key: cord-1029528-54fmvcl5
authors: Lan, F.-Y.; Sidossis, A.; Iliaki, E.; Buley, J.; Nathan, N.; Bruno-Murtha, L. A.; Kales, S. N.
title: Continued Effectiveness of COVID-19 Vaccination among Urban Healthcare Workers during Delta Variant Predominance
date: 2021-11-16
journal: nan
DOI: 10.1101/2021.11.15.21265753
sha: dbeb5b6bf96d4dfe0117682bbae03c072a6fb028
doc_id: 1029528
cord_uid: 54fmvcl5

Background: Data on COVID-19 vaccine effectiveness (VE) among healthcare workers (HCWs) during periods of delta variant predominance are limited. Methods: We followed a population of urban Massachusetts HCWs (45% non-White) subject to epidemiologic surveillance. We accounted for covariates such as demographics and community background infection incidence, as well as information bias regarding COVID-19 diagnosis and vaccination status. Results and Discussion: During the study period (December 16, 2020 to September 30, 2021), 4615 HCWs contributed to a total of 1,152,486 person-days at risk (excluding 309 HCWs with prior infection) and had a COVID-19 incidence rate of 5.2/10,000 (114 infections out of 219,842 person-days) for unvaccinated person-days and 0.6/10,000 (49 infections out of 830,084 person-days) for fully vaccinated person-days, resulting in an adjusted VE of 82.3% (95% CI: 75.1-87.4%). For the secondary analysis limited to the period of delta variant predominance in Massachusetts (i.e., July 1 to September 30, 2021), we observed an adjusted VE of 76.5% (95% CI: 40.9-90.6%). Independently, we found no re-infection among those with prior COVID-19, contributing to 74,557 re-infection-free person-days, adding to the evidence base for the robustness of naturally acquired immunity.

(114 infections out of 219,842 person-days) for unvaccinated person-days and 0.6/10,000 (49 infections out of 830,084 person-days) for fully vaccinated person-days, resulting in an adjusted VE of 82.3% (95% CI: 75.1-87.4%). For the secondary analysis limited to the period of delta variant predominance in Massachusetts (i.e., July 1 to September 30, 2021), we observed an adjusted VE of 76.5% (95% CI: 40.9-90.6%). Independently, we found no re-infection among those with prior COVID-19, contributing to 74,557 re-infection-free person-days, adding to the evidence base for the robustness of naturally acquired immunity.

. CC-BY 4.0 International license It is made available under a is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity. (which was not certified by peer review) preprint other potential determinants of infection rates is even more scarce.

To investigate the continued effectiveness of COVID-19 vaccination during the Delta variant predominance in a diverse and urban healthcare setting.

A community-based healthcare system in Massachusetts runs a COVID-19 vaccination program for employees (described previously (1) . CC-BY 4.0 International license It is made available under a is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity. (which was not certified by peer review) preprint

The copyright holder for this this version posted November 16, 2021. ; https://doi.org/10.1101/2021.11.15.21265753 doi: medRxiv preprint

We followed all actively serving HCWs in the system from December 16, 2020 to September 30, 2021, excluding those with prior COVID-19 infection from the main analyses. The outcome was having a positive PCR assay during the study period documented by the healthcare system's Occupational Health department (2) . The established master database, comprised of workers' demographics, prior infection, de novo PCR positivity, vaccination (validated by the Massachusetts Immunization Information System and/or the healthcare system's medical records), and human resource administrative data, has been previously described (1, 2) . For each HCW, we calculated the person-days at risk and categorized them according to vaccination status. A HCW's follow-up person-days were censored at the end of the study period, his/her termination date, the date tested positive for COVID, or the date he/she received a 3rd vaccine dose , whichever came first.

The Andersen-Gill extension of the Cox proportional hazards models were built to account for correlated data. We further adjusted for age, sex, race, and the Massachusetts statewide 7-day average of tested COVID cases (3) on the date the first dose was given to control for background rates. We estimated VE by calculating 100%×(1−hazard ratio). The R software (version 3.6.3) was used for statistical . CC-BY 4.0 International license It is made available under a is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity. (which was not certified by peer review) preprint Figure) .

We further conducted a secondary analysis limiting the study period from July 1, 2021 to September 30, 2021, corresponding to delta variant predominance in Massachusetts (4). We observed an incidence rate of 5.8/10,000 (15 events out of 25,910 person-days) for unvaccinated person-days and 1.3/10,000 (39 events out of 308,267 person-days) for 14 days after fully vaccinated, resulting in an adjusted VE of 76.5% (95% CI: 40.9-90.6%).

. CC-BY 4.0 International license It is made available under a is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity. (which was not certified by peer review) preprint

The copyright holder for this this version posted November 16, 2021. ; https://doi.org/10.1101/2021.11.15.21265753 doi: medRxiv preprint When we examined HCWs (n=423) with infections occurring before vaccination, no re-infection was observed, accumulating 74,557 re-infection-free person-days (starting 10 days after initial infection and censoring at the date of receiving their first vaccine dose). Further, after vaccination, previously infected HCWs did not contribute any breakthrough infection events among the vaccinated HCWs.

To our knowledge, this study is one of the first in healthcare settings regarding continued VE during delta variant predominance. Our work also provides further evidence of naturally acquired immunity. We found similar VE against the delta variant, 76%, compared to another study's findings, 66% (5). Strengths included accounting for covariates and information bias such as demographics and background incidence, a multiethnic study population, consistent COVID-19 screening criteria, and well-validated vaccination records. Nonetheless, we did not examine individual manufacturers' VE due to a limited power.

. CC-BY 4.0 International license It is made available under a is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity. (which was not certified by peer review) preprint

The copyright holder for this this version posted November 16, 2021. ; https://doi.org/10.1101/2021.11.15.21265753 doi: medRxiv preprint

COVID-19 vaccine efficacy in a diverse urban healthcare worker population. medRxiv. Preprint posted online 6

COVID-19 symptoms predictive of healthcare workers' SARS-CoV-2 PCR results

Archive of COVID-19 cases in Massachusetts

Outbreak of SARS-CoV-2 infections, including COVID-19 vaccine breakthrough infections

Effectiveness of COVID-19 vaccines in preventing SARS-CoV-2 infection among frontline workers before and during B.1.617.2 (Delta) variant predominance -Eight

It is made available under a is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity. (which was not certified by peer review) preprint Vaccine effectiveness (95% CI) derived from the Andersen-Gill extension of the Cox proportional hazards model * Adjust for age, sex, race, and the Massachusetts statewide 7-day average of new tested COVID-19 cases at the date for the first vaccine dose. Those with the race of "American Indian or Alaska Native", "Hawaiian or Pacific Islander", or "Two or More" were pooled into one level "other race". † Not eligible for those receiving J&J/Janssen ‡ Equal or more than 14 days after single dose of J&J/Janssen or having received the second shot of Pfizer or Moderna . CC-BY 4.0 International license It is made available under a is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity. is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity. (which was not certified by peer review) preprintThe copyright holder for this this version posted November 16, 2021. ; https://doi.org/10.1101/2021.11.15.21265753 doi: medRxiv preprint