Initial unsolicited misuse literature report received from a healthcare professional on 10-May-2015. Abstract: In this case report, we describe a 63-year-old female with Crohn's disease since age 16 years, and on adalimumab therapy, who inadvertently received a yellow fever vaccine (YFV) 4 days before her next dose of adalimumab. She had never received YFV. Her next dose of tumor necrosis factor (TNF) antagonist was held. She did not report any adverse effects referable to the vaccine. Reverse transcriptase-polymerase chain reaction (RT-PCR) for yellow fever (YF) viral RNA on days 12 and 18 postvaccination was negative. Neutralizing antibody to YF virus vaccine was immunoprotective on day 18 following vaccination, which further increased by day 26. A neutralizing antibody obtained 2 years following vaccination also remained immunoprotective. A 63 year old female patient had received a first dose of YELLOW FEVER VACCINE (Batch number, expiration date, dose, route and site of vaccination were not reported) on an unspecified date. It was reported that the patient received the vaccine four days prior to her next dose of adalimumab. The patient had a history of Crohn's disease since 16 years of age. She was also on adalimumab therapy. Concomitant medications were not provided. The patient inadvertently received yellow fever vaccine leading to accidental exposure to product. It was reported that her next dose of tumor necrosis factor (TNF) antagonist was held. Laboratory investigations included Reverse Transcriptase-Polymerase Chain Reaction (RT-PCR) for yellow fever (YF) viral RNA on days 12 and 18 post vaccination which was negative. Neutralizing antibody to YF virus vaccine was immunoprotective on day 18 following vaccination, which had further increased by day 26. The neutralizing antibody obtained 2 years following vaccination also remained immunoprotective. No adverse event was reported further. List of documents held by sender: none. Follow up literature report received from a physician on 25 May 2015. It was reported that, patient had medical history of Crohn's ileocolitis with perianal involvement since the age of 16 years and was being treated with tumor necrosis factor (TNF)-? antagonists (adalimumab). Over the years, patient was treated with corticosteroids, surgical resections for strictures and fistula formation, and ileal sigmoidostomy. Patient took corticosteroids till 1990s. As Crohn's at ileocolonic anastomosis reoccurred, patient was treated with infliximab 200 mg every 8 weeks from 2003 to 2008 and this was changed to adalimumab 40 mg every other week in 2008 for lifestyle reasons and remained in remission. It was reported that patient had received a first dose of 0.5 ml YF-Vax subcutaneously on 01 December 2011 for travel to a yellow fever (YF)-endemic area 4 days before she was due for her next dose of adalimumab. It was reported that patient had not received YF-Vax in the past. Patient was advised not to take the dose of adalimumab and also instructed to contact the clinic immediately if she developed flu-like or other symptoms of acute illness during the following weeks. The patient remained asymptomatic for about two and half weeks. 18 days after vaccination, patient reported an increased frequency of loose bowel movements. Over the next 8 days her bowel movement increased significantly and 26 days after vaccination patient had more than 20 loose bowel movements a day. The patient was followed up by her gastroenterologist who resumed adalimumab with loading doses of 80 mg subcutaneously on days 35, 36, and 49 post vaccination. Serum specimens were obtained on days 12, 18, and 26 following vaccination and were analyzed for YF viral RNA and neutralizing antibodies against YF virus. Laboratory testing revealed no YF viral RNA on days 12 and 18 following vaccination and the presence of YF-neutralizing antibody on days 18 and 26 following vaccination (titers were 80 and 640, respectively), and RT PCR was negative on 12 and 18 days. YF-neutralizing antibody titer obtained 24 months following vaccination was 160. After 7 days of restarting the adalimumab, patient diarrhea almost resolved and continued to take adalimumab 40 mg subcutaneously every 2 weeks on day 63 post vaccination and continued to do well. List of documents held by sender: none.