Vaccine Effectiveness of Primary Series and Booster Doses against Omicron Variant COVID-19-Associated Hospitalization in the United States

Objectives: To compare the effectiveness of a primary COVID-19 vaccine series plus a booster dose with a primary series alone for the prevention of Omicron variant COVID-19 hospitalization. Design: Multicenter observational case-control study using the test-negative design to evaluate vaccine effectiveness (VE). Setting: Twenty-one hospitals in the United States (US). Participants: 3,181 adults hospitalized with an acute respiratory illness between December 26, 2021 and April 30, 2022, a period of SARS-CoV-2 Omicron variant (BA.1, BA.2) predominance. Participants included 1,572 (49%) case-patients with laboratory confirmed COVID-19 and 1,609 (51%) control patients who tested negative for SARS-CoV-2. Median age was 64 years, 48% were female, and 21% were immunocompromised; 798 (25%) were vaccinated with a primary series plus booster, 1,326 (42%) were vaccinated with a primary series alone, and 1,057 (33%) were unvaccinated. Main Outcome Measures: VE against COVID-19 hospitalization was calculated for a primary series plus a booster and a primary series alone by comparing the odds of being vaccinated with each of these regimens versus being unvaccinated among cases versus controls. VE analyses were stratified by immune status (immunocompetent; immunocompromised) because the recommended vaccine schedules are different for these groups. The primary analysis evaluated all COVID-19 vaccine types combined and secondary analyses evaluated specific vaccine products. Results: Among immunocompetent patients, VE against Omicron COVID-19 hospitalization for a primary series plus one booster of any vaccine product dose was 77% (95% CI: 71-82%), and for a primary series alone was 44% (95% CI: 31-54%) (p<0.001). VE was higher for a boosted regimen than a primary series alone for both mRNA vaccines used in the US (BNT162b2: primary series plus booster VE 80% (95% CI: 73-85%), primary series alone VE 46% (95% CI: 30-58%) [p<0.001]; mRNA-1273: primary series plus booster VE 77% (95% CI: 67-83%), primary series alone VE 47% (95% CI: 30-60%) [p<0.001]). Among immunocompromised patients, VE for a primary series of any vaccine product against Omicron COVID-19 hospitalization was 60% (95% CI: 41-73%). Insufficient sample size has accumulated to calculate effectiveness of boosted regimens for immunocompromised patients. Conclusions: Among immunocompetent people, a booster dose of COVID-19 vaccine provided additional benefit beyond a primary vaccine series alone for preventing COVID-19 hospitalization due to the Omicron variant.

Clinical Severity and mRNA Vaccine Effectiveness for Omicron, Delta, and Alpha SARS-CoV-2 Variants in the United States: A Prospective Observational Study

ObjectivesTo characterize the clinical severity of COVID-19 caused by Omicron, Delta, and Alpha SARS-CoV-2 variants among hospitalized adults and to compare the effectiveness of mRNA COVID-19 vaccines to prevent hospitalizations caused by each variant. DesignA case-control study of 11,690 hospitalized adults. SettingTwenty-one hospitals across the United States. ParticipantsThis study included 5728 cases hospitalized with COVID-19 and 5962 controls hospitalized without COVID-19. Cases were classified into SARS-CoV-2 variant groups based on viral whole genome sequencing, and if sequencing did not reveal a lineage, by the predominant circulating variant at the time of hospital admission: Alpha (March 11 to July 3, 2021), Delta (July 4 to December 25, 2021), and Omicron (December 26, 2021 to January 14, 2022). Main Outcome MeasuresVaccine effectiveness was calculated using a test-negative design for COVID-19 mRNA vaccines to prevent COVID-19 hospitalizations by each variant (Alpha, Delta, Omicron). Among hospitalized patients with COVID-19, disease severity on the WHO Clinical Progression Ordinal Scale was compared among variants using proportional odds regression. ResultsVaccine effectiveness of the mRNA vaccines to prevent COVID-19-associated hospitalizations included: 85% (95% CI: 82 to 88%) for 2 vaccine doses against Alpha; 85% (95% CI: 83 to 87%) for 2 doses against Delta; 94% (95% CI: 92 to 95%) for 3 doses against Delta; 65% (95% CI: 51 to 75%) for 2 doses against Omicron; and 86% (95% CI: 77 to 91%) for 3 doses against Omicron. Among hospitalized unvaccinated COVID-19 patients, severity on the WHO Clinical Progression Scale was higher for Delta than Alpha (adjusted proportional odds ratio [aPOR] 1.28, 95% CI: 1.11 to 1.46), and lower for Omicron than Delta (aPOR 0.61, 95% CI: 0.49 to 0.77). Compared to unvaccinated cases, severity was lower for vaccinated cases for each variant, including Alpha (aPOR 0.33, 95% CI: 0.23 to 0.49), Delta (aPOR 0.44, 95% CI: 0.37 to 0.51), and Omicron (aPOR 0.61, 95% CI: 0.44 to 0.85). ConclusionsmRNA vaccines were highly effective in preventing COVID-19-associated hospitalizations from Alpha, Delta, and Omicron variants, but three vaccine doses were required to achieve protection against Omicron similar to the protection that two doses provided against Delta and Alpha. Among adults hospitalized with COVID-19, Omicron caused less severe disease than Delta, but still resulted in substantial morbidity and mortality. Vaccinated patients hospitalized with COVID-19 had significantly lower disease severity than unvaccinated patients for all the variants.

