Appendicitis; This literature-non-study case was reported in a literature article and describes the occurrence of APPENDICITIS (Appendicitis) in a  patient of an unknown age and gender who received mRNA-1273 (Spikevax) for COVID-19 prophylaxis.       No Medical History information was reported.    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 APPENDICITIS (Appendicitis) (seriousness criterion medically significant). At the time of the report, APPENDICITIS (Appendicitis) outcome was unknown.        For mRNA-1273 (Spikevax) (Unknown), the reporter did not provide any causality assessments.   This report concerns patient who experienced Appendicitis after second dose of Moderna. Concomitant and treatment medications were not reported.  This study described simultaneous vaccination (SV) with primary series COVID-19 vaccines and assess 23 pre-specified health outcomes following SV among persons aged =5 years in the Vaccine Safety Datalink (VSD).  This study utilized VSD's COVID-19 vaccine surveillance data from December 11, 2020-May 21, 2022. Analyses assessed frequency of SV.   Rate ratios (RRs) were estimated by Poisson regression when the number of outcomes was =5 across both doses, comparing outcome rates between COVID-19 vaccinees receiving SV and COVID-19 vaccinees receiving no SV in the 1-21 days following COVID-19 vaccine dose 1 and 1-42 days following dose 2 by SV type received ("All SV", "Influenza SV", "Non-influenza SV").  The most frequent simultaneous vaccines were influenza, HPV, Tdap, and meningococcal. Outcomes following SV with COVID-19 vaccines were rare (total of 56 outcomes observed after dose 1 and dose 2).   Adjusted RRs for the All Simultaneous Vaccines" group were statistically significantly elevated for appendicitis in the 121 days following COVID-19 vaccine dose 1. Of the nine appendicitis cases, one patient received Moderna COVID-19 vaccine.  Authors concluded that overall, the combined pre-specified health outcomes observed among persons who received simultaneous vaccines with COVID-19 vaccine were also rare and not at a statistically significantly different rate compared with those who did not receive simultaneous vaccination with the COVID-19 vaccine. Statistically significant adjusted rate ratios were observed for some individual outcomes (appendicitis, convulsions/seizures, and Bell's palsy), but the number of cases was small, there was no adjustment for multiple testing, and the possible effect of residual unmeasured confounding in these analyses may have contributed to these findings.  Company Comment: This is a Literature-Non-Study case concerning a patient with no reported  age, gender, nor medical history, who experienced the unexpected serious (medically significant) AESI of Appendicitis. The event occurred between 1-42 days after the administration of the second dose of mRNA-1273 vaccine, however exact latency could not be assessed due to lack of information.  No further information on clinical course, investigations and treatment received was available in the report. More information is requested. The benefit-risk relationship of mRNA-1273 Vaccine is not affected by this report.   This case was linked to US-MODERNATX, INC.-MOD-2023-731103 (Linked Report).; Sender's Comments:  US-MODERNATX, INC.-MOD-2023-731103:First Dose (Master Case)