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?