Effectiveness of a mRNA vaccine booster dose against COVID-19 among Oregon health care personnel, January 2021 to June 2023.

Background: The prioritization of US health care personnel (HCP) for early receipt of messenger RNA (mRNA) vaccines against SARS-CoV-2 allowed for the evaluation of the effectiveness of these vaccines in a real-world setting among a high-risk population. This study aimed to summarize the sociodemographic characteristics of eligible HCP in Oregon and estimate vaccine effectiveness (VE) of a mRNA COVID-19 vaccine booster dose.

Methods: Using a case-control design, we compared HCP with positive antigen or nucleic acid amplification test SARS-CoV-2 test results (cases) to those with negative results (controls) and matched by site and test date. Using conditional logistic regression adjusted for age, sex, race and ethnicity, educational level, underlying conditions, and exposure to COVID-19, we estimated VE for a third COVID-19 vaccine booster dose using the screening method as 1-odds ratio × 100%.

Results: VE of a mRNA booster dose was 62.6% (95% CI: 37.6%, 77.6%), compared with 2-dose primary mRNA vaccination. Additionally, HCP with a college degree (vs no degree), private insurance (vs government), and an income level $200K+ (vs < $50K) were more likely to have received the booster vaccine.

Conclusions: The mRNA COVID-19 booster vaccine conferred approximately 63% protection against COVID-19 among Oregon HCP. These findings encourage remaining up-to-date with subsequent COVID-19 vaccines.