The goal of this study is to assess serious adverse events associated with hospitalizations in the non-acute phase after vaccination with the mRNA-1273 vaccine in persons with underlying diseases who are considered to have a high risk of severe exacerbation of COVID-19.

Data collected from the JMDC Claims database from May 2020 to October 2022.

Inclusion Criteria:

• Participants registered to receive the mRNA-1273 vaccine in the Pep Up vaccination history Database
• Participants who have a history of vaccination with the mRNA-1273 vaccine in the Pep-Up vaccination history Database and the observation start date is at least 6 months prior to vaccination with the mRNA-1273 vaccine and have underlying diseases.

Exclusion Criteria:

• Underlying diseases that were determined undetectable by the pre-screening of JMDC
• Participants who did not consent to the questionnaire.

The study population was selected from participants who were registered to receive the mRNA-1273 vaccine in the Pep Up vaccination history Database whose start date of observation in the claim database was within 6 months or more before vaccination with mRNA-1273 vaccine, and those who met the definition of underlying disease based on the claim data for 6 months.