COVID-19 Vaccine Effectiveness

Vaccines are the most effective tool we have right now to bring the COVID-19 pandemic under control. Risk of infection, hospitalization, and death are all much lower in people who are vaccinated compared to those who are not. However, no vaccine is 100% effective, and it is expected that some people will become infected even if they are vaccinated. 

This page displays the weekly rates of COVID-19 cases, hospitalizations, and deaths among unvaccinated, fully vaccinated but not boosted, and fully vaccinated and boosted Chicagoans. The filters on the graphic can be used to display the overall age-adjusted rates or rates by different age groups.

Data are updated on Wednesdays at 5:30 p.m. The Centers for Disease Control and Prevention (CDC) also studies COVID-19 vaccine effectiveness on the national level, data available here.

Data Source: Illinois' National Electronic Disease Surveillance System (I-NEDSS), Illinois Comprehensive Automated Immunization Registry Exchange (I-CARE), U.S. Census Bureau American Community Survey


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Dataset location and further description: https://data.cityofchicago.org/Health-Human-Services/COVID-19-Outcomes-by-Vaccination-Status/6irb-gasv

Rates for fully vaccinated and unvaccinated begin the week ending April 3, 2021 when COVID-19 vaccines became widely available in Chicago. Rates for boosted begin the week ending October 23, 2021 after booster shots were recommended by the Centers for Disease Control and Prevention (CDC) for adults 65+ years old and adults in certain populations and high risk occupational and institutional settings who received Pfizer or Moderna for their primary series or anyone who received the Johnson & Johnson vaccine.

Vaccination status:

  • Fully vaccinated: Completion of primary series of a U.S. Food and Drug Administration (FDA)-authorized or approved COVID-19 vaccine at least 14 days prior to a positive test (with no other positive tests in the previous 45 days).
  • Boosted: Fully vaccinated with an additional or booster dose of any FDA-authorized or approved COVID-19 vaccine received at least 14 days prior to a positive test (with no other positive tests in the previous 45 days).
  • Unvaccinated: No evidence of having received a dose of an FDA-authorized or approved vaccine prior to a positive test.
  • CLARIFYING NOTE: Those who started but did not complete all recommended doses of an FDA-authorized or approved vaccine prior to a positive test (i.e., partially vaccinated) are excluded from this visual.

Outcomes:

  • Cases: People with a positive molecular (PCR) or antigen COVID-19 test result from an FDA-authorized COVID-19 test that was reported into I-NEDSS. A person can become re-infected with SARS-CoV-2 over time and so may be counted more than once in this dataset. Cases are counted by week the test specimen was collected.
  • Hospitalizations: COVID-19 cases who are hospitalized due to a documented COVID-19 related illness or who are admitted for any reason within 14 days of a positive SARS-CoV-2 test. Hospitalizations are counted by week of hospital admission.
  • Deaths: COVID-19 cases who died from COVID-19-related health complications as determined by vital records or a public health investigation. Deaths are counted by week of death.

Hospitalization data are delayed one week. Death data are delayed two weeks.

Incidence rates for fully vaccinated but not boosted people are calculated as total fully vaccinated but not boosted with outcome divided by cumulative fully vaccinated but not boosted at the end of each week. Incidence rates for boosted are calculated as total boosted with outcome divided by cumulative boosted at the end of each week. Incidence rates for unvaccinated are calculated as total unvaccinated with outcome divided by total population minus cumulative boosted, fully, and partially vaccinated at the end of each week. All rates are multiplied by 100,000.

Overall age-adjusted incidence rates and IRRs are standardized using the 2000 U.S. Census standard population. Rates by age group are crude rates.

Incidence rate ratios (IRRs) for the past eight weeks were calculated by dividing the cumulative unvaccinated rate by the cumulative vaccinated rate and by the cumulative boosted rate.

All data are provisional and subject to change. Information is updated as additional details are received and it is, in fact, very common for recent dates to be incomplete and to be updated as time goes on. This dataset reflects data known to CDPH at the time when the dataset is updated each week.

Numbers in this dataset may differ from other public sources due to when data are reported and how City of Chicago boundaries are defined.


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