Demographic characteristics for the modified intention-to-treat (mITT) 1 analysis set were similar between the nirmatrelvir/ritonavir and placebo groups.
Over half of participants were female and the majority were White. Approximately 41% of participants were Hispanic or Latino.
The median age was 41 (range: 18, 87) years and nearly 90% of participants were under 60 years of age at the time of randomization. The mean (standard deviation [SD]) body mass index (BMI) was 26.26 (5.15) kg/m2, and approximately 49% of participants had a BMI >=25 kg/m2 at the time of screening.
Baseline characteristics were balanced between both treatment groups.
Based on the 4 site exclusions due to GCP noncompliance or data anomalies, the number of participants analyzed per analysis population was: full analysis set, 1296; safety analysis set, 1288; mITT1, 1288; mITT, 929; and per protocol analysis set, 1218.
The proportion of participants who completed each phase of the study was similar for both treatment groups.
* During the treatment phase, the most common reason for discontinuation of study intervention was adverse event (AE) and withdrawal by subject. None of the 21 participants who discontinued study intervention during the treatment phase due to an AE discontinued the study.
* During the follow-up phase, the most frequent reason for study discontinuation was withdrawal by subject.
* The most frequent reason for study discontinuation during the long-term follow-up phase was study terminated early by the sponsor due to the low rate of hospitalization or death.
The proportion of participants with all-causality treatment-emergent adverse events (TEAEs) that started on or prior to the Day 34 visit was comparable between the nirmatrelvir/ritonavir (25.8%) and placebo (24.1%) groups.
Most of the all-causality TEAEs experienced by participants in both treatment groups were mild (Grade 1) to moderate (Grade 2) in severity. The proportion of participants with all-causality severe (Grade 3) or potentially life threatening (Grade 4) TEAEs was comparable between the nirmatrelvir/ritonavir (3.7%) and placebo (3.9%) groups.
Of the most frequently reported all-causality TEAEs (>=1%), the following were reported at a higher frequency (>=3 participant difference) in the nirmatrelvir/ritonavir group compared with the placebo group: Dysgeusia (6.7% vs 0.5%, respectively), Diarrhoea (4.0% vs 3.0%, respectively), Dyspepsia (1.2% vs 0.3%, respectively), Nausea (3.1% vs 2.7%, respectively), Alanine aminotransferase (ALT) increased (2.1% vs 1.3%, respectively), and Aspartate aminotransferase (AST) increased (1.4% vs 0.6%, respectively).
* In the nirmatrelvir/ritonavir group, these TEAEs were nonserious and mostly mild (Grade 1) or moderate (Grade 2) in severity.
* Of these TEAEs, discontinuation of nirmatrelvir/ritonavir occurred in 3 participants for Dysgeusia, 2 participants each for Diarrhoea and Dyspepsia, and 1 participant for Nausea.
The proportion of participants with all-causality treatment-emergent serious adverse events (SAEs) was low and comparable between the nirmatrelvir/ritonavir (1.2%) and placebo (1.9%) groups. The most frequently reported all-causality SAEs (>=2 participants) in the nirmatrelvir/ritonavir and placebo groups were coronavirus disease 2019 (COVID-19) pneumonia (0.5% and 1.3%, respectively) and Pneumonia (0.2% and 0.3%, respectively). No SAEs were considered treatment-related by the investigator.
Hemodynamic and inflammatory adverse events of special interest (AESIs) reported at a greater frequency (>=2 participant difference) in the nirmatrelvir/ritonavir group compared with the placebo group were: Syncope (3 [0.5%] vs 0 participants, respectively), Hypotension (2 [0.3%] vs 0 participants, respectively), and Prothrombin time prolonged (3 [0.5%] vs 1 [0.2%] participants, respectively). No thyroid-related AESIs were reported at a greater frequency (>=2 participant difference) in the nirmatrelvir/ritonavir group compared with the placebo group. AESIs reported at a greater frequency (>=2 participant difference) in the placebo group compared with the nirmatrelvir/ritonavir group were: Tachycardia (3 [0.5%] vs 1 [0.2%] participants, respectively), Activated partial thromboplastin time prolonged (12 [1.9%] vs 7 [1.1%] participants, respectively), and Blood thyroid stimulating hormone increased (7 [1.1%] vs 3 [0.5%] participants, respectively).
