Suspected vaccination failure; Influenza virus infection; retropharyngeal abscess; Peritonsillar abscess; Streptococcus pyogenes/bacterial head and neck infections; with polymicrobial infection with Prevotella; This case was reported in a literature article and described the occurrence of suspected vaccination failure in a 13-year-old male patient who received Flu unspecified (Flu vaccine) for prophylaxis.  Co-suspect products included PNEUMOCOCCAL VACCINE (PNEUMOCOCCAL 7-VALENT CONJUGATE VACCINE) for prophylaxis.   Previously administered products included influenza vaccine (in 2006, 2007, 2009, 2012, 2014 and 2015.) and PNEUMOCOCCAL 7-VALENT CONJUGATE VACCINE (1st 3 doses received on unknown date).   On an unknown date, the patient received Flu vaccine at an unknown dose and the 4th dose of PNEUMOCOCCAL 7-VALENT CONJUGATE VACCINE. On an unknown date, less than a year after receiving Flu vaccine, the patient experienced vaccination failure (serious criteria hospitalization and GSK medically significant), influenza (serious criteria hospitalization), retropharyngeal abscess (serious criteria hospitalization and GSK medically significant), peritonsillar abscess (serious criteria hospitalization and GSK medically significant), streptococcal infection (serious criteria hospitalization and GSK medically significant) and bacterial infection (serious criteria hospitalization). The subject was treated with benzylpenicillin (Penicillin). On an unknown date, the outcome of the vaccination failure was unknown and the outcome of the influenza, retropharyngeal abscess, peritonsillar abscess, streptococcal infection and bacterial infection were recovering/resolving.   The reporter considered the vaccination failure, influenza, retropharyngeal abscess, peritonsillar abscess, streptococcal infection and bacterial infection to be related to Flu vaccine.  Additional details were reported as follows: This case was reported in a literature article and described the suspected vaccination failure in a 13.9-year-old male patient, who was vaccinated with unspecified 2017-2018 seasonal influenza vaccine (manufacturer unknown) for prophylaxis. This case corresponds to case-5 from table 1 reported in this literature article. The patient was a part of retrospective review that was performed for pediatric patients hospitalized with bacterial head or neck infections following influenza infection between October 2017 and March 2018.The patient had received influenza vaccine previously in 2006, 2007, 2009, 2012, 2014 and 2015. No information on patient's medical history, family history or concurrent condition or concomitant medication was provided. On an unspecified date in 2017, the patient received unspecified 2017-2018 seasonal influenza vaccine (administration route and site unspecified, dosage unknown; batch number not provided). The patient had also received 4 doses of unspecified 7-valent pneumococcal conjugate vaccine (PCV7). The age of vaccinations was not provided.  On an unspecified date, an unknown period after the seasonal influenza vaccination, the patient developed influenza virus infection that was subsequently diagnosed with positive rapid influenza diagnostic test. The type of influenza virus was unknown. On an unspecified date between October 2017 and March 2018, at the age of 13.9 years, 6 days after the influenza diagnosis, the patient was hospitalised for retropharyngeal abscess (RPA) and peritonsillar abscess (bacterial head or neck infections which were associated with influenza infection).  The incision and drainage was performed. The causative pathogen for head or neck infection was found to be Streptococcus pyogenes. The patient was also found positive with polymicrobial infection with Prevotella. The duration of hospitalization was between 5 and 35 days. The treatment was started with penicillin (definitive treatment). The duration of treatment was 3 weeks. The patient had completed penicillin treatment successfully and had favorable outcome. This case has been considered as suspected vaccination failure being the time to onset was unknown. This case has been considered as serious due to suspected vaccination failure/hospitalisation. The author did not comment on the relationship between the event of influenza virus infection, and unspecified seasonal influenza vaccine. However the authors stated, "Seasonal influenza infection is associated with secondary bacterial complications involving the upper and lower respiratory tract. However, the association of influenza infection with secondary severe or complicated head and neck infections is not appreciated." The authors concluded, "It was suggested that complicated bacterial head and neck infections may represent an under recognized co-infection or secondary complication of infection with influenza virus, further stressing the importance of prevention and treatment of influenza infection." This article corresponding to this case is not available for regulatory submission due to copyright restriction. This is 1 of the 2 valid cases reported in this literature article.      Lab Comments: On an unspecified date between October 2017 and March 2018,  lab test were performed.