Monitoring Incidence of COVID-19 Cases, Hospitalizations, and Deaths, by Vaccination Status - 13 U.S. Jurisdictions,...

Area of Science:

• Epidemiology
• Infectious Diseases
• Vaccinology

Background:

• COVID-19 vaccine breakthrough infections are monitored to understand disease trends in vaccinated individuals.
• The emergence of highly transmissible variants like SARS-CoV-2 Delta necessitates ongoing surveillance.
• Vaccine effectiveness (VE) studies are crucial for assessing protection against infection and severe outcomes.

Purpose of the Study:

• To analyze COVID-19 incidence, hospitalization, and death rates by vaccination status during the rise of the Delta variant.
• To assess potential changes in vaccine protection against SARS-CoV-2 infection and severe COVID-19.
• To evaluate the utility of breakthrough infection surveillance for early detection of waning vaccine immunity.

Main Methods:

• Analysis of reported COVID-19 cases, hospitalizations, and deaths in adults across 13 U.S. jurisdictions.
• Linking of case surveillance data with immunization registry data.
• Calculation of age-standardized incidence rate ratios (IRRs) comparing unvaccinated to fully vaccinated persons during periods of low and high Delta variant prevalence.

Main Results:

• Incidence rate ratios for cases decreased from 11.1 to 4.6 as Delta variant prevalence increased.
• Incidence rate ratios for hospitalizations decreased from 13.3 to 10.4.
• Incidence rate ratios for deaths decreased from 16.6 to 11.3.
• Findings suggest a potential decline in vaccine protection against infection but continued strong protection against hospitalization and death.

Conclusions:

• COVID-19 vaccination provides strong protection against severe illness and death, even with the Delta variant.
• Surveillance of breakthrough infections may signal changes in vaccine effectiveness.
• Continued monitoring and VE studies are essential for public health decision-making.