Delivery at 36,7 weeks of gestation; Vaccine exposure during pregnancy; Bacterial vaginosis; This observational study case, initially received on 30-Nov-2020 from other health professional and concerned a 33-year-old, female, pregnant subject of body weight: 148 lbs, height: 62 inches and body mass index (BMI): 27.1, enrolled in, a prospective observational study.  The subject's concurrent condition included body mass index high. The subject's past medical history included bacterial vaginosis. The subject's  concomitant medications included OB complete one (fish oil, doconexent, icosapent, calcium ascorbate, cholecalciferol, alpha.-tocopherol acetate, d-, thiamine mononitrate, riboflavin, niacinamide, pyridoxine hydrochloride, folic acid, cyanocobalamin, biotin, calcium threonate, calcium malate, calcium carbonate, iron, ferrous asparto glycinate, potassium iodide, magnesium oxide, zinc oxide, and cupric sulfate capsule, liquid filled) for healthy pregnancy. The subject's past medications included Metrogel (metronidazole) and terconazole, both used for bacterial vaginosis.  The subject's obstetrical history included two previous pregnancies with one full term live birth, and one spontaneous abortion. The subject had no history of offspring with major congenital malformation (MCM). The subject had no relevant maternal and paternal medical history with MCM. The subject did not use tobacco, alcohol or illicit drugs during pregnancy.  The subject's last menstrual period (LMP) date was on 13-Apr-2020. The type of pregnancy was singleton. The estimated delivery date (EDD) was reported as 18-Jan-2021 and corrected estimated date of delivery (CEDD) was not reported.    On 06-Jul-2020, first trimester screen revealed no MCMs.  On 27-Jul-2020, second trimester screen revealed increased risk of Down syndrome, but no MCM was noted.   On 06-Aug-2020, amniocentesis revealed no MCMs.  On 07-Aug-2020, amniocentesis revealed no MCMs. The whole genome chromosome single-nucleotide polymorphism (SNP) microarray analysis was normal. No significant deoxyribonucleic acid (DNA) copy number changes or copy neutral regions within the 2.695 million region specific SNP.  On 04-Sep-2020, at approximately of 20 weeks of gestational age (calculated per LMP), the subject was vaccinated with Afluria Quadrivalent  (Flu Vaccine Egg Split QIV) (influenza vaccine, dose, route of administration, anatomical location: not reported) (explicitly coded as 'Vaccine exposure during pregnancy') for influenza immunisation. The batch number reported was P100239705.  On an unknown date in 2020, unknown amount of time after receiving Afluria Quadrivalent, the subject developed bacterial vaginosis.  On 02-Oct-2020, the subject started therapy with Metrogel 0.75 % cream (metronidazole), once at night, vaginally for bacterial vaginosis.  On 07-Oct-2020, the subject stopped treatment with Metrogel.  At gestational age of 36.7 weeks (as reported), the subject vaginally delivered, live birth female neonate. The characteristics of the neonate included birth weight of 2745 grams, head circumference was 33.5 centimeters (cm) and length 47.6 cm. Appearance, pulse, grimace, activity, and respiration (APGAR) scores at one and five minutes was 9. APGAR score for ten minutes was not reported. No MCM was identified at birth.   The outcome of events was not reported.   The reporter did not provide a causality assessment.  The event of 'premature delivery' was considered to be medically significant by a Physician within Seqirus' Pharmacovigilance and Risk Management Department.  This case is linked with 202101525 (the corresponding baby case).  Additional information received on 11-Dec-2020 from other health professional: Amniocentesis test results were provided. The narrative was amended accordingly.  Additional information received on 15-Jan-2021 from other health professional: The subject was enrolled in study upon data query resolution. Report type was changed. Subject's age was changed from 34 to 33 years. New amniocentesis test added in laboratory data. The narrative was amended accordingly.  Additional information received on 25-Feb-2021 from other health professional: Pregnancy outcome received, and pregnancy information updated. Stop date added and outcome changed from not reported to resolved for the event of 'vaccine exposure during pregnancy'. Premature delivery added as a new event and therefore, the case was upgraded from non-serious to serious. Link for baby case added. Narrative was amended accordingly.  Company comment: Premature delivery in a 33-year-old female subject was reported after vaccine exposure during pregnancy to the suspect product Afluria Quadrivalent. Vaccine was administered at approximately 20 weeks of gestational age, while the neonate was delivered at gestational age of 36.7 weeks. On an unknown date in 2020, the patient developed bacterial vaginosis. The patient's past medical history included bacterial vaginosis. The subject's obstetrical history included two previous pregnancies with one full term live birth, and one spontaneous abortion. The subject had no history of offspring with major congenital malformation (MCM). The subject had no relevant maternal and paternal medical history with MCM. The subject did not use tobacco, alcohol or illicit drugs during pregnancy. Vaccine exposure during pregnancy is assessed as unrelated per company's conventions. Bacterial vaginosis is assessed as not related due to biological implausibility and strong confounder (medical history). Causality for the event premature delivery is assessed as not related due to presence of significant confounding factor (bacterial vaginosis).; Sender's Comments: Premature delivery in a 33-year-old female subject was reported after vaccine exposure during pregnancy to the suspect product Afluria Quadrivalent. Vaccine was administered at approximately 20 weeks of gestational age, while the neonate was delivered at gestational age of 36.7 weeks. On an unknown date in 2020, the patient developed bacterial vaginosis. The patient's past medical history included bacterial vaginosis. The subject's obstetrical history included two previous pregnancies with one full term live birth, and one spontaneous abortion. The subject had no history of offspring with major congenital malformation (MCM). The subject had no relevant maternal and paternal medical history with MCM. The subject did not use tobacco, alcohol or illicit drugs during pregnancy. Vaccine exposure during pregnancy is assessed as unrelated per company's conventions. Bacterial vaginosis is assessed as not related due to biological implausibility and strong confounder (medical history). Causality for the event premature delivery is assessed as not related due to presence of significant confounding factor (bacterial vaginosis).