Abstract The purpose of this study was to determine vaccination rates against influenza and pneumococcus in a large cohort of adults hospitalized with confirmed influenza A(H1N1) pdm09 infection, and to identify differences in clinical features, frequency of bacterial coinfection, and outcomes between vaccinated and non-vaccinated patients. A prospective cohort study conducted at 14 teaching hospitals in Spain. Adult patients (n=699) hospitalized with confirmed influenza A(H1N1)pdm09 infection during the pandemic and the first post pandemic influenza periods were included. Vaccination status against influenza and pneumococcus was established in 547 and 587 individuals, respectively. The vaccination rates were low: 14% for seasonal influenza and 5.4% for pneumococcus. Despite conducting whole population and subgroup multivariate analyses, we observed no beneficial effects on outcomes (intensive care unit admission and mortality) for both vaccines. However, patients who had been vaccinated, whether against influenza or pneumococcus, did tend to develop fewer bacterial coinfections, particularly that due to S. pneumoniae.
Keywords: influenza A (H1N1); seasonal influenza; vaccination; pneumococcal vaccine; outcome; mortality