Real-world effectiveness of molnupiravir and nirmatrelvir/ritonavir against mortality, hospitalization, and in-hospital outcomes among community-dwelling, ambulatory COVID-19 patients during the BA.2.2 wave in Hong Kong: an observational study
Authors: Wong Carlos K.H. , Au Ivan C.H. , Lau Kristy T.K. , Lau Eric H. Y. , Cowling Benjamin J. , Leung Gabriel M. 
Published: May 2022

Background

Evidence evaluating real-world effectiveness of oral antivirals against Omicron variants is lacking.

Methods

An unselected, territory-wide cohort of all initially non-hospitalized patients with an officially registered diagnosis of SARS-CoV-2 infection between 26th February and 3rd May 2022 during the Omicron BA.2.2 wave in Hong Kong, was identified. We undertook a retrospective cohort design as primary analysis, and case-control design as sensitivity analysis. Outpatient oral antiviral users were matched with controls using 1:10 propensity-score matching. Study outcomes were mortality, COVID-19-related hospitalization, composite outcome of in-hospital disease progression (in-hospital mortality, invasive mechanical ventilation, or intensive care unit admission) and its individual outcomes. Hazard ratios (HR) were estimated by Cox regression, and odds ratios in oral antiviral users compared with non-users by logistic regression. Subgroup analyses evaluated the associations by vaccination status and age.

Findings

Among 1,072,004 non-hospitalized COVID-19 patients, 5,257 and 5,663 were initiated molnupiravir and nirmatrelvir/ritonavir in the community setting with a median follow-up of 42 and 38 days, respectively. Molnupiravir use was associated with lower risks of mortality (HR=0·61, 95%CI=0·46-0·82, p<0·001) and in-hospital composite outcome (HR=0·64, 95%CI=0·50-0·83, p<0·001) than non-use, while that of hospitalization was comparable to controls (HR=1·06, 95%CI=0·97-1·16, p=0·191). Nirmatrelvir/ritonavir use was associated with lower risks of mortality (HR=0·25, 95%CI=0·13-0·47, p<0·001), hospitalization (HR=0·69, 95%CI=0·60-0·79, p<0·001), and in-hospital outcome (HR=0·47, 95%CI=0·31-0·71, p<0·001) than non-use. Similar protective effects of nirmatrelvir/ritonavir were observed across vaccination status (fully vaccinated versus otherwise) and age (dichotomized at 65 years), whereas those for molnupiravir were less consistent. Findings from case-control analysis broadly confirmed those of primary analysis.

Interpretation

Amid the Omicron BA.2.2 wave, early initiation of oral antivirals among non-institutionalised COVID-19 patients was associated with reduced risks of mortality and in-hospital outcomes. Nirmatrelvir/ritonavir use was associated with greater and more consistent protection than molnupiravir.

Funding

Health and Medical Research Fund, Food and Health Bureau

Research in context

Evidence before this study

Oral antivirals have been initiating in non-hospitalized COVID-19 patients to lower their risks of hospitalization and death, and hence to reduce the burden on healthcare systems. We searched Scopus and PubMed for studies until 25 May 2022 using the search terms “SARS-CoV-2 OR COVID-19” AND “molnupiravir OR Lagevrio OR EIDD-2801” OR “nirmatrelvir OR Paxlovid OR PF-07321332”. Major studies examining the outpatient use of molnupiravir and nirmatrelvir/ritonavir are MOVe-OUT and EPIC-HR trials, respectively. Both have been conducted among unvaccinated, non-hospitalized patients with mild-to-moderate COVID-19 who are at risk of progression to severe disease, during a pandemic wave of SARS-CoV-2 Delta variant. Early initiation of molnupiravir or nirmatrelvir/ritonavir within five days of symptom onset has been associated with relative risk reduction of hospitalization or death by 30% and 88%, respectively. Considering the real-world evaluation of the two oral antivirals against the currently circulating Omicron variant, only one single-center, retrospective review of solid organ transplant recipients with COVID-19 has been conducted; yet their results are unlikely generalizable to other populations given its specific patient group and small sample size. Real-world effectiveness of oral antivirals is urgently needed to inform their clinical use in COVID-19 patients, considering their vaccination status and the variant of concern.

Added value of this study

To the best of our knowledge, this is one of the first real-world studies exploring the clinical use of oral antivirals during a pandemic wave dominated by SARS-CoV-2 Omicron variant. A territory-wide, retrospective cohort study was conducted to examine the effectiveness of molnupiravir and nirmatrelvir/ritonavir in community-dwelling COVID-19 patients. Early initiation of molnupiravir or nirmatrelvir/ritonavir within five days of symptom onset was associated with significant reduction of all-cause mortality risk by 39% and 75%, respectively, compared to not using any oral antivirals. Nirmatrelvir/ritonavir use was also associated with a reduced risk of COVID-19-related hospitalization by 31%, which was consistently observed across age and vaccination status. In terms of disease progression, both oral antivirals were effective in lowering the risk of in-hospital death, which was again more substantial with nirmatrelvir/ritonavir than molnupiravir. Intriguingly, the need for invasive ventilation might be reduced among molnupiravir users compared to matched controls.

Implications of all the available evidence

Based on relative efficacy, our findings give support to current guidelines prioritizing nirmatrelvir/ritonavir use over molnupiravir in community-dwelling COVID-19 patients who are at high risk of hospitalization or progression to severe disease, should the former be accessible and clinically appropriate. Amid a pandemic wave of the Omicron variant, real-world effectiveness of oral antivirals in reducing the mortality risk of community-dwelling COVID-19 patients has been demonstrated in this study consisting mostly of the elderly and those who had not been fully vaccinated, extending beyond the evidence demonstrated in clinical trials among those of the Delta variant and who were at risk of severe COVID-19 from being overweight/obese. Several clinical trials (namely RECOVERY and PANORAMIC) and observational studies of the two oral antivirals are ongoing, and further research is needed to confirm our results in other patient populations and healthcare settings.