anti-PL12 positive antisynthetase syndrome (ASS); This literature-non-study case was reported in a literature article and describes the occurrence of ANTISYNTHETASE SYNDROME (anti-PL12 positive antisynthetase syndrome (ASS)) in a 31-year-old male patient who received mRNA-1273 (Spikevax) for COVID-19 prophylaxis.    The patient's past medical history included Non-smoker. Concurrent medical conditions included Morbid obesity, Obstructive sleep apnea syndrome and Type 1 diabetes mellitus.   On an unknown date, the patient received second dose of mRNA-1273 (Spikevax) (unknown route) 1 dosage form. On an unknown date, the patient experienced ANTISYNTHETASE SYNDROME (anti-PL12 positive antisynthetase syndrome (ASS)) (seriousness criterion hospitalization). The patient was treated with CEFTRIAXONE at an unspecified dose and frequency; AZITHROMYCIN at an unspecified dose and frequency and AZATHIOPRINE at an unspecified dose and frequency. At the time of the report, ANTISYNTHETASE SYNDROME (anti-PL12 positive antisynthetase syndrome (ASS)) was resolving.      DIAGNOSTIC RESULTS (normal ranges are provided in parenthesis if available): On an unknown date, Antinuclear antibody: (Positive) Positive. On an unknown date, Bronchoalveolar lavage: (Negative) It was negative for viral, bacterial, fungal, mycobacterial, Pneumocystis jiroveci.. On an unknown date, C-reactive protein: 153.7 milligram per millilitre 153.7 mg/ml. On an unknown date, Computerised tomogram thorax: It showed bibasilar lung infiltrates., It showed multiple bilateral moderate pulmonary emboli (PE) and persistent lung infiltrates. and It showed resolution of PE but revealed persistent bibasilar infiltrates, worsening consolidation at the bases and a new pneumomediastinum. On an unknown date, Full blood count: It was unremarkable. On an unknown date, Heart rate: 107 107 beats/min. On an unknown date, Laboratory test: It was unremarkable. On an unknown date, Oxygen saturation: 10 liter and 93 %. On an unknown date, Physical examination: It was significant for diminished breath sounds bilaterally.. On an unknown date, Red blood cell sedimentation rate: 61 mm/hr. On an unknown date, SARS-CoV-2 test: (Negative) Negative.   For mRNA-1273 (Spikevax) (Unknown), the reporter considered ANTISYNTHETASE SYNDROME (anti-PL12 positive antisynthetase syndrome (ASS)) to be related.    No concomitant medication was reported.  Patient experienced symptoms like progressive dyspnea, chest tightness and mildly productive cough of 1-month duration, ILD without myositis and was presented to the emergency department. Patient was treated with unspecified steroids and anticoagulants. Patient was initiated with a high dose steroid with significant improvement in symptoms along with oxygen requirements and imaging. Extensive infectious disease workup for bacterial, fungal and viral pathogens was negative except for Mycoplasma IgG. Hypersensitivity pneumonitis testing for fungal, bacterial and pigeon serum was also unremarkable. Autoimmune testing was weakly positive for Anti-Nuclear Antibodies and the presence of SSA/Ro IgG antibody. Anti-PL-12 antibody resulted positive with normal creatine kinase. Hypoxia remained leading to elective intubation with bronchoscopy  Company Comment: This is a literature-non-study case concerning a 31-year-old, male patient with no relevant medical history. Patient has no reported vaccination history. Patient experienced the unexpected serious (hospitalization) event of antisynthetase syndrome (anti-PL12 positive antisynthetase syndrome (ASS)). The event occurred after the second dose of mRNA-1273 vaccine administration. The event was described as, patient presented to the emergency department with progressive dyspnea, chest tightness and mildly productive cough of 1-month duration. Patient's vitals were remarkable for tachycardia of 107 beats/min and SaO2 93% on 10L oxygen. Physical examination was significant for diminished breath sounds bilaterally. Complete blood count and chemistry panel were unremarkable. Erythrocyte Sedimentation Rate: 61 mm/hr (elevated) and C-Reactive