In the nirmatrelvir/ritonavir group, 16 (2.4%) participants discontinued study intervention due to at least 1 AE and continued the study compared with 5 (0.8%) participants in the placebo group. Of the 21 participants who discontinued study intervention in both groups, 13 participants had at least 1 TEAE that was considered by the investigator to be related to study intervention.
No participants in the nirmatrelvir/ritonavir group experienced an AE resulting in death (Grade 5), compared to 1 participant in the placebo group who experienced an SAE of COVID-19 pneumonia that resulted in death.
No clinically meaningful differences were observed between the nirmatrelvir/ritonavir and placebo groups with respect to hematology and clinical chemistry laboratory test results.
One participant in the nirmatrelvir/ritonavir group met laboratory criteria as a potential Hy's Law case at baseline; however, this was not a case of drug-induced liver injury because the liver laboratory abnormalities occurred prior to exposure of study intervention. The participant completed study intervention and no longer met the protocol definition of potential Hy's law by Day 7; liver laboratory values improved over time with ALT and AST returning to normal levels by Day 37.
No clinically meaningful findings in vital sign measurements were observed in this study. The incidence of participants with diastolic blood pressure >90 mmHg or systolic blood pressure >140 mmHg was comparable between the nirmatrelvir/ritonavir (9.1% and 9.6%, respectively) and placebo (11.6% and 11.0%, respectively) groups.
Primary Efficacy Endpoint Results:
The primary analysis result the primary objective of the study was not met. Treatment with nirmatrelvir/ritonavir reduced the median time to sustained alleviation of all targeted signs and symptoms through Day 28 by 1 day in the mITT1 analysis set who received treatment within 5 days of symptom onset, but the difference was not statistically significant (12 days vs 13 days; p=0.6027) as assessed by the log rank test (ie, no covariate adjustment).
Secondary Efficacy Endpoint Results:
All the following analyses used nominal p-values for reporting.
The observed event rate of COVID-19-related hospitalization or death from any cause through Day 28 in the mITT1 analysis set was 10 of 634 (1.577%) participants in the placebo group, and 5 of 654 (0.765%) in the nirmatrelvir/ritonavir group. After accounting for premature study discontinuation (ie, to include participants discontinued from the study before Day 28 without having experienced an event) by using the follow-up time in the Kaplan-Meier calculation, treatment with nirmatrelvir/ritonavir showed a -0.813% (95% confidence interval [CI]: -1.999 to 0.374; p=0.1796) absolute reduction (51.215% relative risk reduction), reducing the event rate from 1.587% to 0.774%. Through Day 28, there was 1 death in the placebo group and 0 deaths in the nirmatrelvir/ritonavir group.
* In the post hoc subgroup analysis by risk status at baseline, the risk reduction was more apparent in the subgroup of participants who were considered as high risk (ie, vaccinated with at least 1 risk factor) than in participants who were considered as standard risk (ie, participants who did not have risk factors and were either vaccinated or not vaccinated) (57.571% vs 36.913%).
In the mITT1 analysis set, there was 1 death in the placebo group (Day 6) and none in the nirmatrelvir/ritonavir group through Week 24.
Compared with the nirmatrelvir/ritonavir group (15 participants), more participants in the placebo group (25 participants) had COVID-19-related medical visits and reported more visits (nirmatrelvir/ritonavir: 24 visits; placebo: 36 visits). After adjusting for geographic region, symptom onset duration, baseline severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) serology status, vaccination status, and baseline viral load, the COVID-19-related medical visits occurred less frequently in the nirmatrelvir/ritonavir group at 50.2% of the rate in the placebo group, but the difference was not significant (p=0.0971).
Including participants with and without hospitalizations, the nirmatrelvir/ritonavir group reported fewer days in the hospital than in the placebo group: mean (SD) 0.049 (0.591) days for nirmatrelvir/ritonavir and 0.181 (1.787) days for placebo. Similar results were observed for non-intensive care unit (ICU) visit. No participants in the nirmatrelvir/ritonavir group reported any ICU visits. For the 3 participants in the placebo group with an ICU visit, the duration of hospitalization ranged from 10 days to 21 days.
