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Effectiveness of COVID-19 Vaccines in Ambulatory and Inpatient Settings
Quick Takes
- This is a retrospective study by the VISION Network; a collaboration between the CDC and seven US health care systems totaling 187 hospitals, 167 EDs, and 54 urgent care clinics.
- The analytic sample included 41,552 hospitalizations and 21,522 ED or urgent care clinic visits, of whom 4,321 and 3,251 patients had laboratory-confirmed SARS-CoV-2 infection, respectively.
- Full vaccination with mRNA-based vaccines had approximately 90% effectiveness in reducing the odds of hospitalization for COVID-19, while the effectiveness of the Ad26.COV2.S vaccine was approximately 70%.
Study Questions:
How effective is vaccination for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) in preventing hospitalization, intensive care unit (ICU) admission, and emergency/urgent care clinic visits for symptoms consistent with coronavirus disease 2019 (COVID-19)?
Methods:
The Centers for Disease Control and Prevention (CDC), in collaboration with seven US health care systems including a total of 187 hospitals, 167 emergency departments (EDs), and 54 urgent care clinics make up the VISION Network. This study leverages the VISION Network to assess the effectiveness of COVID-19 vaccines in reducing SARS-CoV-2 infection–associated hospitalizations, ICU admissions, or visits to EDs or urgent care clinics from January 1–June 22, 2021. The study population was limited to vaccine-eligible adults (≥50 years). A patient with COVID-19 was defined as a person with at least one International Classification of Diseases (ICD) code that was consistent with COVID-19–like illness and at least one positive SARS-CoV-2 test result within 14 days before to <72 hours after an event (hospital admission, ED, or urgent care visit). COVID-19 vaccination status was documented by state immunization registries. They used a test-negative design to estimate vaccine effectiveness by comparing the odds of a positive test for SARS-CoV-2 infection among vaccinated patients with those among unvaccinated patients. Vaccine effectiveness was adjusted with weights based on propensity for vaccination scores and according to age, geographic region, calendar time, and local virus circulation.
Results:
The analytic sample included 41,552 hospitalizations and 21,522 ED or urgent care clinic visits, of whom 4,321 and 3,251 patients had laboratory-confirmed SARS-CoV-2 infection, respectively. The effectiveness of full messenger RNA (mRNA) vaccination (≥14 days after the second dose) was 89% (95% confidence interval [CI], 87-91) against laboratory-confirmed SARS-CoV-2 infection leading to hospitalization, 90% (95% CI, 86-93) against infection leading to an ICU admission, and 91% (95% CI, 89-93) against infection leading to an ED or urgent care clinic visit.
Effectiveness was similar with the BNT162b2 (Pfizer–BioNTech) and mRNA-1273 (Moderna) vaccines in those fully vaccinated, across age, chronic medical conditions, and race. Vaccine effectiveness with respect to COVID-19–associated hospitalization was null 0-13 days after the first dose. Vaccine-effectiveness point estimates for full mRNA-based vaccination remained consistently high (>80%) through at least 112 days after the second dose.
The effectiveness of the Ad26.COV2.S (Johnson & Johnson–Janssen [JNJ]) vaccine was 68% (95% CI, 50-79) against SARS-CoV-2 infection leading to hospitalization and 73% (95% CI, 59-82) against infection leading to an ED or urgent care clinic visit.
Conclusions:
COVID-19 vaccines in the United States were highly effective against SARS-CoV-2 infection requiring hospitalization, ICU admission, or an ED or urgent care clinic visit.
Perspective:
This study addresses the effectiveness of the SARS-CoV-2 vaccines in a real-world setting, examining specifically the outcomes of hospitalization, admission to an ICU, or an urgent care visit (ED or clinic). The authors perform in-depth sensitivity analyses across age, race, and comorbidities and provide reassuring data of the effectiveness of all three authorized vaccines in the United States in preventing severe COVID-19. The mRNA vaccines demonstrated higher effectiveness than the Ad26.COV2.S (JNJ) vaccine, although the number of patients who had received the JNJ vaccine was much smaller, limiting the authors’ ability to derive strong conclusions. The study does not address the patient population younger than 50 years old, different viral lineages, and mostly encompasses the timeline during which the vaccine was available for those with chronic conditions. Nevertheless, this is yet another study supporting the use of vaccines as the optimal strategy to reduce the risk of severe illness from COVID-19.
Clinical Topics: COVID-19 Hub, Prevention
Keywords: Ambulatory Care, Coronavirus, Coronavirus Infections, COVID-19, COVID-19 Vaccines, COVID-19 Testing, Delivery of Health Care, Emergency Service, Hospital, Inpatients, Intensive Care Units, Mass Vaccination, Primary Prevention, RNA, Messenger, SARS-CoV-2, Vaccination, Vaccine Potency
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