BACKGROUND AND PURPOSE:

• Some people on social media have claimed that there is an alleged similarity between syncytin-1 and the SARS-CoV-2 spike protein which, through immune cross-reactivity, could lead to female sterility
• Morris (F&S Reports, 2021) used frozen embryo transfer to compare the implantation rates between SARS-CoV-2 seropositive vs seronegative women

METHODS:

• Cohort study
• Participants
  • Women undergoing frozen embryo transfer (FET)
• Exposures
  • Seropositive due to vaccination (Pfizer or Moderna)
  • Seropositive due to natural infection
  • Seronegative
• Study design
  • Levels of SARS-CoV-2 IgG were determined from serum samples obtained prior to FET
  • All transfers used a single expanded blastocyst in a hormone-prepared uterus
  • Transfer was performed under transabdominal ultrasound guidance
• Primary outcomes
  • Embryo implantation rates
    • Serum hCG level of >5 mIU/mL obtained 8 days after transfer, followed by a rising level two to three days later
  • Sustained implantation rates
    • Presence of ultrasound visualized fetal heart tones at two time points at least one week apart

RESULTS:

• 148 patients
  • Seropositive: 37.8%
    • Due to vaccination: 64.8%
    • Due to natural infection: 35.2%
  • Baseline characteristics were similar between exposure groups, except for higher mean BMI in the post-infection group than the vaccinated group and the nonreactive group (P = 0.005)
• There was no difference in embryo implantation rates between the groups (P=0.99)
  • Vaccine seropositive: 80.0%
  • Infection seropositive: 73.7%
  • Seronegative: 73.9%
• There was also no difference in sustained implantation rates between the groups (P=0.99)
  • Vaccine seropositive: 65.7%
  • Infection seropositive: 47.4%
  • Seronegative: 52.3%

CONCLUSION:

• SARS-CoV-2 seropositivity, whether from vaccination or infection, does not prevent embryo implantation or early pregnancy development
• Claims that SARS-CoV-2 spike protein may induce cross-reactivity with syncytin-1 appear unfounded
• The authors state

Physicians and public health personnel can counsel women of reproductive age that neither previous illness with COVID-19 nor antibodies produced from vaccination to COVID-19 will cause sterility

Learn More – Primary Sources:

SARS-CoV-2 spike protein seropositivity from vaccination or infection does not cause sterility