Effectiveness of SARS-CoV-2 mRNA Vaccines for Preventing Covid-19 Hospitalizations in the United States

BackgroundAs SARS-CoV-2 vaccination coverage increases in the United States (US), there is a need to understand the real-world effectiveness against severe Covid-19 and among people at increased risk for poor outcomes. MethodsIn a multicenter case-control analysis of US adults hospitalized March 11 - May 5, 2021, we evaluated vaccine effectiveness to prevent Covid-19 hospitalizations by comparing odds of prior vaccination with an mRNA vaccine (Pfizer-BioNTech or Moderna) between cases hospitalized with Covid-19 and hospital-based controls who tested negative for SARS-CoV-2. ResultsAmong 1210 participants, median age was 58 years, 22.8% were Black, 13.8% were Hispanic, and 20.6% had immunosuppression. SARS-CoV-2 lineage B.1.1.7 was most common variant (59.7% of sequenced viruses). Full vaccination (receipt of two vaccine doses [≥]14 days before illness onset) had been received by 45/590 (7.6%) cases and 215/620 (34.7%) controls. Overall vaccine effectiveness was 86.9% (95% CI: 80.4 to 91.2%). Vaccine effectiveness was similar for Pfizer-BioNTech and Moderna vaccines, and highest in adults aged 18-49 years (97.3%; 95% CI: 78.9 to 99.7%). Among 45 patients with vaccine-breakthrough Covid hospitalizations, 44 (97.8%) were [≥]50 years old and 20 (44.4%) had immunosuppression. Vaccine effectiveness was lower among patients with immunosuppression (59.2%; 95% CI: 11.9 to 81.1%) than without immunosuppression (91.3%; 95% CI: 85.5 to 94.7%). ConclusionDuring March-May 2021, SARS-CoV-2 mRNA vaccines were highly effective for preventing Covid-19 hospitalizations among US adults. SARS-CoV-2 vaccination was beneficial for patients with immunosuppression, but effectiveness was lower in the immunosuppressed population.

Real-World Effectiveness and Tolerability of Monoclonal Antibodies for Ambulatory Patients with Early COVID-19

