18yo presented to ED for anaphylactic reaction to Yellow Fever Vaccine.  Treated in ED and admitted for observation and leukocytosis. Of note, this event was captured as a PSR at time of event (admitting physician) due to vaccination staff not following SOP to administer pre-screening questionnaire or watching patient post vaccination. Site was notified and conducted internal investigation. Capturing here for ADR data given anaphylactic rxn.    ADR investigation ? Preventable ADR, Level 4 severe reaction requiring treatment and admission.  Patient had a known egg allergy, a contraindication to the Yellow Fever Vaccine, however the pre-screening questionnaire was not conducted to gather this information prior to administration.  ED/Admitting physician notes also annotate it is unclear why patient received YFV given no upcoming travel location requiring the vaccine.  No PCM listed in portal, however facility made aware of incident. Allergy added to profile at time of event.  Reaction submitted to VAERS at time of this report.   Of note, admission note says vaccine administered IM in tricep, vaccine administration documentation shows SubQ left arm.  Vaccine was also given to patient with history of anaphylaxis to eggs -- pre-screening questionnaire was not administered prior to vaccine administration.    Admission note: male who presented to the ER today with complaints of chest tightness and wheezing after having a yellow fever vaccine about 2 hours prior to arrival.  He also had wheezing facial swelling and urticaria.  On arrival to the ER he was satting at 77% on room air.  He initially required 12 L nonrebreather facemask and was eventually weaned to room air. Patient endorses an egg allergy that includes symptoms of facial swelling and vomiting.  She also reports a history of asthma as a child and stopped taking medications age 13.  He denies any hospitalizations or intubations for asthma.  He states his unit had him get the yellow fever vaccine as a part of readiness.  States he is going to leave in another state.  He denies any upcoming travel.  On time of exam he denied cough, shortness of breath, chest pain, chest tightness, rash or facial swelling.  States he is back at his baseline.  #Anaphylactic reaction: Patient with anaphylactic reaction after to yellow fever vaccine administered intramuscularly in the tricep. Likely occurred secondary to presumed egg allergy, based on description of facial edema and vomiting occurring every time after patient eats eggs.  It is unclear why the patient had the yellow fever vaccine as he is not traveling to any endemic areas in the near future.  We will continue to monitor for delayed reaction versus recurrent anaphylactic reaction.  --Telemetry  --Continue scheduled Benadryl 50 mg every 6 hours  --Famotidine 20 mg daily  --Continued prednisone for a total of 5 days of steroids  --EpiPen on hand  --PRN duo nebs for wheezing or shortness of breath  --Consider allergy consult for further management of egg allergy in his occupation   #Leukocytosis: Patient with white count of 17.3 on admission.  He has been afebrile and vital signs have normalized since treatment of anaphylaxis.  Suspect this is secondary to demargination of white blood cells after receiving steroids.  Additionally patient has no other signs or symptoms of infection. Will continue to monitor with daily CBCs as well as monitoring of vital signs.  -- qAM CBC