Resurgence of SARS-CoV-2 Infection in a Highly Vaccinated Health System Workforce


In a recent letter to the editor of the New England Journal of Medicine, SARS-CoV-2 infections in healthcare workers at the University of California San Diego Health (UCSDH) are reported to coincide with the end of California's mask mandate and the rapid dominance of the B.1.617.2 (Delta) variant, and accounted for over 95% of UCSDH isolates by the end of July. Between 1 March 31 July, 227 healthcare workers tested positive for SARS-CoV-2 by PCR assay; of these, 130 (57.3%) were fully vaccinated, and symptoms were present in 109 (83.8%) of these. Of the 90 unvaccinated individuals, 80 (88.9%) exhibited symptoms.   

Of workers in the UCSDH system, 83.1% have been vaccinated with an mRNA vaccine (Pfizer-BioNTech or Moderna). In July, the case rate for symptomatic SARS-CoV-2 infection among vaccinated individuals was 5.7 per 1,000 individuals and 16.3 per 1,000 among unvaccinated individuals, indicating a vaccine effectiveness of 65.5%. Compared with the month of June, which had a vaccine efficacy rate of 94.3%, there was a 30% decline in effectiveness. The dramatic change in vaccine effectiveness from June to July is likely due to the emergence of the Delta variant and waning immunity over time, compounded by the end of masking requirements in California and the resulting increased risk of exposure in the community. 

Source: Keehner J, Horton LE, Binkin NJ, et al. Resurgence of SARS-CoV-2 Infection in a Highly Vaccinated Health System Workforce.  2021/09/01, New England Journal of Medicine. DOI: 10.1056/NEJMc 2112 981.

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