A Study to Learn How Paxlovid [Nirmatrelvir-ritonavir/PF-07321332] Works in COVID-19 Patients Who Are Elderly or Have Medical Conditions.

December 2, 2025 updated by: Pfizer

A Real-world Study on the Effectiveness of Nirmatrelvir-ritonavir in Reducing Severe Outcomes From COVID-19

The purpose of this study is to learn about the effects of the study medicine called Paxlovid [nirmatrelvir-ritonavir/PF-07321332], for the potential treatment of COVID-19.

This study will use patient health records in Ontario, to find people who were sick with COVID-19 and visited a pharmacist to be treated, anytime from December 1st, 2022, to March 31st, 2024. To be included in our study, the people must be over 18 years of age and be registered in the Ontario health system for at least one year. People were not included in our study if they have been pregnant in the past year or have serious kidney or liver disease.

We will separate the people in the study into two groups: those who received treatment with Paxlovid [nirmatrelvir-ritonavir/PF-07321332] and those who received no treatment. We will monitor their healthcare visits or if they die for any reason, for up to 60 days after the date that they visited their pharmacist. Then we will compare participant experiences when they are taking the study medicine to when they are not. This will help us determine if the study medicine is effective.

Study Overview

Status

Active, not recruiting

Conditions

Intervention / Treatment

Study Type

Observational

Enrollment (Actual)

99000

Contacts and Locations

This section provides the contact details for those conducting the study, and information on where this study is being conducted.

Study Locations

  • United States
    • New York
      • New York, New York, United States, 10001
        • Pfizer New York

Participation Criteria

Researchers look for people who fit a certain description, called eligibility criteria. Some examples of these criteria are a person's general health condition or prior treatments.

Eligibility Criteria

Ages Eligible for Study

  • Adult
  • Older Adult

Accepts Healthy Volunteers

No

Sampling Method

Non-Probability Sample

Study Population

The Institute for Clinical Evaluative Sciences (ICES) data repository consists of de-identified, record-level, coded and linkable health data sets. It encompasses much of the publicly funded administrative health services records for the Ontario population eligible for universal health coverage since 1986 and integrates administrative data, registries, and surveys.

Description

Inclusion

  • Record of at least 1 nirmatrelvir-ritonavir prescription and at least 1 dispensation issued by the pharmacist (Treated Cohort only) within 5 days of prescription, identified through pharmacy billing codes
  • Record of at least 1 assessment for nirmatrelvir-ritonavir, without a prescription issued by the pharmacist (Untreated Cohort only), OR record of at least 1 prescription for nirmatrelvir-ritonavir without dispensation (Untreated Cohort only), identified through pharmacy billing codes

Exclusion

  • Invalid or incomplete records (e.g., missing age, missing sex, death before index)
  • Record of a positive PCR test for SARS-CoV-2 between 5 and 90 days prior to the index date
  • Had a prescription for antivirals within 3 days prior to or on the index date

Study Plan

This section provides details of the study plan, including how the study is designed and what the study is measuring.

How is the study designed?

Design Details

Cohorts and Interventions

Group / Cohort
Intervention / Treatment
Assessed and Treated Cohort
Participants who were assessed with Covid prescribed and subsequently dispensed nirmatrelvir-ritonavir during the selection period
Drug: nirmatrelvir-ritonavir
Participants who were assessed with Covid prescribed and subsequently dispensed nirmatrelvir-ritonavir during the selection period
Other Names:
  • paxlovid
Assessed and Untreated Cohort
Participants who were assessed with Covid for nirmatrelvir-ritonavir but either were not prescribed the medication or did not have it dispensed during the selection period
Other: No treatment
Participants who were assessed with Covid for nirmatrelvir-ritonavir but either were not prescribed the medication or did not have it dispensed during the selection period

What is the study measuring?

Primary Outcome Measures

Outcome Measure
Time Frame
Time to the first severe composite outcome (all-cause hospital admission, ICU admission, or death) within 30 days of treatment assessment.
Time Frame: Participants selected between 01 Dec, 2022 to 31 March 2024
Participants selected between 01 Dec, 2022 to 31 March 2024

Secondary Outcome Measures

Outcome Measure
Time Frame
Time to the first severe composite outcome (all-cause hospital admission, ICU admission, or death) within 60 days of treatment assessment.
Time Frame: Participants selected between 01 Dec, 2022 to 31 March 2024
Participants selected between 01 Dec, 2022 to 31 March 2024

Collaborators and Investigators

This is where you will find people and organizations involved with this study.

Sponsor

Pfizer

Investigators

  • Study Director: Pfizer CT.gov Call Center, Pfizer

Publications and helpful links

The person responsible for entering information about the study voluntarily provides these publications. These may be about anything related to the study.

Helpful Links

Study record dates

These dates track the progress of study record and summary results submissions to ClinicalTrials.gov. Study records and reported results are reviewed by the National Library of Medicine (NLM) to make sure they meet specific quality control standards before being posted on the public website.

Study Major Dates

Study Start (Actual)

October 27, 2025

Primary Completion (Estimated)

March 30, 2026

Study Completion (Estimated)

March 30, 2026

Study Registration Dates

First Submitted

November 21, 2025

First Submitted That Met QC Criteria

November 21, 2025

First Posted (Estimated)

December 3, 2025

Study Record Updates

Last Update Posted (Estimated)

December 4, 2025

Last Update Submitted That Met QC Criteria

December 2, 2025

Last Verified

December 1, 2025

More Information

Terms related to this study

Keywords

Additional Relevant MeSH Terms

Other Study ID Numbers

  • C4671071

Plan for Individual participant data (IPD)

Plan to Share Individual Participant Data (IPD)?

NO

IPD Plan Description

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.

Drug and device information, study documents

Studies a U.S. FDA-regulated drug product

Yes

Studies a U.S. FDA-regulated device product

No

This information was retrieved directly from the website clinicaltrials.gov without any changes. If you have any requests to change, remove or update your study details, please contact register@clinicaltrials.gov. As soon as a change is implemented on clinicaltrials.gov, this will be updated automatically on our website as well.

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