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Staff at a Southern California hospital system experienced a small resurgence of coronavirus infections this summer, although more than four-fifths of its workers have been fully vaccinated.
The findings join a flurry of recent reports of so-called “breakthrough” infections in those vaccinated. Earlier this summer, Provincetown, Massachusetts, reported an outbreak of Covid among many vaccinated residents, and the Centers for Disease Control and Prevention confirmed that these cases occur more often with the highly contagious Delta variant of the virus than with the previous versions. .
Breakthrough infections tend to be mild, and vaccines are still very effective against severe disease and death of the Delta variant. Yet studies of breakthrough infections have fueled the debate over the need for a booster dose, which the Biden administration has supported, as well as masking requirements to prevent the spread of Delta.
Even among its fully vaccinated workers, the University of California at San Diego Health saw a significant increase in infections from June through July, according to a letter published Wednesday in the New England Journal of Medicine.
From March to July, a total of 227 workers tested positive, according to the letter. Of these, 130 – or 57% – were vaccinated.
The total number of symptomatic cases of Covid-19 has increased more than eight-fold, from 15 in June to 125 in July, with 75% of cases occurring in fully vaccinated employees.
No deaths have been reported and an unvaccinated person has been hospitalized, the researchers say.
While the number of cases represented a tiny fraction of the overall 19,000 workforce at the University of California at San Diego Health, the growing number of infections indicates a noticeable drop in vaccine effectiveness, the authors say. .
“Our data suggest that vaccine efficacy against any symptomatic disease is significantly lower against the delta variant and may decline over time after vaccination,” they wrote.
Given these results, they recommended a swift return to indoor masking and intensive testing strategies to detect the virus.
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