Correspondence

More on SARS-CoV-2 Infection after Vaccination in Health Care Workers

To the Editor

Keehner and colleagues (May 6 issue)1 reported on SARS-CoV-2 infection among California health care workers during the vaccination campaign from December 16, 2020, through February 9, 2021. The SARS-CoV-2 positivity rate decreased over time after vaccine administration. The authors correlated this trend with the efficacy of the vaccines in preventing SARS-CoV-2 infection. In our opinion, the positivity rate should also be correlated with the regional trend in SARS-CoV-2 infection. In the California population, the daily number of new cases of infection reached its peak at the beginning of January and then rapidly decreased to values nearly 20 times lower in mid-February.2 This frank reduction is similar to the trend observed by the authors among vaccinated health care workers in the same period. Moreover, as of February 9, 2021, less than 10% of the California population had received at least one dose of vaccine and less than 5% were fully vaccinated.2 We suggest that the analysis be extended over time to ascertain the efficacy of the vaccination campaign against the spread of SARS-CoV-2 infection.

Alberto Tosoni, M.D.
Fondazione Policlinico Universitario Agostino Gemelli, Rome, Italy

Antonio Mirijello, M.D.
Casa Sollievo della Sofferenza, San Giovanni Rotondo, Italy

Giovanni Addolorato, M.D.
Fondazione Policlinico Universitario Agostino Gemelli, Rome, Italy

No potential conflict of interest relevant to this letter was reported.

This letter was published on May 12, 2021, at NEJM.org.

  1. 1. Keehner J, Horton LE, Pfeffer MA, et al. SARS-CoV-2 infection after vaccination in health care workers in California. N Engl J Med 2021;384:1774-1775.

  2. 2. COVID19.CA.gov. Tracking COVID-19 in California. (https://covid19.ca.gov/state-dashboard/).

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Response

Cases of SARS-CoV-2 Infection in San Diego County and among Health Care Workers at UCSD Health.

The bar graph shows the incidence of SARS-CoV-2 infection among health care workers in the University of California at San Diego (UCSD) health system, and the curve indicates the rolling 7-day mean incidence in the general population of San Diego County.

The authors reply: Tosoni et al. suggest that we correlate positive SARS-CoV-2 test results with regional trends over a longer follow-up period. Our original letter described a pooled data set from the health systems at the University of California at San Diego (UCSD) and the University of California at Los Angeles, where surges were slightly asynchronous.1 Unlike the intense testing strategy used for health care workers, tests were performed only for symptomatic persons in the general population of the county. At UCSD Health, we are able to track SARS-CoV-2 tests among vaccinated and unvaccinated health care workers. Cases of SARS-CoV-2 infection among health care workers peaked early in January and rapidly declined by the week of January 10, at which point cases peaked in the general population of San Diego County (Figure 1).1 Furthermore, from January 15 onward, when 70% of health care workers had received a first vaccine, 37% of positive test results among health care workers were among those who had been vaccinated and 63% were among those who had not been vaccinated. This supports the notion that vaccine-induced immunity was starting in vaccinated health care workers.2 We advocate for rapid vaccination of all eligible persons to quickly and safely achieve herd immunity, mitigate regional surges, and decrease the risk of sustained transmission and the evolution of new more transmissible and deadlier variants.3,4

Jocelyn Keehner, M.D.
Shira R. Abeles, M.D.
Francesca J. Torriani, M.D.
UC San Diego Health, San Diego, CA

Since publication of their letter, the authors report no further potential conflict of interest.

This letter was published on May 12, 2021, at NEJM.org.

  1. 1. New cases by day: positive COVID-19 cases in San Diego County, from August 1, 2020. San Diego Union-Tribune. 2021 (https://www.sandiegouniontribune.com/tracking-coronavirus-cases-san-diego-county).

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  2. 2. Thompson MG, Burgess JL, Naleway AL, et al. Interim estimates of vaccine effectiveness of BNT162b2 and mRNA-1273 COVID-19 vaccines in preventing SARS-CoV-2 infection among health care personnel, first responders, and other essential and frontline workers eight U.S. locations, December 2020CMarch 2021. MMWR Morb Mortal Wkly Rep 2021;70:495-500.

  3. 3. Longhurst CA, Kremer B, Maysent PS. Rapid implementation of a vaccination superstation. JAMA 2021;325:931-932.

  4. 4. Centers for Disease Control and Prevention. COVID data tracker: variant proportions. 2021 (https://www.cdc.gov/coronavirus/2019-ncov/cases-updates/variant-proportions.html).

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