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Home » Reduced COVID-19 risk in healthcare workers after vaccines – real-world evidence

Reduced COVID-19 risk in healthcare workers after vaccines – real-world evidence

Three new articles published in the New England Journal of Medicine provided powerful evidence of reduced risk of COVID-19 in healthcare workers who received one or more vaccinations against the disease. Health care workers have a much higher exposure to COVID-19 than the average person, so this kind of data is extremely interesting.

I have written in the past about challenge studies, where the subjects are intentionally exposed to SARS-CoV-2 after receiving the vaccines. Many people, including myself, think they are unethical. However, healthcare workers, who are unintentionally exposed to the virus, function as a “challenge study” in that those who are vaccinated do not have to “wait” for an infection, it’s going to happen eventually.

It is also important to note that these healthcare workers are more frequently tested for the virus than the average person on the street. This alone makes the data even more intriguing.

These three articles describe the level of reduced COVID-19 risk after being vaccinated in a healthcare setting. The results should convince anyone that the vaccine is very effective.

Photo by Manuel Chinchilla on Unsplash

Reduced COVID-19 risk in vaccinated groups

The three articles published as “letters” (Seen Note 1) in the New England Journal of Medicine (NEJM) provided data on the risk of contracting COVID-19 among healthcare workers in three settings:

All three articles examined the risk of COVID-19 in both vaccinated and unvaccinated groups of healthcare workers and other employees at these healthcare systems. Let’s take a look at the data for each of the healthcare systems:

  • UCLA and UCSD – Out of 36,659 eligible employees, the rate of COVID-19 infection was 2.5% of those tested within the first week after the first dose, 1.2% during the second week, 0.7% in the third week, 0.4% during the week after the second dose was given, and less than 0.2% in the second week after the second dose. In other words, the risk of infection dropped by over 95% within two weeks after receiving the second dose of either the Moderna or Pfizer vaccines.
  • UTSW – Out of 23,234 eligible employees, 2.61 % of nonvaccinated employees, 1.82% of partially vaccinated employees, and 0.05% of fully vaccinated employees contracted COVID-19. The authors observed a greater than 90% decrease in the number of employees who are either in isolation or quarantine due to COVID-19.
  • HHUMC – The incidence of COVID-19 positive tests in vaccinated individuals dropped from about 0.7% during the two weeks post-vaccination to nearly 0% within 5 weeks.


The authors of the California studies concluded:

The rarity of positive test results 14 days after administration of the second dose of vaccine is encouraging and suggests that the efficacy of these vaccines is maintained outside the trial setting. These data underscore the critical importance of continued public health mitigation measures (masking, physical distancing, daily symptom screening, and regular testing), even in environments with a high incidence of vaccination, until herd immunity is reached at large.

The authors of the UTSW study concluded:

Real-world experience with SARS-CoV-2 vaccination at UTSW has shown a marked reduction in the incidence of infections among employees. This decrease has preserved the workforce when it was most needed.

Finally, the authors of the HHUMC study concluded:

These findings suggest that widespread and effective vaccination among health care workers provides a safe environment, even in the presence of a high rate of SARS-CoV-2 infection in the community.

These are all preliminary studies, lacking complex statistical analyses and descriptions of methods, but they represent powerful evidence of the effectiveness of the vaccines. If vaccinated healthcare workers, who are constantly “challenged” by the SARS-CoV-2 virus, have much lower risks of the disease, those of us who are not at the frontline of this disease should feel good about being protected.

reduced COVID-19 risk
Photo by Branimir Balogović on Unsplash


  1. “Letters” in most peer-reviewed journals are essentially letters to the editor, except, in this case, it is a method to rapidly communicate new data and information. This is a step above the preprint servers, but not quite at the level of a published, peer-reviewed article. NEJM is highly respected and has very high standards for reviewing these letters, so these three “letters” provide substantive evidence of the reduced risk of COVID-19 in healthcare workers.


Michael Simpson

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