COVID-19: Illness After Vaccination

Important updates regarding our data

In the course of our regularly scheduled data updates, the DHS Surveillance team identified a system performance issue resulting in a lag in data being processed into our system. We are actively working with our vendor to resolve this issue, but in the meantime our reported data may appear artificially low. We plan to provide an update once the issue has been resolved.

Jump to specific COVID-19 chart on this page:

 

The COVID-19 vaccines are extremely effective at preventing serious illness, hospitalization, and death. Fully vaccinated people who test positive for COVID-19 more than 2 weeks after their completed vaccine dose series are called "breakthrough infections." No vaccine is 100 percent effective, and as such we expect to see some fully vaccinated people test positive for COVID-19. Breakthrough cases typically report mild illness or no symptoms.

Your likelihood of being infected with the virus that causes COVID-19 is determined by many factors, which include vaccinations, but also include the level of transmission and vaccine coverage in your community, whether you or others wear masks as recommended, the number of people you have close contact with, and more. On average, fully vaccinated individuals are less likely to be infected, hospitalized, and die from COVID-19 compared to unvaccinated individuals.

DHS plans to update this data by the 15th of every month. This data is updated on a monthly basis, halfway through the following month, to account for the 2-week data lag in receiving COVID-19 reports and to ensure the most complete data is presented for the previous, full month.

 

 

Understanding our data: What does this chart mean?

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This visualization shows the age-adjusted rate of confirmed and probable COVID-19 cases, hospitalizations, and deaths per 100,000 people among fully vaccinated people in Wisconsin for the last full month. Viewing case, death, and hospitalization rates allows the two groups to be compared directly while accounting for differences in population size across groups. The population denominator used to calculate rates is adjusted monthly based on the number of residents who completed the COVID-19 vaccine series.

The above rates are age-adjusted. Age adjustment, or age standardization, is used in epidemiology to allow populations to be compared directly when the age distribution of who most commonly gets the disease, or seriously sick from the disease, is skewed. Almost all diseases or health outcomes occur at different rates in different age groups, and that is true of COVID-19. Older populations are, in general, more likely to experience severe illness and death due to COVID-19.

In the case of the COVID-19 vaccine, older populations were eligible to receive the vaccine before younger populations. As such, they represent a larger proportion of the fully vaccinated population. On the other hand, younger populations represent a larger proportion of the not fully vaccinated group. In order to more fairly compare rates of hospitalization and death among fully vaccinated and not fully vaccinated groups, we do an age adjustment so that the overall rates are based on the same population proportions. This is similar to calculating a rate per 100,000 in order to compare rates across populations of different sizes.

Please note: Data on whether or not a confirmed or probable case of COVID-19 is hospitalized is not always complete in WEDSS. As such, the true rate of hospitalization among the fully vaccinated and not fully vaccinated groups may differ slightly from what is presented here.

About our data: How do we measure this?

Data source: The Wisconsin Immunization Registry (WIR) and Wisconsin Electronic Disease Surveillance System (WEDSS).

Read our Frequently Asked Questions for more information on how cases of COVID-19 are reported in WEDSS.

Fully vaccinated people who test positive for COVID-19 more than 2 weeks after their completed vaccine dose series are called breakthrough infections. Breakthrough infections shown in the data only include those that meet the Centers for Disease Control (CDC) vaccine breakthrough infection definition. We identify vaccine breakthrough infections by comparing immunization records in WIR to confirmed and probable case records in WEDSS. This allows us to match person records between COVID-19 cases and vaccination status. The non-fully-vaccinated population includes individuals who:

  • Have no COVID-19 vaccine doses reported in WIR.
  • Have an incomplete COVID-19 vaccine series reported in WIR.
  • Are within the two-week window after completing their COVID-19 vaccine series required to build full immunity.

We plan to update our data by the 15th of each month.

Back to a list of charts on this page.


Understanding our data: What does this chart mean?

This chart shows the crude rate of confirmed and probable cases, deaths, and hospitalizations per 100,000 amongst fully vaccinated and not fully vaccinated people by age group for the last month. The crude rate shows the rate based on the total number of incidences in that age group out of the total age group population multiplied by 100,000. The chart also displays the age-adjusted rates for fully vaccinated and not fully vaccinated people to the right of the chart.

Age adjustment, or age standardization, is used in epidemiology to allow populations to be compared directly when the age distribution of who most commonly gets the disease, or seriously sick from the disease, is skewed. Almost all diseases or health outcomes occur at different rates in different age groups, and that is true of COVID-19. Older populations are, in general, more likely to experience severe illness and death due to COVID-19.

