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Effectiveness of mRNA COVID-19 Vaccination in Preventing Symptomatic Infection in Health-Care Personnel


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As reported in The New England Journal of Medicine by Pilishvili et al for the Vaccine Effectiveness among Healthcare Personnel Study Team, a case-control study has shown that full vaccination with the COVID-19 mRNA vaccines was highly effective in preventing symptomatic COVID-19 infection in U.S. health-care personnel, including among those with elevated risk for severe infection and across all racial/ethnic groups.

Study Details

The test-negative case-control study involved 1,482 case participants and 3,449 control participants from 25 states tested between December 2020 and May 2021. Cases had a positive polymerase chain reaction (PCR) or antigen-based test for SARS–CoV-2 and at least one COVID-19–like symptom. Controls had a negative PCR test for SARS–CoV-2, irrespective of symptoms, and were matched to cases according to the week and site of the test.

Vaccine effectiveness was evaluated for partial vaccination (assessed from 14 days after receipt of the first dose through 6 days after receipt of the second dose) and complete vaccination (assessed at ≥ 7 days after receipt of the second dose). The estimates of vaccine effectiveness are from analysis adjusting for age, race/ethnic group, presence of underlying conditions, and close contact with patients infected with COVID-19 in the workplace or persons infected with COVID-19 outside the workplace.  

The BNT162b2 and mRNA-1273 vaccines were highly effective under real-world conditions in preventing symptomatic COVID-19 in health-care personnel, including those at risk for severe COVID-19 and those in racial and ethnic groups that have been disproportionately affected by the pandemic.
— Pilishvili et al

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Key Findings

For the Pfizer-BioNTech BNT162b2 vaccine and Moderna mRNA-1273 vaccines, effectiveness estimates were 77.6% (95% confidence interval [CI] = 70.9%–82.7%) and 88.9% (95% CI = 78.7%–94.2%) for partial vaccination and 88.8% (95% CI = 84.6%–91.8%) and 96.3% (95% CI = 91.3%–98.4%) for full vaccination, respectively.

Effectiveness estimates with full vaccination with either vaccine were:

  • 90.3% and 90.7% for participants aged < 50 and ≥ 50 years
  • 90.1% for White, 94.8% for Black, 89.4% for Hispanic/Latinx, 89.3% for Asian/Pacific Islander, and 93.7% for American Indian or Alaska Native participants
  • 90.3%, 88.5%, 89.4%, and 91.1% for participants with one or more, two or more, three or more, and no underlying conditions or risk factors for severe disease.

In a combined group of partially and completely vaccinated participants with immunocompromising conditions, vaccine effectiveness was 39.1%.

Analysis of estimated vaccine effectiveness in 2-week intervals after receipt showed highest effectiveness during weeks 3 and 4 after the second dose (96.3%, 95% CI = 92.5%–98.2%). Estimated effectiveness rates were lower during weeks 9 through 14, but the 95% confidence intervals were wide and overlapping.

The investigators concluded, “The BNT162b2 and mRNA-1273 vaccines were highly effective under real-world conditions in preventing symptomatic COVID-19 in health-care personnel, including those at risk for severe COVID-19 and those in racial and ethnic groups that have been disproportionately affected by the pandemic.”

Disclosure: The study was funded by the Centers for Disease Control and Prevention. For full disclosures of the study authors, visit nejm.org.

The content in this post has not been reviewed by the American Society of Clinical Oncology, Inc. (ASCO®) and does not necessarily reflect the ideas and opinions of ASCO®.
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