COVID-19 surges among vaccinated health care workers
SAN DIEGO, U.S.: Administrative data from University of California San Diego Health (UCSDH) shows that, between June and July, a rapid increase occurred in symptomatic SARS-CoV-2 infections in fully vaccinated health care workers. In a letter to the New England Journal of Medicine, UCSDH doctors said that the surge appeared to show the effects of waning immunity compounded by relaxed health measures and the spread of the more transmissible delta (B.1.617.2) variant in California.
The letter explained that an increase in SARS-CoV-2 infections within the UCSDH workforce was recorded in December 2020—the same month that vaccination of the workforce using mRNA vaccines began. By the end of March, 76.3% of the 18,964-strong workforce had been fully vaccinated using vaccines made by Moderna and Pfizer-BioNTech. Infection rates had dropped by mid-February 2021, and during April and May, fewer than 30 cases of symptomatic SARS-CoV-2 infection were recorded within the workforce per month. However, a rapid increase in symptomatic infections was recorded in July among fully vaccinated staff.
The administrative data showed that cases of symptomatic infection among vaccinated staff jumped from three in May and five in June to 94 in July. Within the unvaccinated portion of the workforce (which accounted for 13.7% staff in June), symptomatic infection increased from ten in May and June to 31 in July.
“From March 1 to July 31, 2021, a total of 227 UCSDH health care workers tested positive for SARS-CoV-2 by reverse-transcriptase–quantitative polymerase-chain-reaction (RT-qPCR) assay of nasal swabs; 130 of the 227 workers (57.3%) were fully vaccinated. Symptoms were present in 109 of the 130 fully vaccinated workers (83.8%) and in 80 of the 90 unvaccinated workers (88.9%),” the letter read.
“[If] our findings on waning immunity are verified in other settings, booster doses may be indicated”
UCSDH staff calculated vaccine effectiveness within the workforce and said that it exceeded 90% from March through June but fell to 65.5% in July. The data suggested that the effectiveness of mRNA vaccines given at standard emergency use authorization intervals against symptomatic infection is lower against the delta variant and may wane over time, the authors wrote.
“The dramatic change in vaccine effectiveness from June to July is likely to be due to both the emergence of the delta variant and waning immunity over time, compounded by the end of masking requirements in California and the resulting greater risk of exposure in the community,” the authors explained.
They added: “[If] our findings on waning immunity are verified in other settings, booster doses may be indicated.”
The letter, titled “Resurgence of SARS-CoV-2 infection in a highly vaccinated health system workforce,” was published online on Sept. 1, 2021, in the New England Journal of Medicine, ahead of inclusion in an issue, and can be accessed here.