The effectiveness of up to three doses of COVID-19 vaccine was moderate overall and significantly lower among individuals with immunocompromising conditions, compared with the general population during the period of Omicron dominance, according to an analysis of data from more than 34,000 hospitalizations.
Previous studies have suggested lower COVID-19 vaccine effectiveness among immunocompromised individuals, compared with healthy individuals from the general population, but data from the period in which Omicron subvariants have been dominant are limited, wrote Amadea Britton, MD, of the Centers for Disease Control and Prevention’s COVID-19 Emergency Response Team, and colleagues.
The CDC currently recommends an expanded primary vaccine series of three doses of an mRNA vaccine, and the Advisory Committee on Immunization Practices has recommended a fourth dose with the new bivalent booster that contains elements of the Omicron variant, the researchers noted.
In a study published in the CDC’s Morbidity and Mortality Weekly Report, the researchers identified 34,220 adults with immunocompromising conditions who were hospitalized for COVID-19–like illness between Dec. 16, 2021, and Aug. 20, 2022. These conditions included solid malignancy (40.5%), hematologic malignancy (14.6%), rheumatologic or inflammatory disorder (24.4%), other intrinsic immune condition or immunodeficiency (38.5%), or organ or stem cell transplant (8.6%). They used data from the CDC’s VISION Network, a multistate database. The data include spring and summer 2022, when the BA.4 and BA.5 Omicron subvariants dominated other strains, and adults with immunocompromising conditions were eligible for a total of four vaccine doses (two primary doses and two boosters). The median age of the study population was 69 years, and 25.7%, 41.7%, and 7.0% had received two, three, and four doses, respectively, of COVID-19 vaccine.
Overall, vaccine effectiveness (VE) among immunocompromised patients was 34% after two vaccine doses, increasing to 71% during days 7-89 after a third dose, then declining to 41% 90 days or more after that dose.
During the full Omicron period, VE was 36% for 14 or more days after dose two, 69% for 7-89 days after dose three, and 44% for 90 or more days after dose three.
When VE was stratified by sublineage period, VE was higher 7 or more days after dose three during the predominance of BA.1 (67%), compared with VE during the dominant periods of BA.2/BA.2.12.1 (32%) and BA.4/BA.5 (35%).
In the later periods when Omicron BA.2/BA.2.12.1 and BA.4/BA.5 variants dominated, and individuals who had received three doses of vaccine were eligible for a fourth, VE against these variants was 32% 90 or more days after dose three and 43% 7 or more days after dose four.
VE was lowest among individuals with potentially more severe immunocompromising conditions, notably solid organ or stem cell transplants, the researchers wrote in their discussion.
The study findings were limited by several factors including the use of ICD-9 and -10 discharge diagnosis codes for immunocompromising conditions, potential confounding in VE models, lack of data on outpatient treatments such as nirmatelvir/ritonavir (Paxlovid), and lack of COVID-19 genomic sequencing data that may have affected which sublineage was identified, the researchers noted.
However, “this study confirms that even with boosters, immunocompromised adults, because of their weakened immune systems, are still at high risk of moderate to severe COVID,” said coauthor Brian Dixon, PhD, of the Regenstrief Institute and Indiana University Richard M. Fairbanks School of Public Health, Indianapolis, in a press release about the study.
“Given the incomplete protection against hospitalization afforded by monovalent COVID-19 vaccines, persons with immunocompromising conditions might benefit from updated bivalent vaccine booster doses that target recently circulating Omicron sublineages, in line with ACIP [Advisory Committee on Immunization Practices] recommendations,” the researchers concluded in the study.
The study was funded by the CDC. The researchers had no financial conflicts to disclose. The VISION Network is a collaboration between the CDC, the Regenstrief Institute, and seven health care systems across the United States: Columbia University Irving Medical Center (New York), HealthPartners (Wisconsin), Intermountain Healthcare (Utah), Kaiser Permanente Northern California, Kaiser Permanente Northwest (Washington State), the University of Colorado, and Paso Del Norte Health Information Exchange (Texas).