Resurgence of SARS-CoV-2 Infection in the Workforce of Highly Vaccinated Health Systems

September 1, 2021

DOI: 10.1056 / NEJMc2112981

Commentary

In December 2020, the University of California, San Diego Health (UCSDH) reported experiencing a dramatic increase in severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infections.

And mRNA vaccination began in mid-December 2020, with 76% fully vaccinated by March, rising to 87% by July.

As a result, infections were dramatically reduced by early February 2021, with fewer than 30 health care workers testing positive each month. However, with the end of the California masking mandate on June 15, and from mid-April to the end of July, the rapid transmission of the B.1.617.2 (delta) variant, which accounted for more than 95% of UCSDH isolates, was confirmed and shown to be increasing, even including cases among those who had been fully immunized.

Therefore, ethics committee approval was obtained for the use of administrative and case study data on vaccination to investigate the efficacy of the mRNA SARS CoV-2 vaccine in the study.

The threshold for the UCSDH SARS-CoV-2 test is low and is triggered by the presence of at least one symptom or identified exposure during daily screening, regardless of vaccination status.

From March 1, 2021 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.

Of the 227 workers, 130 (57.3%) were fully vaccinated and symptoms were present in 109 (83.8%) of the 130 fully vaccinated workers and 80 (88.9%) of the 90 unvaccinated workers. No deaths were reported in either group.

Vaccine efficacy was calculated for each month from March to July, and cases were defined as one or more symptoms in people who had a positive PCR test and had not been previously infected with Covid-19.

The results 

show that the vaccine efficacy exceeded 90% from March to June, but declined to 65.5% in July.

The July case rate was analyzed according to the month in which the Covid-19 workers completed the series of vaccinations: the incidence rate for workers who completed the vaccination in January or February was 6.7 per 1,000, while the incidence rate for those who completed the vaccination was 3.7 per 1,000.

The July incidence rate among the unvaccinated was 16.4 per 1,000.

The SARS CoV-2 mRNA vaccines, BNT162b2 (Pfizer-BioNTech) and mRNA-1273 (Moderna), showed efficacy rates of 95% and 94.1%2 respectively in the first clinical trial.

4 months after the second dose, the efficacy decreased slightly (84%) but appears to persist with the BNT162b2 vaccine.

In the United Kingdom, where extended dosing intervals of up to 12 weeks were used, vaccine efficacy was reported to be maintained at 88% against symptomatic disease associated with delta variants, and as observed by others in the population vaccinated with mRNA vaccine according to the standard emergency licensed interval, these data suggest that vaccine efficacy against symptomatic disease is considerably lower against delta variants and may wane with time since vaccination.