Protein 153.7 mg/ml (elevated). Computed tomography (CT) of the chest revealed bibasilar lung infiltrates. Patient was empirically started on Ceftriaxone and Azithromycin. Extensive infectious disease workup for bacterial, fungal and viral pathogens was negative except for Mycoplasma IgG. Hypersensitivity pneumonitis testing for fungal, bacterial, and pigeon serum was also unremarkable. Autoimmune testing was weakly positive for Anti-Nuclear Antibodies (1:40) and the presence of SSA/Ro IgG antibody. With worsening hypoxia, repeat CT chest with an angiogram (CTA) revealed multiple bilateral moderate pulmonary emboli (PE) and persistent lung infiltrates. Treatment with steroids and anticoagulants was initiated. However, patient's hypoxia remained, leading to elective intubation with bronchoscopy. Bronchoalveolar lavage for viral, bacterial, fungal, mycobacterial, Pneumocystis jiroveci and repeat Covid-19 testing came back negative. Repeat CTA showed resolution of PE but revealed persistent bibasilar infiltrates, worsening consolidation at the bases and a new pneumomediastinum. Myopathic markers were sent due to SSA/Ro IgG antibody positivity. Anti-PL-12 antibody resulted positive with normal creatine kinase. Rheumatology was consulted and a high dose steroid taper with Azathioprine was initiated with significant improvement in symptoms, oxygen requirements and imaging. Patient was diagnose with ASS without associated myositis. No other information surrounding the event was reported. The outcome of the event was resolving. The benefit-risk relationship of mRNA-1273 vaccine is not affected by this report.; Sender's Comments: This is a literature-non-study case concerning a 31-year-old, male patient with no relevant medical history. Patient has no reported vaccination history. Patient experienced the unexpected serious (hospitalization) event of antisynthetase syndrome (anti-PL12 positive antisynthetase syndrome (ASS)). The event occurred after the second dose of mRNA-1273 vaccine administration. The event was described as, patient presented to the emergency department with progressive dyspnea, chest tightness and mildly productive cough of 1-month duration. Patient's vitals were remarkable for tachycardia of 107 beats/min and SaO2 93% on 10L oxygen. Physical examination was significant for diminished breath sounds bilaterally. Complete blood count and chemistry panel were unremarkable. Erythrocyte Sedimentation Rate: 61 mm/hr (elevated) and C-Reactive Protein 153.7 mg/ml (elevated). Computed tomography (CT) of the chest revealed bibasilar lung infiltrates. Patient was empirically started on Ceftriaxone and Azithromycin. Extensive infectious disease workup for bacterial, fungal and viral pathogens was negative except for Mycoplasma IgG. Hypersensitivity pneumonitis testing for fungal, bacterial, and pigeon serum was also unremarkable. Autoimmune testing was weakly positive for Anti-Nuclear Antibodies (1:40) and the presence of SSA/Ro IgG antibody. With worsening hypoxia, repeat CT chest with an angiogram (CTA) revealed multiple bilateral moderate pulmonary emboli (PE) and persistent lung infiltrates. Treatment with steroids and anticoagulants was initiated. However, patient's hypoxia remained, leading to elective intubation with bronchoscopy. Bronchoalveolar lavage for viral, bacterial, fungal, mycobacterial, Pneumocystis jiroveci and repeat Covid-19 testing came back negative. Repeat CTA showed resolution of PE but revealed persistent bibasilar infiltrates, worsening consolidation at the bases and a new pneumomediastinum. Myopathic markers were sent due to SSA/Ro IgG antibody positivity. Anti-PL-12 antibody resulted positive with normal creatine kinase. Rheumatology was consulted and a high dose steroid taper with Azathioprine was initiated with significant improvement in symptoms, oxygen requirements and imaging. Patient was diagnose with ASS without associated myositis. No other information surrounding the event was reported. The outcome of the event was resolving. The benefit-risk relationship of mRNA-1273 vaccine is not affected by this report.