SARS-CoV-2 Infection in Public School District Employees Following a District-wide Vaccination Program

Philadelphia County, Pennsylvania, March 21-April 23, 2021

David Rubin, MD; Maggie Eisen, MSS; Sophia Collins, MSN; Jeffrey W. Pennington, MSCS; Xi Wang, PhD; Susan Coffin, MD


Morbidity and Mortality Weekly Report. 2021;70(30):1040-1043. 

In This Article

Abstract and Introduction


The School District of Philadelphia reopened for in-school instruction the week of March 21, 2021, and required weekly testing for SARS-CoV-2, the virus that causes COVID-19, for all employees returning to in-school responsibilities. The resumption of in-school instruction followed a mass vaccination program using the Pfizer-BioNTech 2-dose vaccine offered under a partnership between the Philadelphia Department of Public Health and Children's Hospital of Philadelphia to all 22,808 School District of Philadelphia employees during February 23–April 3, 2021.* The subsequent mandatory testing program provided an opportunity to assess the percentage of positive BinaxNow point-of-care antigen tests (Abbott Laboratories) identified among school staff members based on their self-reported vaccination status (i.e., received zero, 1, or 2 vaccine doses) at the time of testing. During the initial 5 weeks after schools reopened, 34,048 screening tests were performed. Overall, 0.70% of tests returned a positive result. The percentage of positive test results was lower among persons who reported receipt of 2 vaccine doses (0.09%) compared with those who reported receipt of 1 dose (1.21%) or zero doses (1.76%) (p<0.001) representing a 95% reduction in percentage of positive SARS-CoV-2 test results among persons reporting receipt of 2 compared with zero doses of Pfizer-BioNTech vaccine. Vaccination of school staff members has been highlighted as an important strategy to maximize the safety of in-person education of K–12 students this fall.[1] These findings reinforce the importance of promoting COVID-19 vaccination among school staff members before commencement of the 2021–22 school year.

The School District of Philadelphia provided a roster of all school staff members who were invited to participate in the February 23–April 3 vaccination program. The roster included employee age, sex, and race; ethnicity of employees was not provided by the school district but was self-reported at the time of vaccination. School-based testing of all School District of Philadelphia staff members working within the district's buildings, including those who did and did not have regular contact with students, was launched the week of March 21, 2021; mandatory weekly screening testing programs were conducted by trained nurses and designated staff members using point-of-care antigen tests. All persons reported the presence or absence of symptoms at the time of testing. Both symptomatic and asymptomatic persons who received a positive SARS-CoV-2 test result were excluded from work and required to self-isolate; asymptomatic persons were also encouraged to undergo confirmatory testing using a nucleic acid amplification test; however, no data on testing conducted outside of this school-based testing program was reported. Antigen test results were automatically reported through the secure mobile application PARapidTest (Southwest Texas Regional Advisory Council [STRAC]) to Pennsylvania's National Electronic Disease Surveillance System.

Deidentified data were analyzed to determine the percentage of SARS-CoV-2 positive test results among staff members who did not report recent exposure to a symptomatic or asymptomatic person infected with SARS-CoV-2, overall and by vaccination status. Exposure history was obtained from responses to questions asked of staff members before testing. Self-reported vaccination status was collected at the time of testing and included vaccine doses received through the county school vaccination program as well as outside the program. Because only 2-dose COVID mRNA vaccines were authorized for use by the Food and Drug Administration at the time of the study, vaccination status was categorized by self-reported number of doses of vaccine received (i.e., zero, 1, or 2 doses) at the time of testing. Information was not collected on whether ≥2 weeks had passed since receipt of the second dose, so some persons who had received 2 vaccine doses might not have been optimally protected at the time of testing.

Available data were used to calculate the percentages of staff members who were vaccinated through the program as of April 3, 2021, overall, and within each demographic group. Chi-square tests were performed to determine whether vaccination coverage of school staff members differed by demographic characteristics. Results of all school-based testing conducted during March 21–April 23, 2021, were used to calculate the percentage of asymptomatic persons with positive test results, overall and by vaccination status. Risk ratios (RRs) comparing vaccinated with unvaccinated groups were calculated. Statistical significance was set at α = 0.05 for all comparisons. All analyses were conducted using SAS software (version 9.4; SAS Institute). All data collection and analysis for the School District of Philadelphia vaccination and screening testing programs were in accordance with the authorities of local public health jurisdictions for emergency public health response activities and received a nonresearch determination.

Among 22,808 district employees eligible for COVID-19 vaccination, 10,700 (46.9%) received ≥1 dose through the program; 46.1% of staff members received both doses of vaccine through the program (Table 1). Approximately one half (51.9%) of eligible staff members aged 40–65 years were vaccinated through the program; coverage was 44.5% among persons aged 17–39 years and 27.9% among those aged >65 years. The highest coverage with ≥1 dose (95.1%) was among Asian or Pacific Islander persons, followed by White persons (65.3%). Approximately one third (32.6%) of Black or African American persons received ≥1 dose through the program. Coverage was higher among Hispanic or Latino persons (52.1%) than among persons of other ethnic groups (46.6%) and was similar among men and women.

During March 21–April 23, the weekly number of tests performed increased from 6,215 to 12,232. By April 23, 54% of 22,808 school staff members, representing persons on-site for work responsibilities and including persons both with and without symptoms, had received 34,048 tests (Table 2), 238 (0.70%) of which were positive for SARS-CoV-2. In total, 21,083 (62%) tests were performed for persons reporting receipt of 2 vaccine doses, 1,737 (5.1%) for persons reporting receipt of 1 dose, and 11,228 (33.0%) for those who had received zero doses. Among 2-dose, 1-dose, and zero-dose vaccine recipients, 0.09%, 1.21%, and 1.76% of test results, respectively, were positive (p<0.001), representing a 95% lower percentage of positive test results among staff members who received 2 doses compared with those who were unvaccinated (RR = 0.04; 95% confidence interval [CI] = 0.02–0.07). Among staff members who did not report symptoms at the time of testing, the percentage of positive tests was lower among persons who received both vaccine doses (0.09%) than among those who had received 1 dose (0.82%) or zero doses (1.22%) (p<0.001), representing a 93% reduction in percentage of positive test results among asymptomatic school staff members who had received 2, versus zero, vaccine doses (RR = 0.07; 95% CI = 0.04–0.11). Compared with zero-dose recipients, the percentage of positive test results was 31% lower among all 1-dose recipients and 33% lower among asymptomatic 1-dose recipients; however, the differences were not statistically significant between these two groups.

*The mass vaccination program was the principal opportunity offered within the county for school employees in the region to receive COVID-19 vaccine. Some persons aged >65 years or with chronic conditions might have obtained vaccines available to Philadelphia residents through these other priority designations, although supply at that time was scarce.
The application did not track serial testing of individual persons, although persons who received positive test results were not retested in subsequent weeks during this study period.