Over the study period from Day 1 through Day 28, the proportion of participants with severe signs and symptoms was lower in the nirmatrelvir/ritonavir group (19.136%) compared with the placebo group (21.643%) (p=0.1622). Similar findings were observed at baseline (Day 1) and during treatment (Days 2 to 6), but the difference was not significant (p=0.2494 and p=0.0783, respectively). However, after treatment and during the follow-up period (Day 7 to Day 28), the proportion of participants with severe signs and symptoms was lower in the nirmatrelvir/ritonavir group compared with placebo (p=0.0280).
Treatment with nirmatrelvir/ritonavir reduced the median time to sustained resolution of all targeted COVID-19-related signs and symptoms through Day 28 by 1 day compared with placebo (15 days vs 16 days, respectively), but the mean difference was not significant (15.598 days vs 16.285 days, respectively; p=0.4298).
Reductions in the median time to sustained alleviation and sustained resolution of each targeted COVID-19 sign and symptom were observed with nirmatrelvir/ritonavir treatment compared with placebo by 2 days for stuffy or runny nose and 1 day for shortness of breath or difficulty breathing; cough; feeling hot or feverish; and sore throat (sustained alleviation) and by 2 days for headache and sore throat and by 1 day for muscle or body aches; shortness of breath or difficulty breathing; chills or shivering; cough; feeling hot or feverish; and stuffy or runny nose (sustained resolution).
Participants in the nirmatrelvir/ritonavir group were less likely to progress to a worsening status (ie, increased severity for any targeted symptom) through Day 28 compared with the placebo group, but the treatment difference was not significant (odds ratio vs placebo 0.802, p=0.1086).
Among participants with resting peripheral oxygen saturation >=95% at baseline (Day 1), twice as many participants in the placebo group than in the nirmatrelvir group had an oxygen saturation <95% (12 vs 6 participants, respectively). Participants who had a resting peripheral oxygen saturation >=95% at baseline (Day 1) were more likely to maintain those levels at Day 5 than those with a resting peripheral oxygen saturation <95% at baseline, but the treatment difference was not significant (p=0.3262).
On-treatment reduction in viral load (ie, change from baseline in viral load ribonucleic acid [RNA] concentration) was significantly (p<0.0001) larger in the nirmatrelvir/ritonavir treatment group than in the placebo group.
* Mean baseline (Day 1) (SD) log10 viral load was 6.045 (1.862) log10 copies/mL in the placebo group and 6.214 (1.794) log10 copies/mL in the nirmatrelvir/ritonavir group. After accounting for treatment, geographic region, baseline SARS-CoV-2 serology status, symptom onset duration, vaccination status, and baseline viral load, the change from baseline to Day 5 adjusted mean (standard error [SE]) reduction in log10 viral load was -2.551 (0.088) log10 copies/mL in the placebo group and -3.419 (0.084) log10 copies/mL in the nirmatrelvir/ritonavir group, reflecting an additional average reduction (95% CI) of -0.868 (-1.073 to -0.663), p<0.0001) log10 copies/mL.
* Among participants with detectable viral load at baseline (545 for nirmatrelvir/ritonavir; 517 for placebo), overall reductions in viral load over time (ie, change from baseline in viral RNA concentration through Day 14) occurred more rapidly in the nirmatrelvir/ritonavir group than in the placebo group with the difference between both groups most apparent at Day 5: Least squares mean difference (SE) log10 copies/mL: -0.736 (0.120) at Day 3; -0.834 (0.106) at Day 5; -0.231 (0.100) at Day 10; and -0.215 (0.077) at Day 14.
Pharmacokinetic Results:
Geometric mean (coefficient of variation %) nirmatrelvir concentrations, representative of maximum observed concentration (Cmax) on Day 1 (30 to 90 minutes postdose) and predose concentration (Ctrough) on Day 5 (preferably up to 2 hours predose) were 1521 (74%) ng/mL and 2566 (71%) ng/mL, respectively.
Nirmatrelvir/ritonavir reduced the time to sustained alleviation of all targeted signs and symptoms through Day 28, but the difference was not statistically significant and the study primary objective was not met; the secondary analysis results were not statistically significant despite some positive results.
