Exposure to influenza virus; Vaccine exposure during pregnancy; This is an observational study case from, initially received on 09-Dec-2019, concerning a 21-year-old female, pregnant subject of body weight: 219 lbs, height: 63 inches and body mass index (BMI): 38.8, who was enrolled in a prospective observational safety study.  The subject's medical history included bipolar disorder, obesity, type 2 diabetes mellitus, depression, anxiety and high risk pregnancy (history of miscarriage).    The subject's concomitant medications included Prenatal vitamins (unspecified minerals and vitamins) as a vitamin, Makena (hydroxyprogesterone caproate) for high risk pregnancy (history of preterm labor), metformin and Lantus XR (insulin glargine), both for type 2 diabetes mellitus.  The subject had two previous pregnancies with one preterm live birth and one spontaneous abortion (history of miscarriage). The subject had no history of offspring with major congenital malformation (MCM). The subject had no maternal or paternal history with MCMs. The subject did not have a prior history of use of tobacco or alcohol during pregnancy. For an unspecified amount of time during pregnancy, the subject used cannabis.   The subject's last menstrual period (LMP) date was 23-Aug-2019. The type of pregnancy was singleton. The subject's estimated delivery date (EDD) and corrected EDD (CEDD) were reported as 29-May-2019.  On 04-Nov-2019, at approximately 10 weeks of gestation, the subject was administered Flucelvax Quadrivalent (Flu Vaccine Cell Subunit QIV) [influenza vaccine, subunit influenza virus vaccine polyvalent, dose: 0.5 ml, batch number: 261223, route of administration, expiry date and anatomical location: not reported] (explicitly coded as Vaccine exposure during pregnancy') for an influenza immunisation.  On 18-Nov-2019, first trimester screen and nuchal translucency were performed, and no MCM was noted.   On 26-Nov-2019, 22 days after vaccination, the subject experienced exposure to influenza virus and started treatment with Tamiflu (oseltamivir) at a dose of 75 mg, administered once daily, via oral route of administartion.    On 17-Dec-2019, the subject underwent maternal serum alpha-fetoprotein screening (MSAFP) / serum markers and second trimester screen and no MCM was noted.  On 20-Dec-2019, the subject underwent ultrasound check cervical length, and no MCM was noted.   On 06-Jan-2020, treatment with Tamiflu was stopped.   On 17-Jan-2020, the subject underwent anatomy ultrasound and no MCM was noted.   On an unspecified date, pregnancy status was collected, and no pregnancy complications were noted.   At the time of this report, the outcome of event exposure to influenza virus was not reported.   The event of exposure to influenza virus was assessed as serious due to the criterion of medical significance.   The reporter did not provide causality assessment.  Follow up information received from other health professional on 11-Feb-2020 included: Patient's medical history and laboratory tests updated. Makena added as concomitant medication. Event exposure to influenza virus added. Case was upgraded from non-serious to serious, the classification special case with no AE was deleted and Tamiflu was amended to treatment medication. Narrative was amended accordingly.  Company comment: Exposure to influenza virus was assessed as possibly related to the vaccine (defaults to 'related' causality for reporting purposes). Exposure during pregnany was assessed as unrelated in line with internal guidelines.; Sender's Comments: Exposure to influenza virus was assessed as possibly related to the vaccine (defaults to 'related' causality for reporting purposes). Exposure during pregnany was assessed as unrelated in line with internal guidelines.