Older adults were highly protected, CDC analysis found

The real-world efficacy of Covid-19 vaccines for preventing hospitalization and death has been shown in study after study, and now new research from the U.S. Centers for Disease Control and Prevention confirms the vaccine’s effectiveness against another key Covid outcome—infection requiring a hospital emergency department or urgent care clinic visit.

The multi-state analysis of more than 63,000 medical visits for suspected Covid-19 in the first 6 months of this year confirmed the vaccine’s effectiveness in a population at high risk for developing severe disease—adults in their 50s and older.

Full vaccination with either the Pfizer-BioNTech or Moderna mRNA vaccine was found by CDC investigators to be 91% effective against lab-confirmed Covid-19 leading to an emergency department or urgent care visit and 89% effective against infection leading to hospitalization. Vaccination with the single-dose Johnson & Johnson Ad26.COV2.S vaccine was found to be 73% effective against confirmed Covid-19 leading to an emergency department or urgent care visit and 68% effective against hospitalization due to SARS-CoV-2 infection.

Findings from the CDC investigation were published online Sept. 8 in New England Journal of Medicine.

Along with seven major U.S. health care systems and research centers, the CDC recently 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, and visits to emergency departments or urgent care clinics during the first 6 months of the nationwide Covid-19 vaccine roll out.

All seven network partners contributed data on hospitalizations and ICU visits from a total of 187 hospitals, and three partners contributed data on visits to emergency departments and urgent care clinics. The analysis included adults age 50 years and older with Covid-19-like symptoms who underwent molecular testing for SARS-CoV-2 during the study period.

Researcher Mark G. Thompson, PhD, and colleagues with the CDC’s Covid-19 Response Team assessed 41,552 admissions to hospitals and 21,522 visits to 221 emergency departments or urgent care clinics during the period from January 1 through June 22, 2021.

Covid-19 vaccination status was documented in electronic health records and immunization registries, and the researchers 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 Jan. 1, 2021, to the index date for each medical visit), and local virus circulation.

The analysis revealed:

  • The effectiveness of full vaccination with two doses of an mRNA vaccine was 89% (95% CI, 87-91) against laboratory-confirmed SARS-CoV-2 infection leading to hospitalization, 90% (95% CI, 85-93) against infection leading to an ICU admission, and 91% (95% CI, 89-93) 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 among the BNT162b2 and mRNA-1273 vaccines and ranged from 81% to 95% in adults 85 years of age or older, people with chronic medical conditions, and Black or Hispanic adults.
  • The effectiveness of the Johnson & Johnson single shot Ad26.COV2.S vaccine was 68% (95% CI, 50-79) against laboratory confirmed SARS-CoV-2 infection leading to hospitalization and 73% (95% CI, 59-82) against infection leading to an emergency department or urgent care clinic visit.
Study limitations cited by the researchers included the possibility of unmeasured and residual confounders, the fact that the percentage of patients tested for SARS-CoV-2 by molecular assay differed across network partners, and the possible misclassification of vaccine exposures or outcomes.
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In addition, the researchers were unable to evaluate vaccine effectiveness against specific variants of concern that emerged during the study.

Despite these and other limitations, the data indicated high vaccine efficacy in the age group most at risk for severe Covid-19 and death from the disease, Thompson and colleagues concluded.

“These findings reinforce the value of widespread Covid-19 vaccination, underscore the importance of completing vaccination for both mRNA-based vaccines, and may help to motivate persons who remain hesitant to be vaccinated, including Black adults and Hispanic adults,” the researchers wrote.

  1. Full vaccination with either the Pfizer-BioNTech or Moderna mRNA vaccine was found by CDC investigators to be 91% effective against lab-confirmed Covid-19 leading to an emergency department or urgent care visit and 89% effective against infection leading to hospitalization.

  2. Vaccination with the single-dose Johnson & Johnson Ad26.COV2.S vaccine was found to be 73% effective against confirmed Covid-19 leading to an emergency department or urgent care visit and 68% effective against hospitalization due to SARS-CoV-2 infection.

Salynn Boyles, Contributing Writer, BreakingMED™

This research was funded by the U.S. Centers for Disease Control and Prevention.

Mark Thompson and the other CDC researchers reported no relevant disclosures related to this study.

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