ImportanceInterventions to reduce hospitalization of patients with COVID-19 are urgently needed. Randomized trials for efficacy suggest that anti-SARS-CoV2 neutralizing monoclonal antibodies (MAb) may reduce medically-attended visits and hospitalization but effectiveness has not been confirmed in a real-world setting. ObjectiveEstimate the effectiveness of MAb infusion in a real-world cohort of ambulatory patients with early symptomatic COVID-19 at high risk for hospitalization. DesignQuasi-experimental observational cohort study using target trial emulation and causal inference methodology in pre-and post-implementation groups. SettingInfusion centers and urgent care clinics within an integrated healthcare system in the United States Participants13,534 high-risk adult outpatients with symptomatic, laboratory-confirmed COVID-19 within 7 days of symptom onset. ExposuresA single intravenous infusion of either bamlanivimab 700 mg or casirivimab/imdevimab 1200 mg/1200 mg. Main Outcomes and MeasuresThe primary outcome was emergency department visit or hospitalization within 14 days of positive test. Patients who received MAb infusion were compared to contemporaneous controls using inverse probability of treatment weighting, and to a pre-implementation cohort using propensity-weighted interrupted time series analysis. An exploratory analysis compared effectiveness of casirivimab/imdevimab and bamlanivimab. Results7404 patients who would have been MAb-eligible were identified in a pre-implementation cohort (July 1-November 27, 2020). In the post-implementation period (November 28, 2020-January 28, 2021), 594 received MAb treatment and 5536 MAb-eligible patients did not. Among Mab recipients, 479 (80.6%) received bamlanivimab and 115 (19.4%) casirivimab/imdevimab. The primary outcome occurred in 75 (12.6%) MAb recipients, 1018 (18.4%) contemporaneous controls, and 1525 (20.6%) patients in the pre-implementation cohort. MAb treatment was associated with fewer subsequent emergency department visits and hospitalizations (odds ratio estimating the average treatment effect 0.69, 95% CI 0.60-0.79). After implementation, propensity-weighted probability of emergency department visit or hospitalization decreased by 0.7% per day (95% CI 0.03-0.10%, p<0.001). Overall, 7 (1.2%) MAb patients experienced an adverse event; two (0.3%) were considered serious. In the exploratory analysis, the effect of casirivimab/imdevimab versus bamlanivimab was not significant (OR 0.52, 95% CI 0.17-1.63, p=0.26). Conclusions and RelevanceMAb treatment of high-risk ambulatory patients with early COVID-19 was well-tolerated and effective at preventing the need for subsequent medically-attended care. Key Points SectionO_ST_ABSQuestionC_ST_ABSWhat is the real-world effectiveness of COVID-19 monoclonal neutralizing antibody (MAb) infusions in high-risk, ambulatory patients? Findings594 high-risk, early-symptomatic adults with COVID-19 treated with MAb infusion were compared to 5536 contemporaneous controls using inverse probability of treatment weighting, and to 7404 patients in a pre-implementation cohort using propensity-weighted interrupted time series analysis. MAb treatment was associated with fewer subsequent emergency department visits and hospitalizations (odds ratio 0.69 (95% CI 0.60-0.79). After MAb implementation the probability of emergency department visit or hospitalization decreased by 0.7% per day, 95% CI 0.03-0.10%, p<0.001). MeaningMonoclonal antibody infusion within seven days of symptom onset in high-risk ambulatory adults with COVID-19 appears to prevent subsequent emergency department visits and hospitalization. Further evaluation of the differences between specific Mab products is warranted.

Simple Scoring Tool to Estimate Risk of Hospitalization and Mortality in Ambulatory and Emergency Department Patients with COVID-19

BackgroundAccurate methods of identifying patients with COVID-19 who are at high risk of poor outcomes has become especially important with the advent of limited-availability therapies such as monoclonal antibodies. Here we describe development and validation of a simple but accurate scoring tool to classify risk of hospitalization and mortality. MethodsAll consecutive patients testing positive for SARS-CoV-2 from March 25-October 1, 2020 within the Intermountain Healthcare system were included. The cohort was randomly divided into 70% derivation and 30% validation cohorts. A multivariable logistic regression model was fitted for 14-day hospitalization. The optimal model was then adapted to a simple, probabilistic score and applied to the validation cohort and evaluated for prediction of hospitalization and 28-day mortality. Results22,816 patients were included; mean age was 40 years, 50.1% were female and 44% identified as non-white race or Hispanic/Latinx ethnicity. 6.2% required hospitalization and 0.4% died. Criteria in the simple model included: age (0.5 points per decade); high-risk comorbidities (2 points each): diabetes mellitus, severe immunocompromised status and obesity (body mass index[≥]30); non-white race/Hispanic or Latinx ethnicity (2 points), and 1 point each for: male sex, dyspnea, hypertension, coronary artery disease, cardiac arrythmia, congestive heart failure, chronic kidney disease, chronic pulmonary disease, chronic liver disease, cerebrovascular disease, and chronic neurologic disease. In the derivation cohort (n=16,030) area under the receiver-operator characteristic curve (AUROC) was 0.82 (95% CI 0.81-0.84) for hospitalization and 0.91 (0.83-0.94) for 28-day mortality; in the validation cohort (n=6,786) AUROC for hospitalization was 0.8 (CI 0.78-0.82) and for mortality 0.8 (CI 0.69-0.9). ConclusionA prediction score based on widely available patient attributes accurately risk stratifies patients with COVID-19 at the time of testing. Applications include patient selection for therapies targeted at preventing disease progression in non-hospitalized patients, including monoclonal antibodies. External validation in independent healthcare environments is needed.