Risk factors for breakthrough SARS-CoV-2 infection in vaccinated healthcare workers.

BACKGROUND AND OBJECTIVE: The risk factors for breakthrough infections among healthcare workers (HCW) after completion of a full course of vaccination are poorly understood. Our objective was to determine the risk factors for breakthrough SARS-CoV-2 infection among HCWs at a national healthcare system in Qatar. METHODS: We identified all HCWs at Hamad Medical Corporation in Qatar between December 20, 2020 and May 18, 2021 with confirmed SARS-CoV-2 RT-PCR infection >14 days after the second vaccine dose. For each case thus identified, we identified one control with a negative test after December 20, 2020, matched on age, sex, nationality, job family and date of SARS-CoV-2 testing. We excluded those with a prior positive test and temporary workers. We used Cox regression analysis to determine factors associated with breakthrough infection. RESULTS: Among 22,247 fully vaccinated HCW, we identified 164 HCW who had breakthrough infection and matched them to 164 controls to determine the factors associated with SARS-CoV-2 breakthrough infection. In the breakthrough infection group the nursing and midwifery job family constituted the largest group, spouse was identified as the most common positive contact followed by a patient. Exposure to a confirmed case, presence of symptoms and all other job families except Allied Health Professionals when compared with nursing and Midwifery staff independently predicted infection. CONCLUSION: Presence of symptoms and contact with a confirmed case are major risk factors for breakthrough SARS-CoV-2 infection after vaccination, and these groups should be prioritized for screening even after full vaccination.

Prevalence and risk factors for SARS-CoV-2 infection and seroprevalence among clinical and non-clinical staff in a national healthcare system.

BACKGROUND: While many studies have reported the rate and risk of SARS-CoV-2 infection among healthcare workers (HCWs), there are scant data regarding the impact of employment type and job grades upon such risk. METHODS: We determined the rate of SARS-CoV-2 infection based on a positive nasopharyngeal swab (NPS) PCR among employees of a large national healthcare system. Antibody testing was performed on those who agreed to provide a blood sample. Using logistic regression analysis, we determined the risk of infection (PCR+) associated with demographic characteristics, job family and job grade. RESULTS: We identified 35,075 staff (30,849 full-time, 4,226 outsourced) between March 1-October 31, 2020. Among full-time employees, 78.0% had a NPS (11.8% positive). Among outsourced staff, 94.4% had a NPS (31.1% positive). Antibody testing was performed on 33.9% full-time employees (13.0% reactive), and on 39.1% of the outsourced staff (47.0% reactive). PCR-positivity was higher among outsourced staff (31.0% vs. 18.3% in non-clinical and 9.0% in clinical full-time employees) and those in the low-grade vs. mid-grade and high-grade job categories. Male sex (OR 1.88), non-clinical job family (OR 1.21), low-grade job category (OR 3.71) and being an outsourced staff (OR 2.09) were associated with a higher risk of infection. CONCLUSION: HCWs are a diverse population with varying risk of infection. Clinical staff are at a lower risk likely due to increased awareness and infection prevention measures. Risk is higher for those in the lower socioeconomic strata. Infection is more likely to occur in non-healthcare setting than within the healthcare facilities.