The trial prematurely terminated due to the inability to recruit the planned number of subjects. The decision to terminate the trial was not based on any safety concerns.

The purpose of this clinical trial is to learn about how study medicine (Paxlovid, which contains nirmatrelvir and ritonavir) is changed and eliminated from the body, as well as its safety, and the extent to which side effects can be tolerated for treatment of pregnant women with mild or moderate COVID-19 compared to non-pregnant women with mild or moderate COVID-19.

This study is seeking participants who:

• are expecting a healthy baby and are in their second or third trimester pregnancy and have mild or moderate COVID-19
• are not pregnant and have mild or moderate COVID-19.

All participants in this study will take Paxlovid by mouth every 12 hours for 5 days. We will study the experiences of people receiving the study medicine. This will help us decide if the study medicine is safe.

All participants will take part in this study for at least 34 days; pregnant participants will take part until their delivery, so that the study duration may be up to 6 months, depending on their delivery date.

During this time, participants will have 7to 8 visits and, if pregnant, a visit at delivery. Around 2 to 3 visits and the delivery visit will be done in person (at the clinic or at the participant's home). The other 5 visits may be done over the phone, unless in-person visit is necessary as decided by the doctor. Blood samples will be collected on the first 4 to 5 study visits (and at other study visits, if necessary).

Inclusion Criteria:

• All cohorts: Mild-to-moderate COVID-19 infection confirmed in sample collected ≤5 days prior to enrollment; onset within 5 days prior to enrollment and presence of ≥1 sign/symptom on the day of enrollment.
• Cohorts 1&2: Expecting single baby; Pregnant in 2nd trimester, 14 0/7 to 27 6/7 weeks of gestational age (Cohort 1) or 3rd trimester, ≥28 0/7 and ≤34 6/7 weeks of gestational age (Cohort 2), by ultrasound.
• All cohorts: Otherwise healthy participants who are determined by medical history, physical examination, and clinical judgment to be appropriate for inclusion in the study

Exclusion Criteria:

• All cohorts: Current need for hospitalization or anticipated need for hospitalization in the clinical opinion of the site investigator.
• Cohorts 1&2: Prior/current major condition or illness of mother/fetus substantially increasing risk of study participation/completion or impacting pregnancy/fetal outcomes in investigator's judgement.
• All cohorts: Current use of any medications that are highly dependent on CYP3A4 for clearance, and which are contraindicated in combination with nirmatrelvir/ritonavir.
• All cohorts: Has received or is expected to receive monoclonal antibody treatment, convalescent COVID-19 plasma, or anti-viral treatment (eg, molnupiravir) for the current SARSCoV-2 infection.
• All cohorts: Participants with moderate to severe kidney impairment

Pregnant and non-pregnant females

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.

(Open Label)