This case was reported by a nurse via call center representative and described the occurrence of underdose in a 39-year-old female patient who received ENGERIX B pediatric (batch number ZT59G, expiry date 14th February 2016). On an unknown date, the patient received ENGERIX B pediatric .5 ml. On an unknown date, an unknown time after receiving ENGERIX B pediatric, the patient experienced underdose and inappropriate age at vaccine administration. On an unknown date, the outcome of the underdose and inappropriate age at vaccine administration were unknown. Additional details were provided as follows: The adult patient received pediatric dose of ENGERIX B, which led to an underdose and an inappropriate age at vaccine administration. Follow up received on 30th June 2015 from nurse: This case was identified as duplicate of US2015094167. Case US2015094167 was deleted and all the future correspondence will be added in the present case which stands as case of record for this patient. The duplicate case included additional following information: The patient was pregnant at the time of vaccination. The patient's delivery was due in January. The patient had inadvertently received ENGERIX B (10 mcg), which led to accidental underdose and inappropriate age at vaccine administration. No further information was available. Follow up information received on 3rd February 2016 from nurse as follows: The patient demographics were updated. The patient's date of last menstrual period was 18th April 2015 and estimated date of delivery was 23rd January 2016. On 30th April 2015, the patient received 1st dose of ENGERIX B adult (1 ml, intramuscularly, batch number: 7S29F), at 12 days after last menstrual period (before conception). On 22nd June 2015, the patient accidentally received 2nd dose of ENGERIX B as pediatric dose, which also led to lengthening of the vaccination schedule. The reporting nurse called to GlaxoSmithKline medical immunization specialist physician and received an information regarding CDC recommendation to revaccinate the patient. The physician gave order to revaccinate the patient with adult dose of ENGERIX B. On 2nd July 2015, the patient was revaccinated with the adult dose of ENGERIX B (1 ml, intramuscularly, batch number: 7S29F), as 2nd dose in series at 10 weeks and 3 days and during 1st trimester of the pregnancy. On 30th October 2015, the patient received 3rd dose of ENGERIX B adult (1 ml, intramuscularly, batch number: 7S29F), at week 27 and 6 days and during 2nd trimester of pregnancy. This led to shortening of the vaccination schedule. The VAERS details were updated. [Pregnancy Notes]: On 22 March 2016, this case was considered lost to follow-up. Follow up information received on 23rd May 2016 from nurse: This case was upgraded to serious due to spontaneous abortion (GSK medically significant). The number of fetuses was 1. The reporter details were updated. On 30th April 2015, the patient received 1st dose of ENGERIX B adult, which was received before pregnancy. Between 15th June 2015 to 21st June 2015, approximately 46 days after the 1st dose of ENGERIX B adult, the patient had spontaneous abortion at 8 weeks of gestation. The cause of miscarriage was unknown. No other facts were known by the reporter. On 2nd July 2015, the patient received 2nd dose (corrective dose) of ENGERIX B, which led to lengthening of the vaccination schedule. The event vaccine exposure during pregnancy was removed, because the patient experienced spontaneous abortion before administration of 2nd and 3rd doses.