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​Post-Vaccination Data

Updated 10/18/2021

The Pennsylvania Department of Health updated its report on COVID-19 post-vaccination events, commonly known as "breakthrough," showing that the vaccines continue to save lives and keep more people out of the hospital.

"What we continue to see is that the vaccines that are widely available to everyone 12 and older are highly effective for preventing hospitalizations and deaths, even as more post-vaccination cases occur in the context of more transmissible variants," Acting Secretary of Health Alison Beam said in releasing the latest Pennsylvania data as further evidence of the vaccines' effectiveness.

Acting Physician General Dr. Denise Johnson explained, "From a clinical perspective, we expect to see the number of breakthrough cases go up as more people get vaccinated. It is like what we saw with seat belt use years ago. As the number of people wearing seatbelts increased, the number of car accidents involving people wearing seatbelts went up. However, the overall fatality rate from car accidents dropped. Your chances of dying in a car accident drop dramatically if you wear a seatbelt. So too, your chances of dying from COVID-19 drop substantially if you are fully vaccinated."

This month's data shows that Pennsylvanians who are fully vaccinated fared much better than the unvaccinated even as the more infectious COVID-19 variant continues to dominate the nation.

In the past month, 74 percent of the 4,989 hospitalizations due to COVID-19 were among unvaccinated Pennsylvanians.

"That means that fully vaccinated people have a greater than three times better chance of staying out of the hospital due to COVID-19," Dr. Johnson said. "Another way to look at it, if you are playing the lottery and there is something you could do to triple your odds of hitting the jackpot, would you do it?"

"This is why doctors across the state want all of their eligible patients to get vaccinated," she said. "Vaccination substantially increases their odds of avoiding COVID-19 and staying out of the hospital where our healthcare workers are already overwhelmed."

Looking at the number of COVID-19 cases over the past 30 days shows that 74 percent of the 135,098 people who tested positive were unvaccinated. Data on the number of post-vaccination deaths in the past 30 days is not available due to a 60-day lag in the reporting and verification process.

"Reviewing this data over time helps inform our understanding of factors such as potential waning immunity," Dr. Johnson said. "This data is consistent with national trends and similar to data reviewed by the FDA and CDC resulting in a recommendation for a booster dose for vulnerable populations several months following the completion of the primary vaccination series."

What Is a Post-Vaccination COVID-19 Case?
Post-vaccination cases are defined as individuals who are fully vaccinated and became a confirmed or probable case of COVID-19 (i.e. had a positive PCR or antigen test for the SARS-CoV-2 virus) more than 14 days after they completed their full one-dose or two-dose COVID-19 vaccination series. They are also referred to as vaccine breakthrough cases.

What Is a Post-Vaccination COVID-19 Hospitalization?
Post-vaccination hospitalizations are COVID-19-related hospitalizations among individuals who were admitted withCOVID-19 as the primary diagnosis / cause for admission after they became fully vaccinated.

What Is a Post-Vaccination COVID-19 Death?
Post-vaccination deaths are a subset of the post-vaccination cases. Specifically, these are COVID-19-related deaths among individuals who became a confirmed or probable case of COVID-19 more than 14 days after they had completed their full one-dose or two-dose COVID-19 vaccination series. 

How Are Post-Vaccination COVID-19 Cases & Deaths Identified? 
The Pennsylvania Department of Health is identifying cases using COVID test results reported by Laboratories and healthcare providers. Post-vaccination cases are then identified by linking the disease surveillance registry (i.e. case data) to the immunization registry to find individuals who have an initial positive COVID-19 test at least 14 days after they have completed their full vaccination series. Occasionally vaccination information obtained from providers or from patient interviews is used if the case cannot be found in the vaccine registry. To identify deaths related to COVID-19, the department is also linking case data to the state death registry. COVID-19 deaths in persons determined to be post-vaccination cases are considered post-vaccination deaths.

How are Post-Vaccination COVID-19 Hospitalizations Identified?
The PA DOH collects both patient-level and aggregate hospitalization data by vaccination status from hospitals. Currently, the DOH is reporting valid, aggregate hospitalization and vaccination status data as self-reported by hospitals. DOH will continue to work with hospitals to improve the validity and completion of data submitted.

Why are we Tracking Post-Vaccination Events?
Tracking events of COVID-19 that occur after vaccination is important for monitoring public health. While COVID-19 vaccines are safe and effective, some cases, hospitalizations, and deaths are still expected in persons who have been vaccinated, as no vaccine is 100% effective.  If the incidence or severity of post-vaccination cases increases, this could be a signal of reduced protection against a variant.