The antiviral effect of nirmatrelvir/ritonavir was demonstrated by a significant reduction of SARS-CoV-2 viral load compared with placebo at Day 5.
Nirmatrelvir/ritonavir was safe and well tolerated.
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.
AN INTERVENTIONAL EFFICACY AND SAFETY, PHASE 2/3, DOUBLE-BLIND, 2 ARM STUDY TO INVESTIGATE ORALLY ADMINISTERED PF-07321332/RITONAVIR COMPARED WITH PLACEBO IN NONHOSPITALIZED SYMPTOMATIC ADULT PARTICIPANTS WITH COVID-19 WHO ARE AT LOW RISK OF PROGRESSING TO SEVERE ILLNESS
* Confirmed SARS-CoV-2 infection 5 days prior to randomization
* Initial onset of COVID-19 signs/symptoms within 5 days of randomization
* Fertile participants must agree to use a highly effective method of contraception
*Has at least one underlying medical condition associated with an increased risk of developing severe illness from COVID-19.
*History of or need for hospitalization for the medical treatment of COVID-19.
*Prior diagnosis of SARS-CoV-2 infection (reinfection)
*Known medical history of liver disease
*Receiving dialysis or have known renal impairment
*Known Human Immunodeficiency Virus (HIV) infection with viral load > 400 copies/ml or taking prohibited medications for HIV treatment
*Suspected or confirmed concurrent active systemic infection other than COVID-19
*Current or expected use of any medications or substances that are highly dependent on Cytochrome P450 3A4 (CYP3A4) for clearance or are strong inducers of CYP3A4
*Has received or is expected to receive monoclonal antibody treatment or convalescent COVID-19 plasma
*Has received any SARS-CoV-2 vaccine within 12 months of screening.
*Participating in another interventional clinical study with an investigational compound or device, including those for COVID-19
*Known prior participation in this trial or other trial involving PF-07321332
*Oxygen saturation of < 92% on room air
*Females who are pregnant or breastfeeding
Time to Sustained Alleviation of All Targeted COVID-19 Signs/Symptoms [ Time Frame: Baseline through Day 28 ]
Analysis set includes COVID-19 symptom onset 1-3 days before treatment.
* Percentage of Participants Who Experience Adverse Events (AEs) [ Time Frame: Baseline through Day 34 ]
* Percentage of Participants Who Experience an AE(s) or Serious Adverse Events (SAEs) that Leads to Study Discontinuation [ Time Frame: Baseline through Day 34 ]
* Proportion of Participants With Severe Signs/Symptoms Attributed to COVID-19 [ Time Frame: Baseline through Day 28 ]
* Time to Sustained Resolution of All Targeted COVID-19 Signs/Symptoms [ Time Frame: Baseline through Day 28 ]
* Duration of Each Targeted COVID-19 Sign/Symptom [ Time Frame: Baseline through Day 28 ]
* Proportion of Participants Progressing to a Worsening Status In 1 or More COVID-19 Signs/Symptoms [ Time Frame: Baseline through Day 28 ]
* Proportion of Participants With a Resting Peripheral Oxygen Saturation >=95% [ Time Frame: Days 1, 5 ]
* Number of COVID-19 Related Medical Visits [ Time Frame: Baseline through Day 28 ]
* Number of Days in Hospital and Intensive Care Unit (ICU) Stay in Participants With COVID-19 Related Hospitalization [ Time Frame: Baseline through Day 28 ]
* Proportion of Participants With COVID-19 Related Hospitalization or Death From Any Cause [ Time Frame: Baseline through Day 28 ]
* Proportion of Participants With Death (all cause) [ Time Frame: Baseline through Week 24 ]
* Minimal Concentration (Ctrough) of PF-07321332 [ Time Frame: Baseline through Day 5 ]
* Viral Titers Measured Via Reverse Transcription Polymerase Chain Reaction (RT-PCR) in Nasal Swabs [ Time Frame: Baseline through Day 14 ]
* Time to Sustained Alleviation of All Targeted COVID-19 Signs/Symptoms [ Time Frame: Baseline through Day 28 ]
Analysis set includes COVID-19 symptom onset 1-5 days before treatment.