BACKGROUND AND PURPOSE: 

• Tenforde et al. (JAMA, 2021) evaluated whether COVID-19 vaccination attenuates disease severity for those with breakthrough infections 

METHODS: 

• Case-control analysis 
  • 21 US hospitals  
• Participants 
  • Adults hospitalized between March and August, 2021 
  • 28-day outcome data on death and mechanical ventilation available 
• Exposures 
  • COVID-19 vaccination 
• Study design 
  • For hospitalization analysis 
    • Case patients: Those with COVID-19 
    • Controls: Those hospitalized for an alternative diagnosis 
  • For disease progression analysis 
    • Case patients: COVID-19 patients with progression to death or mechanical ventilation 
    • Controls: COVID-19 patients without progression 
  • Associations were measured with multivariable logistic regression 
• Primary outcomes 
  • Hospitalization for COVID-19 
  • Disease progression among those hospitalized 

RESULTS: 

• Case patients (COVID-19 patients): 1983 | Controls: 2530 
  • Median (IQR) age 59 (45 to 69) years; 48.8% women 
  • 23.0% non-Hispanic Black individuals | 15.9% Hispanic individuals 
  • 20.1% with an immunocompromising condition 
• Unvaccinated patients accounted for 84.2% of COVID-19 hospitalizations 
• Hospitalization for COVID-19 was significantly associated with decreased likelihood of vaccination  
  • Cases (COVID-19): 15.8% vaccinated 
  • Controls (other indications): 54.8% vaccinated  
  • aOR 0.15 (95% CI, 0.13 to 0.18) 
• This included patients with both SARS-CoV-2 Alpha and Delta variants 
  • Alpha 
    • Cases (COVID-19): 8.7% vaccinated 
    • Controls (other indications): 51.7% vaccinated 
    • aOR 0.10 (95% CI, 0.06 to 0.16) 
  • Delta 
    • Cases (COVID-19): 21.9% vaccinated 
    • Controls (other indications): 61.8% vaccinated 
    • aOR 0.14 (95% CI, 0.10 to 0.21) 
• Association with vaccination status was stronger for immunocompetent patients vs immunocompromised patients (P<0.001) 
  • Immunocompetent 
    • Cases (COVID-19): 11.2% vaccinated 
    • Controls (other indications): 53.5% vaccinated 
    • aOR 0.10 (95% CI, 0.09 to 0.13) 
  • Immunocompromised 
    • Cases (COVID-19): 40.1% vaccinated 
    • Controls (other indications): 58.8% vaccinated 
    • aOR 0.49 (95% CI, 0.35 to 0.69) 
• The association was weaker at more than 120 days since vaccination with Pfizer vs Moderna (P<0.001) 
  • Pfizer 
    • Cases (COVID-19): 5.8% vaccinated 
    • Controls (other indications): 11.5% vaccinated 
    • aOR 0.36 (95% CI, 0.27 to 0.49) 
  • Moderna 
    • Cases (COVID-19): 1.9% vaccinated 
    • Controls (other indications): 8.3% vaccinated 
    • aOR 0.15 (95% CI, 0.09 to 0.23) 
• Among the 1197 patients hospitalized with COVID-19, death or invasive mechanical ventilation by day 28 was associated with decreased likelihood of vaccination 
  • Cases: 12.0% vaccinated 
  • Controls: 24.7% vaccinated 
  • aOR 0.33 (95% CI, 0.19 to 0.58) 

CONCLUSION: 

• mRNA-based COVID-19 vaccination was less likely among hospitalized patients with COVID-19 vs patients hospitalized for other conditions 
• Death and mechanical ventilation were also associated with a decreased likelihood of vaccination among those hospitalized 
• The authors state 

These findings are consistent with risk reduction of developing severe COVID-19 among patients with vaccine breakthrough infections compared with absence of vaccination 

Learn More – Primary Sources: 

Association Between mRNA Vaccination and COVID-19 Hospitalization and Disease Severity 

Related ObG Topics:

Breakthrough COVID-19 Following Vaccination: What are the Risk Factors?

How does Vaccination Impact Viral Load and Duration of Illness in Those with Breakthrough SARS-CoV-2 Infection?

Real World Data: COVID-19 Vaccination and Reduction in Risk for Reinfection