Dr. Kitajima et al reply.

We thank Mutoh et al1 for their interest in our study on antimelanoma differentiation-associated gene 5 antibody-positive interstitial lung disease (anti-MDA5-ILD) after vaccination with coronavirus disease 2019 (COVID-19) mRNA vaccines2 and for sharing their clinical experience. Mutoh et al1 reported a case of anti-MDA5-ILD that developed 8 weeks after COVID-19 mRNA vaccination in Japan.

Antimelanoma Differentiation-Associated Gene 5 Antibody-Positive Interstitial Lung Disease After Vaccination With COVID-19 mRNA Vaccines.

OBJECTIVE: Melanoma differentiation-associated gene 5 (MDA5) is a viral RNA sensor induced by SARS-CoV-2. Similarities have been reported between the clinical presentations of coronavirus disease 2019 (COVID-19) pneumonia and anti-MDA5 antibody-positive interstitial lung disease (anti-MDA5-ILD). However, it is unknown whether COVID-19 mRNA vaccines are associated with anti-MDA5-ILD. METHODS: We retrospectively reviewed consecutive patients with anti-MDA5-ILD admitted to our hospital between April 2017 and March 2022. In addition, we investigated the clinical presentations of patients who developed anti-MDA5-ILD after vaccination with COVID-19 mRNA vaccines. We also examined the annual number of anti-MDA5-ILD cases before and after the COVID-19 vaccination campaign. RESULTS: Nine patients with anti-MDA5-ILD were seen during the study period, of whom 4 developed anti-MDA5-ILD between August and October 2021, approximately 6 to 12 weeks after vaccination with a COVID-19 mRNA vaccine and a few months after the rapid mRNA COVID-19 vaccination campaign in Japan. None of the 4 patients had evidence of SARS-CoV-2 infection. The difference in the annual number of anti-MDA5-ILD cases before vs after the COVID-19 vaccination campaign (1.25 ± 0.96 cases/yr vs 4.0 cases/yr) was not statistically significant (P = 0.08). CONCLUSION: We encountered 4 cases of anti-MDA5-ILD after COVID-19 vaccination. Further large population studies are needed to clarify the relationship between anti-MDA5-ILD and vaccination with COVID-19 mRNA vaccines.

Pneumonia Caused by Severe Acute Respiratory Syndrome Coronavirus 2 and Influenza Virus: A Multicenter Comparative Study.

BACKGROUND: Detailed differences in clinical information between severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) pneumonia (CP), which is the main phenotype of SARS-CoV-2 disease, and influenza pneumonia (IP) are still unclear. METHODS: A prospective, multicenter cohort study was conducted by including patients with CP who were hospitalized between January and June 2020 and a retrospective cohort of patients with IP hospitalized from 2009 to 2020. We compared the clinical presentations and studied the prognostic factors of CP and IP. RESULTS: Compared with the IP group (n = 66), in the multivariate analysis, the CP group (n = 362) had a lower percentage of patients with underlying asthma or chronic obstructive pulmonary disease (P < .01), lower neutrophil-to-lymphocyte ratio (P < .01), lower systolic blood pressure (P < .01), higher diastolic blood pressure (P < .01), lower aspartate aminotransferase level (P < .05), higher serum sodium level (P < .05), and more frequent multilobar infiltrates (P < .05). The diagnostic scoring system based on these findings showed excellent differentiation between CP and IP (area under the receiver operating characteristic curve, 0.889). Moreover, the prognostic predictors were different between CP and IP. CONCLUSIONS: Comprehensive differences between CP and IP were revealed, highlighting the need for early differentiation between these 2 pneumonias in clinical settings.