LAUSR

To collect all available evidence on the effect of diabetes mellitus (DM) as a risk factor for pneumococcal disease incidence and related complications, and on the efficacy/effectiveness of vaccines in patients with DM. Two distinct systematic searches on MEDLINE, Cochrane, ClinicalTrials.gov and EMBASE databases were performed, one for each meta-analysis, collecting all observational (cohort and case–control) studies and randomized clinical trials performed on humans up to June 1st, 2023. We retrieved 36 observational studies comparing risk for pneumococcal disease and related complications in people with or without DM, and 11 studies (1 randomized clinical trial and 10 observational studies) assessing conjugated and polysaccaridic vaccines efficacy/effectiveness on preventing such outcomes. People with DM were at higher risk for Invasive Pneumococcal Disease (unadjusted OR 2.42 [2.00; 2.92]); Case-Fatality Rate (unadjusted OR 1.61 [1.25; 2.07], Pneumococcal pneumonia (unadjusted OR 2.98 [2.76; 3.22), and Intensive care unit admission for pneumococcal disease (unadjusted OR 2.09 [1.20; 3.66]). In diabetic individuals vaccinated with conjugated vaccine, incidence of pneumonia specific for vaccine type in a clinical trial (OR 0.237 [0.008; 0.704]), and hospitalization for overall pneumonia during the year following the polysaccharide vaccination in observational studies (unadjusted OR 0.63 [0.45–0.89]) were significantly lower in comparison with unvaccinated DM subjects, with no significant differences for other outcomes. People with diabetes mellitus are at higher risk for less favourable course of pneumococcal disease and should be therefore targeted in vaccination campaigns; more evidence needs to be collected on vaccination outcomes in people with diabetes.