Effectiveness of Covid-19 Vaccines in Ambulatory and Inpatient Care Settings

Abstract

Background: There are limited data on the effectiveness of the vaccines against symptomatic coronavirus disease 2019 (Covid-19) currently authorized in the United States with respect to hospitalization, admission to an intensive care unit (ICU), or ambulatory care in an emergency department or urgent care clinic.

Methods: We conducted a study involving adults (≥50 years of age) with Covid-19-like illness who underwent molecular testing for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). We assessed 41,552 admissions to 187 hospitals and 21,522 visits to 221 emergency departments or urgent care clinics during the period from January 1 through June 22, 2021, in multiple states. The patients' vaccination status was documented in electronic health records and immunization registries. We 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 (days from January 1, 2021, to the index date for each medical visit), and local virus circulation.

Results: The effectiveness of full messenger RNA (mRNA) vaccination (≥14 days after the second dose) was 89% (95% confidence interval [CI], 87 to 91) against laboratory-confirmed SARS-CoV-2 infection leading to hospitalization, 90% (95% CI, 86 to 93) against infection leading to an ICU admission, and 91% (95% CI, 89 to 93) against infection leading to an emergency department or urgent care clinic visit. The effectiveness of full vaccination with respect to a Covid-19-associated hospitalization or emergency department or urgent care clinic visit was similar with the BNT162b2 and mRNA-1273 vaccines and ranged from 81% to 95% among adults 85 years of age or older, persons with chronic medical conditions, and Black or Hispanic adults. The effectiveness of the Ad26.COV2.S vaccine was 68% (95% CI, 50 to 79) against laboratory-confirmed SARS-CoV-2 infection leading to hospitalization and 73% (95% CI, 59 to 82) against infection leading to an emergency department 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 emergency department or urgent care clinic visit. This vaccine effectiveness extended to populations that are disproportionately affected by SARS-CoV-2 infection. (Funded by the Centers for Disease Control and Prevention.).

Figure 1. Estimated Vaccine Effectiveness against SARS-CoV-2 Infection Leading to Hospitalization or an Emergency Department or Urgent Care Clinic Visit, According to the Type of Vaccine.

Patients who were partially vaccinated with one dose of a messenger RNA (mRNA)–based vaccine received the first dose at least 14 days before the index date for the medical visit and had not received the second dose by the index date. Patients who were partially vaccinated with two doses of an mRNA-based vaccine received the second dose 1 to 13 days before the index date. Fully vaccinated patients received a single dose of the Ad26.COV2.S vaccine or the second dose of an mRNA-based vaccine at least 14 days before the index date. CI denotes confidence interval, and SARS-CoV-2 severe acute respiratory syndrome coronavirus 2.

Figure 2. Estimated Effectiveness of Full Two-Dose mRNA Vaccination against SARS-CoV-2 Infection Leading to Hospitalization, According to Age, Race or Ethnic Group, and Underlying Medical Conditions.

Figure 3. Estimated Effectiveness of mRNA-Based Vaccination against SARS-CoV-2 Infection Leading to Hospitalization or an Emergency Department or Urgent Care Visit, According to the Days since the Most Recent Dose Was Administered.

The total number of hospitalizations shown is higher than the total number in the main analysis because this secondary analysis was conducted weeks after the main analysis and incorporated updated information from vaccination records and registries; specifically, an additional 212 hospitalizations among unvaccinated patients and 831 hospitalizations among vaccinated patients with confirmed vaccination status were included.

Figure 4. Estimated Effectiveness of Full Two-Dose mRNA-Based Vaccination against SARS-CoV-2 Infection Leading to an Emergency Department or Urgent Care Clinic Visit, According to Age, Race or Ethnic Group, and Underlying Medical Conditions.