Claim: The U.S. Centers for Disease Control and Prevention said the COVID-19 vaccines caused the largest carcinogenic exposure in history. Several social media posts made the claim on Facebook, including one that said "CDC admits COVID-19 vaccines are now the largest carcinogenic exposure in history. Some social media users may have been referring to a slide presentation uploaded to the CDC website, which outlined some uncertainties surrounding the COVID-19 vaccines. The note outlined concerns about the methodology the South Korean team followed to reach their conclusion, casting doubt on their findings. A third point the Belgian researchers made was that the South Korean study did not account for "surveillance bias."