Real-world effectiveness of early molnupiravir and nirmatrelvir/ritonavir among hospitalized, non-oxygen-dependent COVID-19 patients on admission during Hong Kong’s Omicron BA.2 wave: 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

Effectiveness of oral antivirals in mild-to-moderate COVID-19 patients is urgently needed. This retrospective cohort study aims to evaluate the clinical and virologic outcomes associated with molnupiravir and nirmatrelvir/ritonavir use in COVID-19 patients during a pandemic wave dominated by the Omicron BA.2 subvariant.

Methods

We analyzed data from a territory-wide retrospective cohort of hospitalized patients with confirmed diagnosis of SARS-CoV-2 infection from 26th February 2022 to 26th April 2022 in Hong Kong. Oral antiviral users were matched with controls using propensity-score matching in a ratio of 1:1. Study outcomes were all-cause mortality, a composite outcome of disease progression (all-cause mortality, initiation of invasive mechanical ventilation [IMV], intensive care unit admission, or the need for oxygen therapy) and their individual outcomes, and time to achieving lower viral burden of cycle threshold (Ct) value ≥30 cycles. Hazard ratios (HR) of event outcomes were estimated using Cox regression models.

Results

Among 40,776 hospitalized patients with SARS-CoV-2 infection over a mean follow-up of 41.3 days with 925,713 person-days, this study included 1,856 molnupiravir users, 890 nirmatrelvir/ritonavir users and 2,746 control patients not initially requiring oxygen therapy at baseline after propensity-score matching. Oral antiviral use was associated with significantly lower risks of all-cause mortality (molnupiravir: HR=0.48, 95%CI=0.40-0.59, p<0.0001; nirmatrelvir/ritonavir: HR=0.34, 95%CI=0.23-0.50, p<0.0001), the composite outcome of disease progression (molnupiravir: HR=0.60, 95%CI=0.52-0.69, p<0.0001; nirmatrelvir/ritonavir: HR=0.57, 95%CI=0.45-0.72, p<0.0001), and the need for oxygen therapy (molnupiravir: HR=0.69, 95%CI=0.57-0.83, p=0.00011; nirmatrelvir/ritonavir: HR=0.73, 95%CI=0.54-0.97, p=0.032) than non-use. Time to achieving lower viral burden was significantly shorter among oral antiviral users than matched controls (molnupiravir: HR=1.38, 95%CI=1.15-1.64, p=0.0046; nirmatrelvir/ritonavir: HR=1.38, 95%CI=1.07-1.78, p=0.013).

Conclusions

Against Omicron BA.2, initiation of novel oral antiviral treatment in hospitalized patients not requiring any oxygen therapy was associated with lower risks of all-cause mortality and disease progression, in addition to achieving low viral burden faster. Our findings support the early use of oral antivirals in COVID-19 patients who do not require supplemental oxygen on admission.

Funding

Health and Medical Research Fund, Food and Health Bureau, Government of the Hong Kong SAR

Research in context

Evidence before this study

The medical and research community are actively exploring the use of oral antivirals in COVID-19 patients to lower their risks of hospitalization and death, and to reduce the burden on healthcare systems. We searched Scopus and PubMed for studies until 13th 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 safety and efficacy of molnupiravir include MOVe-IN and MOVe-OUT trials conducted in hospitalized and non-hospitalized COVID-19 patients, respectively. Clinical evidence for the use of ritonavir-boosted nirmatrelvir came from the EPIC-HR trial conducted among non-hospitalized adults with COVID-19. While no clinical benefits have been observed with molnupiravir use in the inpatient setting among patients with moderate-to-severe COVID-19, early initiation of molnupiravir or nirmatrelvir/ritonavir within 5 days of symptom onset in non-hospitalized patients with mild-to-moderate COVID-19 and risk factors for progression to severe disease has been associated with relative risk reduction of hospitalization or death by 30% and 88%, respectively. Notably, these clinical trials were conducted prior to the prevalence of Omicron variant, and the efficacy of oral antivirals against this current variant of concern can only be inferred from experimental evidence to date. Real-world evidence of oral antiviral use in patients with SARS-CoV-2 infection of Omicron variant is lacking.

Added value of this study

To the best of our knowledge, this is the first real-world study exploring the inpatient use of oral antivirals during a pandemic wave dominated by SARS-CoV-2 Omicron variant. We conducted a territory-wide, retrospective cohort study to examine the effectiveness of molnupiravir and nirmatrelvir/ritonavir in COVID-19 patients who did not require supplemental oxygen on admission in Hong Kong. Early initiation of oral antivirals within 2 days of admission was associated with significantly lower risks of all-cause mortality and disease progression, in addition to achieving low viral burden faster than their respective matched controls. Oral antiviral use was also associated with a reduced need for oxygen therapy than non-use.

Implications of all the available evidence

Current guidelines are now prioritizing the distribution of oral antivirals to those who do not require supplemental oxygen, but who are at the highest risk of disease progression. Our study cohort reflected such prescription pattern in real-world clinical practice, consisting of mostly the elderly with multiple pre-existing comorbidities and who had not been fully vaccinated. The antiviral effect and mortality benefit observed in this patient cohort support the use of oral antivirals in COVID-19 patients who do not require supplemental oxygen on admission during a pandemic wave of Omicron variant. Ongoing research will inform the safety and effectiveness of oral antivirals in specific patient populations (by vaccination status and viral variants), drug combinations, and different healthcare settings.