The goal of this study is to confirm the onset status of hypersensitivity reactions including shock and anaphylaxis observed after vaccination with this drug in persons with underlying diseases who are considered to have a high risk of severe exacerbation of COVID-19 and explore risk factors.

Data collected from the JDMC Claims Database between May 2021 to November 2021.

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. Data period for confirmation of presence/absence of underlying disease is May 2021 to November 2021.

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.