Effectiveness of the 13-valent pneumococcal conjugate vaccine against adult pneumonia in Italy: a case-control study in a 2-year prospective cohort

Objectives Current strategies to prevent adult pneumococcal disease have been recently reviewed in Italy. We did a postlicensure study to estimate the direct vaccine effectiveness (VE) of the 13-valent pneumococcal conjugate vaccine (PCV13) against adult pneumococcal community-acquired pneumonia (pCAP). Study design Between 2013 and 2015, a 2-year prospective cohort study of adults with CAP was conducted in the Apulia region of Italy where the average vaccine uptake of PCV13 was 32% among adults >= 65 years. The test-negative design was used to estimate VE against all episodes of confirmed pCAP and vaccine-type (VT)-CAP. VE in a subgroup of patients managed in the community was also estimated using a matched case control design. VE was calculated as one minus the OR times 100%. Results The overall VE of PCV13 was 33.2% (95% Cl 106.6% to 82%) against pCAP irrespective of serotype and 381% (950!o CI - 131.9% to 89%) against VT-CAP in the cohort of adults >= 65 years. The VE was 42.3% (95% CI 244.1% to 94.7%) against VT-CAP in the age group at higher vaccine uptake. For the subgroup of cases managed in the community, the overall VE against disease due to any pneumococcal strain was 88.1 % (95% CI 4.2 / to 98.5%) and 91.7% (95% CI 13.1 % to 99.2%) when we controlled for underlying conditions. Conclusions Although our results are non-significant, PCV13 promises to be effective against all confirmed pCAP already with modest levels of uptake in the population of adults >= 65 years of age. Larger studies are needed to confirm the direct vaccine benefits.