Initial unsolicited report received from the literature on 29-Jul-2016. This case is linked to cases 2016SA140361, 2016SA140962, 2016SA140455, 2016SA140480, 2016SA140494, 2016SA140516, 2016SA140980, 2016SA140990, 2016SA141005, 2016SA141097, 2016SA141105 (same literature). Background: No comparative review of Vaccine Adverse Event Reporting System (VAERS) submissions following pandemic influenza A (H1N1) 2009 and seasonal influenza vaccinations during the pandemic season among one population has been published. Methods: We compared two populations adverse event reporting rates. Adverse events (AEs) following vaccination were identified from VAERS for adults aged 17-44 years after pandemic (monovalent influenza [MIV], and seasonal (trivalent inactivated influenza [IIV3], live attenuated influenza [LAIV3]) vaccines. The first population vaccination coverage was provided by the Medical Surveillance System. The second population vaccination coverage was estimated using data from the National 2009 H1N1 Flu Survey and the Behavioral Risk Factor Surveillance System survey. Results: Vaccination coverage was more than four times higher for MIV and more than twenty times higher for LAIV3 in the first population than in the second population. The reporting rate of serious AE reports following MIV in the first population (1.19 per 100,000) was about half that reported by the second population (2.45 per 100,000). Conversely, the rate of serious AE reports following LAIV3 among the first population (1.32 per 100,000) was more than twice that of the second population. Although fewer AEs following MIV in the first population were reported overall, the rate of Guillain-Barre Syndrome (GBS) (4.01 per million) was four times greater than that in the second population. (1.04 per million). Conclusions: Despite higher vaccination coverage in the first population, the rate of serious AEs following MIV was about half that in the second population. The rate of GBS reported following MIV was higher in the second population. This case involves a 40-year-old male patient (age unspecified) who was vaccinated with a dose of Monovalent H1N1 Vaccine (batch number, expiry date, dose, dose in series, route and site of administration were not reported) on an unspecified date. Patient's medical history was reported as MRI of brain was done previously which showed no acute abnormality but frontal lobe encephalomalacia possibly remote trauma which was not documented. Concomitant medications were not reported. On an unknown date, three days following the vaccination, patient developed GBS\Guillain-Barre syndrome, weakness bilaterally arms and legs, numbness, paresthesias, metallic taste. Laboratory tests including CSF (result reported as positive albumin cytologic dissociation), Electromyography (result: positive for demyelination), CTs & MRIs brain, cervical & lumbar spine, USD abdomen, heavy metal screen, EBV (Epstein-Barr virus) serology (result: negative) and Cytomegalovirus (CMV) immunoglobulin M (IgM)/ immunoglobulin G (IgG) (result: positive). Patient received corrective treatment with IVIG, Solumedrol, Acyclovir for CMV. The outcomes of events were not reported. Upon internal review the case was considered as serious because of important medical event Guillain-Barre syndrome. Documents held by sender: none. Sender's Comments: Patient had Guillain-Barre syndrome 3 days following MONOVALENT INFLUENZA A (H1N1) 2009 VACCINE. Time to onset is compatible with the vaccine, Guillain-Barre syndrome is usually preceded by upper respiratory tract or gastrointestinal tract infection, viral infection and vaccination, in this case patient has history of recent CMV (cytomegalic virus) infection with acute on chronic hepatitis, also monoclonal gammopathy of unknown significance and also patient was vaccinated with influenza vaccine which is also one of the triggering factors, patient is also positive for demyelination on EMG and Positive albumin cytologic dissociation in CSF . Detail medical history, past vaccination history and its tolerance are needed to further assess the case. Based on the available information the role of vaccine cannot be excluded.