A 3-dose series of the mRNA-1273 COVID-19 vaccine was more effective at preventing infection and severe outcomes than the 2-dose series in immunocompromised individuals, according to study results published in Vaccine.

Researchers conducted a matched cohort study at Kaiser Permanente Southern California (KPSC) to analyze the relative vaccine effectiveness of the 3-dose mRNA-1273 primary series COVID-19 vaccine among immunocompromised. Patients (N=43,884) were randomly assigned 1:1 to receive either 2- or 3-dose mRNA-1273 primary series vaccination. The groups were matched by age, sex, race/ethnicity, and the administration date of the second vaccine dose. The primary outcomes were COVID-19 infection and severe COVID-19 infection. Cumulative incidence rates (IR) of COVID-19 infection and severe COVID-19 infection were determined via the Kaplan-Meier method and compared between the groups via log-rank testing.

Among patients included in the analysis, the median age was 65 (IQR, 54-74) years, 51% were women, and 47% were non-Hispanic White. There were more stem cell and solid organ transplant recipients in the 3- vs 2-dose groups (10.1% vs 5.9%). Patients in the 3-dose group also had higher Charlson comorbidity index scores and received more preventive care within the previous year.

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The incidence of COVID-19 infection per 1000 person-years was higher among patients in the 2-dose group (IR, 478.9; 95% CI, 449.6-510.1) vs those in the 3-dose group (IR, 277.9; 95% CI, 263.1-293.4). The incidences (per 1000 py) of COVID-19-related hospitalization (IR, 42.5; 95% CI, 34.5-52.4 vs IR, 16.1; 95% CI, 12.8-20.1) and in-hospital mortality (IR, 2.9; 95% CI, 1.3-6.4 vs IR, 0.4; 95% CI, 0.1-1.7) were also higher among 2-dose recipients.

In the adjusted analysis, the relative vaccine effectiveness (rVE) of 3- vs 2-dose primary series mRNA-1273 vaccination for protection against COVID-19 infection, hospitalization, and in-hospital mortality was 55%, 83%, and 87.1%, respectively.

“[T]he higher rVE [relative vaccine effectiveness] of the 3-dose vaccination series did not persist long-term for this population,” the researchers noted.

Study limitations include the observational design, potentially misclassified COVID-19 diagnoses, and the lack of data on relative vaccine effectiveness against specific COVID-19 variants.

According to the researchers “These findings underscore the importance of immunocompromised patients completing the 3-dose primary series and support recommendations for a booster (fourth) dose for additional protection against SARS-CoV-2 infection and severe COVID-19 outcomes.”

Disclosures: This research was supported by Moderna, Inc. Multiple study authors declared affiliations with biotech, pharmaceutical, and/or device companies. Please see the original reference for a full list of authors’ disclosures.

This article originally appeared on Infectious Disease Advisor