This is a cohort study that will include Paxlovid (nirmatrelvir-ritonavir) treatment eligible for people with a positive SARS-CoV-2 diagnostic test and at least one COVID-19 symptom. This study will look at the change in Post Covid Conditions measured by the number of outpatients, Emergency department, urgent care and inpatient visits before and after COVID-19 between those who did and did not receive Paxlovid. In addition, changes in frailty post-acute infection will be evaluated, in a separate analysis. It is hypothesized that individuals with COVID-19 who received Paxlovid will have a smaller post-COVID-19 increase (vs pre-COVID) in PCC healthcare utilization (i.e., cardiopulmonary) in comparison to patients with COVID-19 who did not receive Paxlovid.

Inclusion Criteria:

• Developed at least one COVID-19 symptom between Apr 1, 2022 through Dec 31, 2023
• A positive lab-confirmed polymerase chain reaction (PCR) SARS-COV-2 test 5 days after symptom onset (primary analysis).
• Continuous enrollment in KPSC health plans for at least 1 year (allowing for a 31-day gap to account for potential delays in membership renewal) before the date of symptom onset
• Active membership in KPSC health plans for at least 31 days after the date of symptom onset
• Eligible for nirmatrelvir-ritonavir defined by age and CDC-defined risk factors for severe COVID-19

Exclusion Criteria:

• Individuals on another medication that is contraindicated for treatment with nirmatrelvir-ritonavir defined as having any prescription drug claim in the 90 days prior to COVID-19 symptom onset
• Receipt of any COVID-19 antiviral (molnupiravir, remdesivir, nirmatrelvir/ritonavir) or monoclonal antibody treatment (bamlanivimab, bebtelovimab, casirivimab/imdevimab, cilgavimab/tixagevimab, otrovimab,) <180 days prior to COVID-19 symptom onset
• Any positive SARS-CoV-2 test, including self-reported tests, <180 days prior to COVID-19 symptom onset.

Members of the Kaiser Permanente Southern California integrated healthcare delivery system.

Pfizer will provide access to individual de-identified participant data and related study documents (e.g. protocol, Statistical Analysis Plan (SAP), Clinical Study Report (CSR)) upon request from qualified researchers, and subject to certain criteria, conditions, and exceptions. Further details on Pfizer's data sharing criteria and process for requesting access can be found at: https://www.pfizer.com/science/clinical\_trials/trial\_data\_and\_results/data\_requests.