According to data presented at the recent American College of Rheumatology (ACR) Convergence 2023 Meeting, obtaining a fourth COVID mRNA vaccine decreased the risk of developing a severe COVID-19 infection by 65% in patients with systemic autoimmune rheumatic diseases who used immunomodulators.

The authors wrote, “Many patients with systemic autoimmune rheumatic diseases (SARDs) using immunomodulators have blunted humoral responses to COVID-19 vaccines. As such, the initial mRNA vaccine series is defined as three doses for this population, and a 4th (or first “booster”) dose was recommended by the CDC in October 2021. However, 4th dose uptake among patients with SARDs has been low. In the general population, a 4th vaccine dose reduces the risk of breakthrough infection; its effectiveness in SARDs receiving immunomodulators has not been established.”

To investigate the effectiveness of a fourth COVID-19 vaccine dose in patients with systemic autoimmune rheumatic diseases who are using immunomodulators, researchers conducted an “emulated target trial” in an extensive U.S. healthcare system.

The study comprised 4,010 participants diagnosed with a systemic autoimmune rheumatic disease who were also taking immunomodulating drugs. The most common treatments were conventional synthetic disease-modifying antirheumatic drugs (DMARDs; 58%) and biologic DMARDs (39%). Before the third dose, 599 (14.9%) had a previous COVID-19 infection.

Between January 16, 2022, and June 11, 2022, the trial included 4,010 patients who received three or more mRNA vaccines and were eligible for a fourth dose during the study period; of this group, 2,994 patients received a fourth dose and 1,014 did not.

The primary outcome was COVID-19 infection (positive COVID-19 polymerase chain reaction or antigen test or positive COVID-19 flag in the electronic record). The researchers indicated, “Follow-up ended at the earliest of (1) COVID-19; (2) bivalent vaccine availability (9/1/22); (3) “deviation” from the assigned arm (i.e., 5th dose for cases, 4th dose for comparators); (4) or non-COVID death as a competing risk.”

Employing logistic regression, the propensity score (PS) for receiving the fourth dose was calculated weekly, and researchers conducted time-stratified, overlap PS–weighted Cox regressions to assess the correlation of the fourth dose to the risk of each outcome.

According to the researchers, the incidence of COVID-19 infection in the fourth-dose group was 14.8 cases per 1,000 person-months, compared with 23.7 per 1,000 person-months among comparators. This resulted in a rate difference between the two cohorts of –8.85 (95% CI, –13.37 to –4.33) and a hazard ratio [HR] of 0.59 (95% CI, 0.47-0.74) per 1,000 person-months favoring the vaccination group.

The results also revealed that individuals in the fourth dose group were also less prone to experience hospitalization or mortality due to COVID-19 within 14 days of infection—0.36 versus 0.93 events per 1,000 person-months (HR = 0.35; 95% CI, 0.14-0.85).

Based on their findings, the researchers concluded that during the Omicron era, a fourth dose of mRNA vaccine diminished the risk of COVID-19 by 41% and severe COVID-19 by 65% among patients with SARDs using immunomodulators. Additionally, the authors noted that patients with SARDs should be encouraged to receive at least four doses of mRNA vaccines.

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