An unmasking phenomenon in an observational post-licensure safety study of adolescent girls and young women

Vaccine. 2012 Jun 29;30(31):4585-7. doi: 10.1016/j.vaccine.2012.04.103. Epub 2012 May 11.


Our recent experience in a post-licensure safety study of autoimmune conditions following the quadrivalent human papillomavirus vaccine in 189,629 girls and young women ages 9-26 years led us to question the adequacy of the exclusion of Day 0 events to prevent the erroneous association of prevalent conditions with vaccination. Of the 18 confirmed cases of Graves' disease diagnosed in days 1-60 following vaccination, only 6 cases appeared to be truly new onset. Among the remaining 12 cases, 2 cases had abnormal thyroid stimulating hormone or thyroxine labs drawn prior to or on Day 0 but had no documented pre-existing symptoms. The other 10 cases had mention of symptoms of hyperthyroidism referencing a period prior to first HPV-4 dose. This 'unmasking' phenomenon, due to health care visits that include vaccination and new workups of preexisting symptoms, may not be adequately controlled through the exclusion of Day 0 events.

MeSH terms

  • Adolescent
  • Adult
  • Autoimmune Diseases / chemically induced
  • Autoimmune Diseases / diagnosis*
  • Child
  • Drug Evaluation
  • Drug-Related Side Effects and Adverse Reactions
  • Female
  • Graves Disease / chemically induced
  • Graves Disease / diagnosis
  • Humans
  • Papillomavirus Vaccines / adverse effects*
  • Product Surveillance, Postmarketing*
  • Young Adult


  • Papillomavirus Vaccines