What Is the Current Data on Post-Vaccination Events in Pennsylvania?
The data shows that the COVID-19 vaccines are highly effective for preventing hospitalizations and deaths, even as more post-vaccination cases occur in the context of more transmissible variants.

Deaths
Between January 1, 2021 and October 4, 2021 in Pennsylvania, 93% of COVID-19-related deaths were in unvaccinated or not fully vaccinated people.

  • Among a total of 7,625 COVID-19-related deaths identified in Pennsylvania in 2021, there were at least 518 post-vaccination deaths identified (7%).
  • Cumulative death incidence among the unvaccinated and not fully vaccinated was 6.0 times as high as the death incidence among the fully vaccinated (69 vs 12 per 100,000).

Hospitalizations
Between January 1, 2021 and October 4, 2021 in Pennsylvania, 93% of reported hospitalizations with COVID-19 as the primary diagnosis / cause of admission were in unvaccinated, not fully vaccinated, or unknown vaccination status individuals.

  • Among a total of 44,095 hospitalizations with COVID-19 as the primary diagnosis / cause of admission reported in Pennsylvania, 3,247 were reported to have occurred in fully-vaccinated Pennsylvanians (7%). These figures account for data from approximately 62% of all hospitals and 78% of acute care hospitals in Pennsylvania.
  • In the 28 days ending October 4, 2021, among a total of 4,989 hospitalizations with COVID-19 as the primary diagnosis / cause of admission, 1,287 were reported to have occurred in fully-vaccinated Pennsylvanians (26%).
  • In the 28 days ending October 4, 2021, the estimated cumulative hospitalization incidence among unvaccinated, not fully vaccinated, and unknown vaccination status individuals was 3.1 times as high as the estimated hospitalization incidence among the fully vaccinated (60 vs 19 per 100,000).
 
Cases
Between January 1, 2021 and October 4, 2021 in Pennsylvania, 91% of reported COVID-19 cases were in unvaccinated or not fully vaccinated people.
  • Among a total of 771,734 positive cases, there have been 69,822 identified post-vaccination cases (9%).
  • Cumulative case incidence among the unvaccinated and not fully vaccinated was 5.6 times as high as the case incidence among the fully vaccinated (7,456 vs. 1,328 per 100,000).
  • In the 30 days ending October 4, 2021, among a total of 135,098 positive cases, there were 34,609 identified post-vaccination cases (26%).
  • In the 30 days ending October 4, 2021, the cumulative case incidence among the unvaccinated and not fully vaccinated was 3.1 times as high as the case incidence among the fully vaccinated (1,633 vs. 520 per 100,000).

Technical Notes:

