ABSTRACT
ImportanceMonoclonal antibody (mAb) treatment decreases hospitalization and death in outpatients with mild to moderate COVID-19; however, only intravenous administration has been evaluated in randomized clinical trials of treatment. Subcutaneous administration may expand outpatient treatment capacity and qualified staff available to administer treatment, but association with patient outcomes is understudied. ObjectiveTo evaluate whether or not, i.) subcutaneous casirivimab and imdevimab treatment is associated with reduced 28-day hospitalization/death than non-treatment among mAb-eligible patients, and ii.) subcutaneous casirivimab and imdevimab treatment is clinically and statistically similar to intravenous casirivimab and imdevimab treatment. Design, Setting, and ParticipantsProspective cohort study of outpatients in a learning health system in the United States with mild to moderate COVID-19 symptoms from July 14 to October 26, 2021 who were eligible for mAb treatment under emergency use authorization. A nontreated control group of eligible patients was also selected. InterventionSubcutaneous injection or intravenous administration of the combined single dose of casirivimab 600mg and imdevimab 600mg. Main Outcomes and MeasuresThe primary outcome was the 28-day adjusted risk ratio or adjusted risk difference for hospitalization or death. Secondary outcomes included 28-day adjusted risk ratios/differences of hospitalization, death, composite endpoint of ED admission and hospitalization, and rates of adverse events. ResultsAmong 1,956 matched adults with mild to moderate COVID-19, patients who received casirivimab and imdevimab subcutaneously had a 28-day rate of hospitalization/death of 3.4% (n=652) compared to 7.8% (n=1,304) in nontreated controls [risk ratio 0.44 (95% confidence interval: 0.28 to 0.68, p < .001)]. Among 2,185 patients treated with subcutaneous (n=969) or intravenous (n=1,216) casirivimab and imdevimab, the 28-day rate of hospitalization/death was 2.8% vs. 1.7%, respectively which resulted in an adjusted risk difference of 1.5% (95% confidence interval: -0.5% to 3.5%, p=.14). The 28-day adjusted risk differences (subcutaneous - intravenous) for death, ICU admission, and mechanical ventilation were 0.3% or less, although the 95% confidence intervals were wide. Conclusions and RelevanceSubcutaneously administered casirivimab-imdevimab is associated with reduced risk-adjusted hospitalization or death amongst outpatients with mild to moderate COVID-19 compared to no treatment and indicates low adjusted risk difference compared to patients treated intravenously. Key PointsO_ST_ABSQuestionC_ST_ABSAmong outpatients with mild to moderate COVID-19, is subcutaneously administered casirivimab and imdevimab associated with improved risk-adjusted 28-day clinical outcomes compared to non-treatment with monoclonal antibodies, and clinically similar association compared to intravenously administered casirivimab and imdevimab? FindingsAmong 1,956 propensity-matched adults, outpatients who received casirivimab and imdevimab subcutaneously had a 28-day rate of hospitalization or death of 3.4% (n=652) compared to 7.8% (n=1,304) in non-treated controls [risk ratio 0.44 (95% confidence interval: 0.28 to 0.68, p < .001)]. Among 2,185 outpatients who received subcutaneous (n=969) or intravenous (n=1,216) casirivimab and imdevimab, the 28-day rate of hospitalization/death was 2.8% vs. 1.7%, respectively, which resulted in an adjusted risk difference of 1.5% (95% confidence interval: -0.5% to 3.5%, p=.14). The 28-day adjusted risk differences comparing subcutaneous to intravenous route for death, ICU admission, and mechanical ventilation were 0.3% or less, although the 95% confidence intervals were wide. MeaningSubcutaneously administered casirivimab and imdevimab is associated with reduced hospitalization or death amongst outpatients with mild to moderate COVID-19 compared to no treatment, and has a small, adjusted risk difference compared to patients treated intravenously.
ABSTRACT
BackgroundNeutralizing monoclonal antibodies (mAb) targeting SARS-CoV-2 decrease hospitalization and death in patients with mild to moderate Covid-19. Yet, their clinical use is limited, and comparative effectiveness is unknown. MethodsWe present the first results of an ongoing, learning health system adaptive platform trial to expand mAb treatment to all eligible patients and evaluate the comparative effectiveness of available mAbs. The trial launched March 10, 2021. Results are reported as of June 25, 2021 due to the U.S. federal decision to pause distribution of bamlanivimab-etesevimab; patient follow-up concluded on July 23, 2021. Patients referred for mAb who met Emergency Use Authorization criteria were provided a random mAb allocation of bamlanivimab, bamlanivimab-etesevimab, or casirivimab-imdevimab with a therapeutic interchange policy. The primary outcome was hospital-free days (days alive and free of hospital) within 28 days, where patients who died were assigned -1 day. The primary analysis was a Bayesian cumulative logistic model of all patients treated at an infusion center or emergency department, adjusting for treatment location, age, sex, and time. Inferiority was defined as a 99% posterior probability of an odds ratio < 1. Equivalence was defined as a 95% posterior probability that the odds ratio is within a given bound. ResultsPrior to trial launch, 3.1% (502) of 16,345 patients who were potentially eligible by an automated electronic health record (EHR) screen received mAb. During the trial period, 23.2% (1,201) of 5,173 EHR-screen eligible patients were treated, a 7.5-fold increase. After including additional referred patients from outside the health system, a total of 1,935 study patients received mAb therapy (128 bamlanivimab, 885 bamlanivimab-etesevimab, 922 casirivimab-imdevimab). Mean age ranged from 55 to 57 years, half were female (range, 53% to 54%), and 17% were Black (range, 12% to 19%). Median hospital-free days were 28 (IQR, 28 to 28) for each mAb group. Hospitalization varied between groups (bamlanivimab, 12.5%; bamlanivimab-etesevimab, 14.7%, casirivimab-imdevimab, 14.3%). Relative to casirivimab-imdevimab, the median adjusted odds ratios were 0.58 (95% credible interval (CI), 0.30 to 1.16) and 0.94 (95% CI, 0.72 to 1.24) for the bamlanivimab and bamlanivimab-etesevimab groups, respectively. These odds ratios yielded 91% and 94% probabilities of inferiority of bamlanivimab versus bamlanivimab-etesevimab and casirivimab-imdevimab respectively, and an 86% probability of equivalence between bamlanivimab-etesevimab and casirivimab-imdevimab, at the prespecified odds ratio bound of 0.25. Twenty-one infusion-related adverse events occurred in 0% (0/128), 1.4% (12/885), and 1.0% (9/922) of patients treated with bamlanivimab, bamlanivimab-etesevimab, and casirivimab-imdevimab, respectively. ConclusionIn non-hospitalized patients with mild to moderate Covid-19, bamlanivimab, compared to bamlanivimab-etesevimab and casirivimab-imdevimab, resulted in 91% and 94% probabilities of inferiority with regards to odds of improvement in hospital-free days within 28 days. There was an 86% probability of equivalence between bamlanivimab-etesevimab and casirivimab-imdevimab at an odds ratio bound of 0.25. However, the trial was unblinded early due to federal distribution decisions, and no mAb met prespecified criteria for statistical inferiority or equivalence. (ClinicalTrials.gov, NCT04790786).
