A single dose of monovalent non-adjuvanted influenza A (H1N1) pdm09 vaccine was 50% effective at preventing hospitalization related to the infection, researchers from the CDC have found.
According to the report in Clinical Infectious Diseases, recent data have suggested that such vaccines were 69% effective at preventing influenza during the 2009 pandemic. Studies on vaccine effectiveness against hospitalization have ranged from 49% to 90%.
The researchers used CDC’s Influenza Surveillance Network to identify patients with laboratory-confirmed H1N1 infections who were matched with two community controls. The patients and the controls underwent structured telephone interviews, which the researchers used, along with medical and hospital records, to determine patient characteristics, vaccination status and the presence of medical conditions associated with increased risk for influenza complications.
The study included 217 patients who were hospitalized with influenza from Dec. 5, 2009, to April 30, 2010. Among these patients, 14% were immunized compared with 22% of the 413 community controls. After adjustment for age, race, ethnicity, region, high-risk respiratory condition, month of index case illness onset, education, insurance status and presence of high-risk, non-pulmonary medical condition, the vaccine effectiveness was 50% (95% CI, 13-71).
“Our results suggest that a single dose of monovalent non-adjuvanted A(H1N1)pdm09 vaccine prevented one-half of the potential hospitalizations associated with A(H1N1)pdm09 virus infection,” the researchers wrote. “This finding confirms previous reports of the preventive benefit of the vaccine, and adds to the evidence indicating that influenza vaccines have the potential to prevent a substantial proportion of influenza-associated hospitalizations.”