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.
Between January 1, 2021 and September 7, 2021 in Pennsylvania, 97% of COVID-19-related deaths were in unvaccinated or not fully vaccinated people.
- Among a total of 6,472 COVID-19-related deaths identified in Pennsylvania in 2021, there were at least 213 post-vaccination deaths identified (3%).
- Cumulative death incidence among the unvaccinated and not fully vaccinated was 7.9 times as high as the death incidence among the fully vaccinated (56 vs 7 per 100,000).
Between January 1, 2021 and September 6, 2021 in Pennsylvania, 95% of reported hospitalizations with COVID-19 as the primary diagnosis / cause of admission were in unvaccinated or not fully vaccinated people.
- Among a total of 34,468 hospitalizations with COVID-19 as the primary diagnosis / cause of admission reported in Pennsylvania, 1,820 were reported to have occurred in fully-vaccinated Pennsylvanians. These figures account for data from 55% of all hospitals and 69% of acute care hospitals in Pennsylvania.
Between January 1, 2021 and September 7, 2021 in Pennsylvania, 94% of reported COVID-19 cases were in unvaccinated or not fully vaccinated people.
- Among a total of 639,729 positive cases, there have been 35,389 identified post-vaccination cases (6%).
- Cumulative case incidence among the unvaccinated and not fully vaccinated was 7.1 times as high as the case incidence among the fully vaccinated (5,840 vs. 819 per 100,000).
- 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 PADOHand 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 hospitalizations with COVID-19 as the primary diagnosis / cause of admission and for each vaccination status, (2) that the total number of hospitalizations 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) that the sum of the hospitalized patients by vaccination status equaled the reported total number of hospitalizations with COVID-19 as the primary diagnosis / cause of admission.
- 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.