Pfizer and Moderna's COVID-19 vaccines may be less effective at preventing hospitalization among fully vaccinated immunocompromised people, a Nov. 2 CDC study found.
CDC researchers analyzed clinical data from 187 hospitals in nine states between Jan. 17 and Sept. 5.
Two doses of an mRNA vaccine were 77 percent effective at preventing COVID-19 hospitalizations among immunocompromised adults, compared to 90 percent for immunocompetent adults. This difference was consistent across vaccine types, patient age groups and the timing of hospitalizations relative to the delta variant's dominance in each state.
"Immunocompromised persons benefit from COVID-19 mRNA vaccination but are less protected from severe COVID-19 outcomes than are immunocompetent persons," the CDC said.
The finding builds on past research suggesting immunocompromised people may not develop high levels of antibodies after vaccination. Per CDC recommendations, these individuals should receive three doses of an mRNA vaccine, along with a booster.
The CDC estimates about 3 percent of adults in the U.S. are immunocompromised.