Other studies reach similar conclusions
The study findings fall into line with other studies of patient populations on immunosuppressants. A retrospective cohort study of Veterans Affairs patients with inflammatory bowel disease who were taking immunosuppressants, published in Gastroenterology, found that full vaccination with either Moderna and Pfizer-BioNTech vaccines was about 80% effective. Another retrospective cohort study of data from the National COVID Cohort Collaborative, published in JAMA Internal Medicine, reported that full vaccination significantly reduced the risk of COVID-19 breakthrough infection regardless of immune status. Immunosuppressed patients in this study had higher rates of breakthrough infections than immunocompetent patients, but the disparities were in line with what Dr. Zhao and the University of Michigan researchers reported.
A review of 23 studies of COVID-19 vaccinations, published in Lancet Global Health, found that immunocompromised people – 1,722 of whom were included in the studies – had lower rates of producing antibodies after two vaccine doses than did immunocompetent people, ranging from 27% to 92%, depending on the nature of their immunocompromised status, compared with 99% for the immunocompetent.
Strengths and limitations
One strength of the Michigan study is the quality of data, which were drawn from the Michigan Medicine electronic health record, Dr. Zhao said. “So, we know who received the vaccine and who didn’t. We also have access to data on patient health conditions, such as comorbidities, in addition to demographic variables (age, gender, and race), which were controlled in making fair comparisons between immunosuppressants and immunocompetent groups.”
Dr. Alfred Kim
Alfred Kim, MD, PhD, an assistant professor of internal medicine and rheumatology at Washington University in St. Louis, who was not involved with the study, credited Dr. Zhao and associates for delivering the first data that specifically quantified COVID-19 risk reduction in a large study population. Although he noted that the large sample size and the design reduced the chances of confounding and were strengths, he said in an interview that “lumping” the patients taking immunosuppressive drugs into one group was a weakness of the study.
“Clearly, there are certain medications (B-cell depleters, mycophenolate, for example) that carry the greatest risk of poor antibody responses post vaccination,” he said. “One would have to guess that the greatest risk of breakthrough infections continues to be in those patients taking these high-risk medications.”
Another possible problem, which the authors acknowledged, is spotty SARS-CoV-2 testing of study participants – “a systemic issue,” Dr. Kim noted.
“The easiest and most durable way to reduce the risk of getting COVID-19 is through vaccination, period,” he said. “Now we have infection-rates data from a real-world study cohort to prove this. Furthermore, boosting clearly provides additional benefit to this population.”
The National Institute of Allergy and Infectious Diseases provided funding for the study. Dr. Zhao, Dr. Zhao’s coauthors, and Kim disclosed no relevant financial relationships.
A version of this article first appeared on Medscape.com.