Skip to Main Content

Evaluating SARS-CoV-2 Vaccine Effectiveness among Healthcare Personnel during Early Phase Vaccination


The development of a safe and effective vaccine against SARS-CoV-2 (COVID-19) was a monumental turning point in the COVID-19 pandemic. Beginning in mid-December 2020, healthcare personnel (HCP) were among the first to receive these vaccines because of their increased risk of contracting SARS-CoV-2 from interactions with infected patients and their vital work caring for those critically ill during the pandemic. Clinical trials of SARS-CoV-2 vaccines showed high efficacy, but it is essential to evaluate vaccine effectiveness soon after introduction of a vaccine to assess real-world experience and inform any revision of vaccine recommendations. The early phase distribution of vaccines provided an opportunity to evaluate effectiveness in preventing symptomatic COVID-19 among a high-exposure population. This project continues to give insight into how these vaccines work in a real-world setting with changing variants, booster recommendations, and updated vaccines. Enrollment for this project has concluded but analyses are ongoing.

Goals & Objectives

  1. Evaluate post-introduction effectiveness of a complete schedule of the SARS-CoV-2 vaccine in preventing laboratory-confirmed symptomatic COVID-19 among HCP.
  2. Evaluate post-introduction effectiveness of the SARS-CoV-2 vaccine in preventing severe disease among HCP with laboratory-confirmed symptomatic COVID-19.
  3. Evaluate effectiveness by HCP age groups and in subgroups with comorbidities.
  4. Evaluate effectiveness by various groups of HCP job categories and clinical practice settings.
  5. Evaluate effectiveness by vaccine product, number of doses, and bivalent booster product.


This activity is being conducted at 10 Emerging Infections Program (EIP) sites in the United States. In Connecticut, the evaluation of the SARS-CoV-2 vaccine among healthcare personnel (HCP) began January 1, 2021. Healthcare facilities participating in this project include hospitals and outpatient services of a large health system located in Connecticut. Yale EIP staff work with health system staff to identify HCP tested for SARS-CoV-2. HCP who test positive (cases) and negative (controls) for SARS-CoV-2 who agree to be contacted are interviewed to collect vaccination history, demographics, underlying medical conditions, roles in healthcare facilities, locations of work in the healthcare facility, possible community exposures, and PPE used during COVID-19 patient care.

Data stripped of personal identifiers was shared with each participating facility as well as aggregated and shared with CDC for further analysis. Enrollment for this project has concluded but analyses are ongoing.


Plumb ID, Briggs Hagen M, Wiegand R, et al. Effectiveness of a bivalent mRNA vaccine dose against symptomatic SARS-CoV-2 infection among U.S. Healthcare personnel, September 2022–May 2023. Vaccine. Published online November 14, 2023. doi:10.1016/j.vaccine.2023.10.072

Plumb ID, Mohr NM, Hagen M, et al. Effectiveness of a Messenger RNA Vaccine Booster Dose Against Coronavirus Disease 2019 Among US Healthcare Personnel, October 2021–July 2022. Open Forum Infectious Diseases. 2023;10(10):ofad457. doi:10.1093/ofid/ofad457

Pilishvili T, Gierke R, Fleming-Dutra KE, et al. Effectiveness of mRNA Covid-19 Vaccine among U.S. Health Care Personnel. New England Journal of Medicine. 2021;385(25):e90. doi:10.1056/NEJMoa2106599

Pilishvili T, Fleming-Dutra KE, Farrar JL, et al. Interim Estimates of Vaccine Effectiveness of Pfizer-BioNTech and Moderna COVID-19 Vaccines Among Health Care Personnel — 33 U.S. Sites, January–March 2021. MMWR Morb Mortal Wkly Rep. 2021;70(20):753-758. doi:10.15585/mmwr.mm7020e2

Project Contact

Adeline Morris, MPH

Epidemiologist 2
Connecticut Emerging Infections Program
One Church Street, 7th Floor
New Haven, CT 06510
(203) 737-3694