  • Vaccination counts were obtained from the two vaccine registries in Pennsylvania: SIIS (which collects information on vaccinations administered in PA outside of Philadelphia) and PhilaVax (the Philadelphia Department of Public Health [PDPH] vaccine registry).
    • For the SIIS data, we excluded out of state residents and persons with unknown address; and persons were not considered fully vaccinated until 14 days after they received the second of two doses of the Pfizer or Moderna vaccines or one dose of the Janssen vaccine.  Note that this differs from the PA Department of Health (PADOH) vaccine dashboard where the 14-day waiting period is not taken into account when calculating the percent fully covered.
    • The PhilaVax data was obtained from the PDPH'swebsite. We included both residents and non-residents of Philadelphia, as most non-residents probably reside in other PA counties rather than out-of-state.  As a result, some out-of-state residents may be included in the vaccination counts. The number of persons fully vaccinated displayed on the PDPH website also does not take the 14-day post-final vaccination waiting period into account. We were not able to adjust the PhilaVax data for the waiting period; as a result, the percent truly fully vaccinated may be slightly overestimated in this report.  The vaccination data for Philadelphia from PhilaVax was estimated from PDPH's website of cumulative weekly vaccination numbers. To estimate the daily number of PhilaVaxvaccinations, the difference between cumulative estimates for each week was calculated and each difference was divided by 7. The PhilaVax estimate for fully vaccinated individuals does not take into account the 14-day waiting period between the last dose of the vaccination and the vaccines effective date.  
  • COVID-19 case numbers were obtained from the PADOH and PDPH electronic reportable disease surveillance systems. Vaccine breakthrough cases were identified by matching vaccine registry data to case data submitted to the disease surveillance system, or from information obtained in a case investigation.
    • Persons with the same date of birth and the same or very similar first and last names in both the vaccine and case registries were considered to be the same person. Significant variations in name or data entry errors in name or date of birth may result in some vaccine breakthrough cases being missed. Results may change as matching strategies are refined over time.
    • The specimen collection date of the case's earliest positive COVID-19 PCR or antigen test was used as a proxy for the date of infection. As only one infection per individual is captured in this analysis, and that infection is the first infection, some vaccine breakthrough cases may be missed in those who have had COVID-19 more than once in 2021.
  • COVID-19-related deaths among COVID cases were identified by matching case data in our disease surveillance system to state death registry data, using probabilistic matching software.
    • The following COVID-19 deaths were not included: (1) deaths from the state death registry that did not match to the disease surveillance system due to data entry errors or significant variations in names, and (2) deaths in the state death registry that did not have a corresponding positive PCR or antigen test in the  disease surveillance system.
    • The state death registry determines if a death is COVID-related using criteria developed by the National Center for Health Statistics. Because it takes time for deaths to be reported, classified, and matched to case data, deaths may be lagged by about three weeks.
  • The number of prior-day hospitalizations with COVID-19 as the primary diagnosis / cause of admission, as well as patients' associated vaccination statuses, are self-reported by acute care hospitals into the Essential Elements of Information (EEI) data collection tool in CORVENA each day by 10am. Prior-day daily reporting of these data began on September 7, 2021. Each acute care hospital was also asked to report the total number of hospitalizations with COVID-19 as the primary diagnosis / cause of admission, as well as patients' associated vaccination statuses, for the period January 1, 2021 to September 6, 2021 through a survey distributed by the DOH in September 2021.
    • Only data that passed simple checks for validity is included in the final report. The validity checks ensure only that: (1) values were submitted for the total number of admissions with COVID-19 as the primary diagnosis / cause of admission and for each vaccination status, (2) the total number of admissions with COVID-19 as the primary diagnosis / cause of admission was not greater than the total number of patients confirmed to have COVID-19, and (3) the sum of the hospitalized patients by vaccination status equaled the reported total number of admissions with COVID-19 as the primary diagnosis / cause of admission.
    • In order to calculate the percentage of hospitals and acute care hospitals for which the hospitalization data accounts, the number of hospitals (or acute care hospitals) reporting valid data for the day according to the simple validity checks described above was divided by the total number of hospitals (or acute care hospitals) in PA. The reporting validity percentages of the cumulative report from January 1 to September 6 were used for each day in that period. The daily percentages of hospitals reporting valid data were then averaged over the full period beginning January 1, 2021.
    • The hospitalization rate should be considered a rough estimate.  It uses aggregate data reported by hospitals in PA.
    • Vaccination status in the hospitalization data is not able to be verified by matching to a vaccination registry and may represent self-reporting by the patient or patient's family.
    • People hospitalized with COVID-19 often need to be re-hospitalized.  The numerator of the hospitalization rate counts hospitalizations (thus double-counting persons hospitalized more than once), whereas the denominator counts persons, not hospitalizations.
    • Hospitalization incidence was estimated as follows: The count of admissions with COVID-19 as the primary diagnosis or cause of admission reported per day among fully vaccinated individuals was divided by the cumulative number of fully vaccinated persons as of the previous day, and the count of admissions with COVID-19 as the primary diagnosis or cause of admission reported per day among not fully vaccinated individuals and unknown vaccination status individuals was divided by the cumulative number of not fully vaccinated persons as of the previous day.   To obtain the cumulative hospitalization rate per 100,000 population, the daily incidence rates over the period were summed and then multiplied by 100,000.
    • Vaccination status in the hospitalization data is not able to be verified by matching to a vaccination registry and may represent self-reporting by the patient or patient's family.
    • Patient-level case and hospitalization data from NEDSS are not currently used for the hospitalization figures in this report. As such, when vaccination status of a hospitalized patient is unknown, they are included with not fully vaccinated.
  • The case incidence among the fully vaccinated population is expected to increase as vaccinated persons have more opportunities to be exposed to infectious persons, especially persons infected by more transmissible variants.  Case counts, population percentages and incidence calculations include all ages in PA, both adults and children.
    • Incidence rates were calculated as follows. The daily incidence rate for cases and deaths were calculated based on the COVID-19 infection count for the day divided by the cumulative number of fully vaccinated (or not-fully vaccinated) residents from the prior day. In this manner, only individuals who were fully vaccinated were included in the denominator. 
    • To obtain the cumulative incidence rate per 100,000 population, the sum was taken of the daily incidence rates over the period (past 30 days, or days since January 1, 2021) and multiplied by 100,000.