This case was reported in a literature article and described the occurrence of vaccination failure in a 7-year-old male patient who received Flu unspecified (Influenza vaccine) for prophylaxis. On an unknown date, the patient received Influenza vaccine at an unknown dose. On an unknown date, unknown after receiving Influenza vaccine, the patient experienced vaccination failure (serious criteria hospitalization and GSK medically significant), influenza a virus infection (serious criteria hospitalization), viral parotitis (serious criteria hospitalization), neck swelling (serious criteria hospitalization), fatigue (serious criteria hospitalization), cough (serious criteria hospitalization), respiratory tract congestion (serious criteria hospitalization), rhinorrhea (serious criteria hospitalization), feeling hot (serious criteria hospitalization), neck edema (serious criteria hospitalization), red neck (serious criteria hospitalization), lymphadenopathy cervical (serious criteria hospitalization) and facial swelling (serious criteria hospitalization). The patient was treated with Corticosteroids (Drug Name Unknown), Antibiotics (Brand Names Not Known) and antitussives, excl combinations with expector (Antitussives). On an unknown date, the outcome of the vaccination failure, influenza a virus infection, viral parotitis, neck swelling, fatigue, respiratory tract congestion, cough, rhinorrhea, feeling hot, neck edema, red neck, lymphadenopathy cervical and facial swelling were recovering/resolving. The reporter considered the vaccination failure, influenza a virus infection, viral parotitis, neck swelling, fatigue, cough, respiratory tract congestion, rhinorrhea, feeling hot, neck edema, red neck, lymphadenopathy cervical and facial swelling to be related to Influenza vaccine. Lab Comments: Lab tests were performed on unspecified dates. The patient was previously evaluated at an outside hospital (determined influenza negative at that time). Physical examination revealed a bilateral swollen edematous and erythematous neck (right greater than left) with anterior chain cervical lymphadenopathy. The neck was supple and tender (range-of-motion preserved), with gross swelling of submandibular soft tissue. Imaging was then performed, with neck ultrasound and radiograph revealing enlarged bilateral submandibular and parotid glands. Prominent vascularity of the parotid glands was noted on Doppler imaging. The patient was diagnosed with virally induced parotitis and submandibular swelling secondary to influenza A. Neck radiograph anterio-posterior (AP) view showed swelling involving the parotid and submandibular glands more pronounced on the right side and lateral neck radiograph shows extensive, submental, neck swelling, with normal airway and epiglottis. No prevertebral soft tissue swelling was evident. Vertebral bodies and intervertebral disk spaces were preserved. There was no airway abnormality noted. The radiographic appearance, without thorough history provided (extensive submandibular swelling), was most immediately concerning for Ludwig's Angina, and the recommendation for follow-up imaging (compute tomography (CT) with contrast) was made at that time. Instead, neck ultrasonography was obtained. Neck ultrasound (performed 1 hour later) showed edematous subcutaneous tissues present within the bilateral neck and several scattered borderline enlarged cervical lymph nodes (right 0.8 × 0.9 × 0.5 cm and left 2.3 × 1.5 × 0.6 cm). Significant enlargement of bilateral parotid glands (right greater than left) was noted, along with mild enlargement of bilateral submandibular glands. Color Doppler revealed hypervascularity of the parotid glands bilaterally, with a hyperechoic area observed on the left side (2.6 × 2.7 × 1.6 cm also hypervascular, not shown).