Suspected Vaccination failure; Acute respiratory infection; Influenza B virus infection; Cough; This case was reported in a literature article and described the occurrence of suspected vaccination failure in a infant patient who received Flu Seasonal QIV Dresden (Flu Seasonal QIV Dresden) for prophylaxis. Comparison of local influenza vaccine effectiveness using two methods. Vaccine 2021; 39(8): 1283-1289. DOI: 10.1016/j.vaccine.2021.01.013).   On an unknown date, the patient received Flu Seasonal QIV Dresden. On an unknown date, more than 2 weeks after receiving Flu Seasonal QIV Dresden, the patient experienced vaccination failure (serious criteria GSK medically significant), influenza b virus infection, acute respiratory tract infection (serious criteria GSK medically significant) and cough. On an unknown date, the outcome of the vaccination failure, influenza b virus infection, acute respiratory tract infection and cough were unknown.   It was unknown if the reporter considered the vaccination failure, influenza b virus infection, acute respiratory tract infection and cough to be related to Flu Seasonal QIV Dresden.  Additional details were provided as follows: This case was reported in a literature article and described the occurrence of Suspected vaccination failure, in a patient aged more than or equal to 6-month-old of unspecified gender, who was vaccinated with Unspecified Influenza vaccine (manufacturer unknown) for prophylaxis. This case corresponds to Table 3 reported in this literature article. The patient was a part of study that aimed at vaccine effectiveness (VE) estimates using methodology from the US Flu VE Network (research database) are compared with VE estimates using data from a clinical surveillance software system (administrative database). The advantages and disadvantages of both methods of estimating influenza VE are discussed. [The study took place in emergency departments, hospital-based clinics and outpatient primary and urgent care sites that are part of a large (40 hospital, 700 doctor's offices and outpatient sites) integrated health system]. The patient had not received antiviral medication in the 7 days before enrollment into the study. The patient belonged to administrative database group. No information on patient family history or concurrent condition or concomitant medication was reported.  On an unknown date, the patient received unspecified Influenza vaccine 2018-2019 season (administration site unspecified, dose not reported; batch number not provided). The age at vaccination was not reported. On an unspecified date, more than or equal to 14 days after vaccination, the patient presented with an acute respiratory infection (ARI) including cough within 7 days of symptom onset. Patient's respiratory specimen from nasopharyngeal and/or throat was taken for influenza virus testing by reverse-transcription polymerase chain reaction (RT-PCR). The patient had emergency department visit and was diagnosed with Influenza B infection. [In this study, Briefly, patients aged more than or equal to 6 months presenting with an acute respiratory infection (ARI) including cough within 7 days of symptom onset were enrolled at participating outpatient healthcare facilities, including community physician offices, urgent care centers and emergency departments. Respiratory specimens (nasal and throat swabs from patients aged more than or equal to 2 years or nasal swabs only from patients aged less than 2 years) for influenza virus testing (including virus type and subtype) by RT-PCR. The influenza circulation period, defined as the dates between the first and last influenza positive research enrollment during each season, was determined for each year in both the administrative and research databases. The respiratory viral panels (RVPs) were performed on a nasopharyngeal swab. RVP tests might be conducted year-round, but were more routinely conducted in October through April on patients presenting with acute respiratory symptoms. For patients with more than one visit with RVP tests less than 14 days apart, only data from the first visit were included. If visits occurred greater than 14 days apart, then data from both visits were included. For patients with more than one visit with tests less than 14 days apart, only data from the first visit were included. If visits occurred greater than 14 days apart, then data from both visits were included]. The case was considered as suspected vaccination failure being time to onset unknown. The case was considered as serious due to suspected vaccination failure. Treatment was unknown. Outcome was not reported. The authors commented "In this comparison of influenza vaccine effectiveness estimates from a test-negative case-control research study and administrative data sources, subjects differed by demographic characteristics of age, race and site of enrollment. The administrative database included older patients, more non-whites and more patients enrolled in the emergency department. In emergency departments, research enrollees were younger, more often male and non-white, and VE against any influenza and all influenza A was significantly higher than was found in the administrative database. Whereas, in the outpatient clinics, age distribution was more evenly distributed in the administrative database and vaccination rates appeared to be higher than in the research database, but there were no significant differences in VE estimates. These differences may be attributed to the fact that recruitment for this research study was limited to two emergency departments (one a pediatric hospital) among several included in the administrative database and to a greater emphasis on research enrollment at urgent and primary care centers". The authors concluded "The selection of the appropriate method for determining influenza vaccine effectiveness depends on a multitude of factors. Among those factors is sample size, which likely obscured significant differences between administrative and research database VE estimates in this study except when limiting the analyses to the emergency departments. In this case, the research estimates were better. Differences in the types of persons enrolled in the databases, suggest that research estimates may be more generalizable. Other advantages of research databases for VE estimates include lack of clinician-related selection bias for testing and less misclassification of vaccination status because multiple sources are used. The advantages of the administrative databases are potentially shorter time to VE results and lower cost.".  MAH Comment: No reasonable causal relationship based on vaccination failure, influenza b virus infection, acute respiratory tract infection and cough due to insufficient information for Flu Seasonal QIV Dresden.