COVID-19 vaccines worked fairly well in keeping immunocompromised patients out of the hospital from the infection, but still less than for those with a competent immune system, a study showed.

After two vaccine doses, immunocompromised patients saw 77% vaccine effectiveness (95% CI 74%-80%) against hospitalization for confirmed COVID-19, with a 3.9% rate of SARS-CoV-2 test positivity in hospital compared with 11.8% among those who were unvaccinated.

Effectiveness was similar between Moderna and Pfizer for these patients but did vary by type of immunocompromise, ranging from 59% for solid organ or stem cell transplant recipients to 81% in those with a rheumatologic or inflammatory condition.

For immunocompetent patients in hospital, vaccine effectiveness came in at the expected 90% (95% CI 89%-91%), with 3.8% versus 24.8% positive tests with and without vaccination, respectively, reported Peter J. Embi, MD, of the Regenstrief Institute, a research organization affiliated with the Indiana University School of Medicine in Indianapolis, and colleagues in the Morbidity and Mortality Weekly Report.

Their study of some 89,000 hospitalizations for COVID-like illness accounted for age, local virus circulation in patients’ community, and other factors.

“Immunocompromised persons benefit from and should receive COVID-19 vaccines,” the researchers concluded, saying that their findings of lower effectiveness compared with the immune-competent supported recent CDC recommendations for this high-risk population.

The CDC’s Advisory Committee on Immunization Practices (ACIP) in August recommended that moderately to severely immunocompromised people vaccinated with an mRNA vaccine should get three doses. Interim CDC guidance in October also recommended a booster for vaccine recipients who are immunocompromised 6 months or more after their third mRNA dose, or at least 2 months after the single-dose Johnson & Johnson regimen (for two total doses).

“In addition to vaccination, immunocompromised persons should implement nonpharmaceutical prevention strategies such as masking to help prevent SARS-CoV-2 infection, and, if infected with SARS-CoV-2, be monitored closely and considered early for proven therapies that might prevent progression to severe illness (e.g., monoclonal antibodies),” Embi’s group added.

Their study utilized data from the VISION Network — a group of 187 hospitals in nine U.S. states collaborating with the CDC — to look at 69,116 immunocompetent and 20,101 immunocompromised adult patients admitted for COVID-19-like illness. Patients had available molecular testing results for SARS-CoV-2 from Jan. 17 through Sept. 5, 2021.

Overall, 43% of the immunocompromised patients and 53% of the rest had gotten two doses of an mRNA COVID-19 vaccine at least 14 days (median 89 days) before their hospitalization and were considered fully vaccinated.

Vaccine effectiveness was also similar between age groups and timing of hospitalization relative to the prevalence of the Delta variant in the state of hospitalization.

Study limitations included potential variation in prevalence of respiratory virus infections, other than COVID-19, among immunocompromised versus immunocompetent patients. However, Embi’s group wrote that their test-negative design meant that such a difference would not be expected to influence the validity of vaccine effectiveness estimates stratified by immunocompromised status.

Also, discharge diagnoses, such as cancer and rheumatoid arthritis, were used as a surrogate for immunocompromise, which could have led to some misclassification; selection bias couldn’t be ruled out if vaccination status influenced the likelihood of SARS-CoV-2 testing; and the study excluded the Johnson & Johnson vaccine.