In the case of the COVID-19 vaccine, older populations were eligible to receive the vaccine before younger populations. As such, they represent a larger proportion of the fully vaccinated population. On the other hand, younger populations represent a larger proportion of the not fully vaccinated group. In order to more fairly compare rates of hospitalization and death among fully vaccinated and not fully vaccinated groups, we do an age adjustment so that the overall rates are based on the same population proportions. This is similar to calculating a rate per 100,000 in order to compare rates across populations of different sizes.

Viewing case, death, and hospitalization data as rates allows the two groups to be compared directly while accounting for differences in population size across groups, especially as the proportion of fully vaccinated people increases.

Please note: Data on whether or not a confirmed or probable case of COVID-19 is hospitalized is not always complete in WEDSS. As such, the true rate of hospitalization among the fully vaccinated and not fully vaccinated groups may differ slightly from what is presented here.

About our data: How do we measure this?

Data source: The Wisconsin Immunization Registry (WIR) and Wisconsin Electronic Disease Surveillance System (WEDSS).

Read our Frequently Asked Questions for more information on how cases of COVID-19 are reported in WEDSS.

Fully vaccinated people who test positive for COVID-19 more than 2 weeks after their completed vaccine dose series are called breakthrough infections. Breakthrough infections shown in the data only include those that meet the Centers for Disease Control (CDC) vaccine breakthrough infection definition. We identify vaccine breakthrough infections by comparing immunization records in WIR to confirmed and probable case records in WEDSS. This allows us to match person records between COVID-19 cases and vaccination status. The non-fully-vaccinated population includes individuals who: 

  • Have no COVID-19 vaccine doses reported in WIR.
  • Have an incomplete COVID-19 vaccine series reported in WIR.
  • Are within the two-week window after completing their COVID-19 vaccine series required to build full immunity.

We plan to update our data by the 15th of each month.

Back to a list of charts on this page.


Understanding our data: What does this chart mean?

This chart shows the crude rate of confirmed and probable cases, deaths, and hospitalizations per 100,000 amongst fully vaccinated and not fully vaccinated people by month. The crude rate shows the rate based on the total number of incidences in that month out of the total population multiplied by 100,000. It also displays the percent of the population who completed their COVID-19 vaccine series by the first of the month for added context on how our statewide vaccination efforts have progressed. Viewing case, death, and hospitalization data as rates allows the two groups to be compared directly while accounting for differences in population size across groups, especially as the proportion of fully vaccinated people increases. 

Please note: Data on whether or not a confirmed or probable case of COVID-19 is hospitalized is not always complete in WEDSS. As such, the true rate of hospitalization among the fully vaccinated and not fully vaccinated groups may differ slightly from what is presented here.

About our data: How do we measure this?

Data source: The Wisconsin Immunization Registry (WIR) and Wisconsin Electronic Disease Surveillance System (WEDSS).

Read our Frequently Asked Questions for more information on how cases of COVID-19 are reported in WEDSS.

Fully vaccinated people who test positive for COVID-19 more than 2 weeks after their completed vaccine dose series are called breakthrough infections. Breakthrough infections shown in the data only include those that meet the Centers for Disease Control (CDC) vaccine breakthrough infection definition. We identify vaccine breakthrough infections by comparing immunization records in WIR to confirmed and probable case records in WEDSS. This allows us to match person records between COVID-19 cases and vaccination status. The non-fully-vaccinated population includes individuals who: 

  • Have no COVID-19 vaccine doses reported in WIR.
  • Have an incomplete COVID-19 vaccine series reported in WIR.
  • Are within the two-week window after completing their COVID-19 vaccine series required to build full immunity.

We plan to update our data by the 15th of each month.

Back to a list of charts on this page.


How can I download DHS COVID-19 data?

All DHS COVID-19 data is available for download directly from the chart on the page. You can click on the chart and then click "Download" at the bottom of the chart (gray bar).

To download our data visit one of the following links:

Updated Data*

Data dictionary

*As of May 27, 2021, the visualizations are using an updated data file that allows corrections due to quality assurance to be counted on the date when a case or death was first reported, rather than affecting the current daily count of cases or deaths.

You can find more instructions on how to download COVID-19 data or access archived spatial data by visiting our FAQ page


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Last Revised: September 15, 2021

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