 2020, demanding that progress on the vaccine candidates be stopped until alleged flaws in the trials are remedied.

(Some sources falsely claim Yeadon was "head of research" in Pfizer. Snopes refute this, and say he was a "vice president and chief scientist for allergy and respiratory". Snopes also criticizes each of the two for false statements about COVID-19 in the past.)

In section "C" ("STATEMENT OF GROUNDS") in point "XI" there is a claim about fertility:

Several vaccine candidates are expected to induce the formation of humoral antibodies against spike proteins of SARS-CoV-2. Syncytin-1 (see Gallaher, B., “Response to nCoV2019 Against Backdrop of Endogenous Retroviruses” - http://virological.org/t/response-to-ncov2019-against-backdrop-of-endogenous-retroviruses/396), which is derived from human endogenous retroviruses (HERV) and is responsible for the development of a placenta in mammals and humans and is therefore an essential prerequisite for a successful pregnancy, is also found in homologous form in the spike proteins of SARS viruses. There is no indication whether antibodies against spike proteins of SARS viruses would also act like anti-Syncytin-1 antibodies. However, if this were to be the case this would then also prevent the formation of a placenta which would result in vaccinated women essentially becoming infertile. To my knowledge, Pfizer/BioNTech has yet to release any samples of written materials provided to patients, so it is unclear what, if any, information regarding (potential) fertility-specific risks caused by antibodies is included.

According to section 10.4.2 of the Pfizer/BioNTech trial protocol, a woman of childbearing potential (WOCBP) is eligible to participate if she is not pregnant or breastfeeding, and is using an acceptable contraceptive method as described in the trial protocol during the intervention period (for a minimum of 28 days after the last dose of study intervention).

This means that it could take a relatively long time before a noticeable number of cases of postvaccination infertility could be observed.

Is there is a significant chance that antibody response against spike proteins of SARS-CoV-2 could result also in antibody response against syncytin-1 and cause infertility?

Answer 1

I believe that I can answer my own question, since user "Fizz" already answered almost the same question that I posted on medicalsciences.stackexchange.com - Is there a reason to be anxious about claim that COVID-19 vaccine could turn out to be inducing infertility in females?

According to experts quoted by AP:

while syncytin-1 and the spike protein broadly share some features, they are quite different in the details that antibodies recognize.

Aside from the fact that COVID-19’s spike protein and syncytin-1 are viral fusion proteins that cause membrane fusion, they are not related at all, Dutch said.

also:

We don’t see infertility with the flu vaccine and that is also targeting a viral fusion protein in a similar way that the spike is a viral fusion protein of the coronavirus

source

It seems like the risk of said infertility is improbable and I personally believe that such statement was made just to harm vaccine effort and spread fear, especially when we take into account the fact that authors of this statement were spreading misinformation about COVID in the past.

Head to the post on medicalsciences that I linked above, for more thorough answer.