COVID-19 Resurgence Identified in Highly Vaccinated Healthcare Staff

The New England Journal of Medicine published the findings from a Correspondence today based on the University of California San Diego Health (UCSDH) workforce experienced with SARS-CoV-2 virus infections.

On September 1, 2021, this Letter to the Editor revealed UCSDH's workforce experienced a dramatic increase in SARS-CoV-2 infections.

Vaccination with mRNA vaccines began in mid-December 2020, and by March 2021, 76% of the workforce had been fully vaccinated.

As planned, SARS-CoV-2 infections decreased dramatically by early February 2021.

Between March and June, fewer than 30 health care workers tested positive for the coronavirus each month.

Furthermore, the percentage of USCDH's fully vaccinated staff had risen to 83% by July.

However, mRNA vaccine effectiveness exceeded 90% until June, then fell to 65.5% in July.

No vaccine effectiveness data for August 2021 was disclosed in this Letter.

July case rates were analyzed according to the month in which workers with Covid-19 completed the vaccination series. For example, in workers completing vaccination in January or February, the attack rate was 6.7 per 1000 persons (95% CI, 5.9 to 7.8).

Whereas the attack rate was 3.7 per 1000 persons (95% CI, 2.5 to 5.7) among those who completed vaccination from March through May.

Among unvaccinated persons, the July virus attack rate was 16.4 per 1000 persons (95% CI, 11.8 to 22.9).

'The dramatic change in vaccine effectiveness from June to July is likely to be due to both the emergence of the Delta variant (90%) and waning vaccine immunity over time, compounded by the end of masking requirements in California and the resulting greater risk of exposure in the community,' wrote these researchers.

'Our findings underline the importance of rapidly reinstating nonpharmaceutical interventions, such as indoor masking and intensive testing strategies, in addition to continued efforts to increase vaccinations, as strategies to prevent avoidable illness and deaths and to avoid mass disruptions to society during the spread of this formidable variant.'

'Furthermore, if our findings on mRNA vaccine waning immunity are verified in other settings, booster doses may be indicated.'

Note: Institutional review board approval was obtained for the use of administrative data on vaccinations and case-investigation data to examine mRNA vaccine effectiveness. The mRNA vaccines, Comirnaty (Pfizer–BioNTech) and SpikeVax (Moderna) have previously shown efficacy rates of 95% and 94.1%,2 respectively, in earlier clinical trials.