Although the risk is low, infection is possible after the COVID-19 vaccine

In a letter to New England Journal of Medicine, published online March 23, 2021, a group of researchers from the University of California San Diego School of Medicine and UCLA’s David Geffen School of Medicine report COVID-19 infection rates for a group of health care workers who received the previous vaccine for the novel coronavirus.

“Because of the mandatory daily symptom screening of health care workers, patients, and visitors, and the high testing capacity of both UC San Diego Health and UCLA Health, we were able to identify symbolic and asymptomatic diseases in the among health care workers at our centers, “said co – author Jocelyn Keehner MD, an infectious disease partner at UC San Diego School of Medicine.

“Furthermore, we were able to report infection rates in a real world situation, where vaccine distribution coincided with an increase in disease. We saw a low detection rate among those who have been vaccinated. vaccinated health care workers, supporting high levels of protection of these vaccines. ”

The authors looked at collected data from UC San Diego and UCLA healthcare workers who received either the Pfizer or Moderna vaccines between December 16, 2020 and February 9, 2021 (36,659 first doses, 28,184 second doses), time which was followed by a significant increase in COVID-19 infections in the region.

Within this group, 379 people tested positive for SARS-CoV-2 at least one day after receiving the vaccine, with the majority (71 percent) testing positive for SARS-CoV-2. within the first two weeks after the first dose. Thirty-seven health care workers tested positive after receiving two doses, which is when the two vaccines are expected to achieve maximum protection.

The authors estimated that the overall risk for a positive test for SARS-CoV-2 after vaccination for health care workers at UC San Diego Health was 1.19 percent and 0.97 percent at UCLA Health, both higher than the risk identified in Moderna and Pfizer clinical trials, which were not limited to health care workers.

“There are several possible explanations for this elevated risk,” said co-author Lucy E. Horton, MD, MPH, associate professor in the Department of Infectious Diseases and Global Public Health at UC San Diego School of Medicine and director medical UC UC San Diego Health Information Management Unit.

“First, the health care workers surveyed have access to regular asymptomatic and symptomatic testing. Second, there was a regional increase in infections over vaccination interventions during this period. third, there are differences in the demographics of health care workers compared to participants in the vaccine clinical trials.Healthcare workers tend to be younger and at greater risk of being exposed to SARS- CoV-2 in the community. “

High levels of disease have been strongly associated with behaviors that increase risk of being seen, such as attending social gatherings in restaurants and bars without adequate concealment. and doing physical speed. This connection is more strongly associated with younger age demographics.

In addition, well-known co-author Michael A. Pfeffer, MD, assistant vice chancellor and chief information officer at UCLA Health, Moderna and Pfizer clinical trials ceased to collect data prior to the December-February increase and many without an asymptomatic test were performed.

The authors found that the risk of infection 14 days after the second dose, when the maximum immunity is expected to be reached, was very rare. “It suggests that the effectiveness of these vaccines is kept out of the test setting,” they wrote.

However, they also noted that the risk is zero. While both Pfizer and Moderna report efficiency levels in the mid-90s, neither is 100 percent.

“It emphasizes the importance of public health mitigation measures (shelter, physical pace, daily symptom screening and regular testing), even in high-vaccination environments, to achieve general herd protection,” said the co-author. -responsible Francesca Torriani, MD, professor of clinical medicine in the Department of Infectious Diseases and Global Public Health at the UC San Diego School of Medicine and program director of Disease Prevention and Clinical Epidemiology at UC San Diego Health.


Additional co-authors include: Christopher A. Longhurst, Robert T. Schooley and Shira R. Abeles (co-author), all members of UC San Diego’s COVID-19 action group, and Judith S. Currier, UCLA.

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