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.
The Centers for Disease Control and Prevention (CDC), in collaboration with seven U.S. healthcare systems and research centers with integrated medical, laboratory and vaccination records, established the VISION Network to assess the effectiveness of COVID-19 vaccines with respect to laboratory-confirmed SARS-CoV-2 infection–associated hospitalizations, ICU admissions or visits to emergency departments or urgent care clinics from January 1 through June 22, 2021.
The CDC 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). They 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.
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 (days from January 1, 2021, to the index date for each medical visit) and local virus circulation.
The effectiveness of full messenger RNA (mRNA) vaccination (≥14 days after the second dose) was 89% against laboratory-confirmed SARS-CoV-2 infection leading to hospitalization, 90% against infection leading to an ICU admission and 91% 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% against laboratory-confirmed SARS-CoV-2 infection leading to hospitalization and 73% against infection leading to an emergency department or urgent care clinic visit.
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.
Three currently authorized coronavirus disease 2019 (COVID-19) vaccines in the United States were shown to be highly effective in preventing symptomatic COVID-19 in randomized, placebo-controlled phase 3 trials and in subsequent observational vaccine-effectiveness studies of messenger RNA (mRNA) COVID-19 vaccines. However, less is known about how well these vaccines protect against more severe illness due to severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) resulting in hospitalization, admission to an intensive care unit (ICU), or ambulatory care in an emergency department or urgent care clinic.
In addition, estimates of vaccine effectiveness have been limited in populations that have been disproportionately affected by COVID-19, including older adults, persons with chronic medical conditions and Black or Hispanic populations. Data are lacking from real-world estimates of effectiveness of all three COVID-19 vaccines authorized in the United States: BNT162b2 (Pfizer–BioNTech), mRNA-1273 (Moderna), and Ad26.COV2.S (Johnson & Johnson–Janssen):
- First, mRNA-based vaccines were highly effective among adults who were 85 years of age or older and persons with chronic medical conditions. This finding is reassuring, given that these groups can have impaired immune responses to other vaccines and are most at risk for severe and prolonged manifestations of COVID-19 and death.
- Second, in Black adults and Hispanic adults, who have been disproportionately affected by COVID-19, mRNA-based vaccines were similarly effective with respect to COVID-19–associated hospitalization and an emergency department or urgent care clinic visit.
- Third, the effectiveness of full mRNA-based vaccination remained consistently high at least until 112 days after the second dose, which was the longest interval since vaccination during our study period.
- Fourth, the effectiveness of all three authorized COVID-19 vaccines in the United States was examined.
