Particular Characteristics of Encapsulated Bacteria

Abstract

The referenced article (1) also applies to hematological and oncological patients. The administration of dead vaccines is safe three to six months after the end of chemotherapy, although vaccine effectiveness may be reduced. Administration of attenuated live vaccines, however, has to be pondered very carefully. The Infectious Diseases Working Party of the German Society of Hematology and Oncology has published appropriate methods (www.dgho-infektionen.de). A warning to accompany the unequivocal indication for prophylactic vaccination against encapsulated bacteria: such vaccines do not guarantee protection from infection. Meta-analyses have shown that polysaccharide vaccines in chronically ill patients do not reduce the lethality of invasive pneumococcal disease (2). Evaluating surrogate markers rather than clinical end points in studies partially explain this association. The licensed pneumococcal polysaccharide vaccine has thus far not been adequately studied in hematology/oncology patients. Differences between vaccines also deserve attention: Pneumococcal polysaccharide vaccines—in contrast to conjugated vaccines—provoke T-cell independent, IgM dominant immune responses and lead to immunological short term memory. Because of the improved response to vaccination with conjugated vaccines in vaccine-naive immune systems, children receive conjugated vaccines. Successful studies of sequential polysaccharide vaccines and conjugated vaccines have been conducted in people who received stem cell transplants (3), accordingly, vaccination in this clientele is now being promoted. Expanding the license approval of the 13-valent conjugate vaccine from children younger than 5 years to adults older than 50 years is being investigated (www.pfizer.com). The vaccination might counterbalance the increasing antibiotic resistance of pneumococci. In reverse, increase in serotypes that are not captured by licensed vaccines might become a clinical problem. Other vaccine-preventable encapsulated bacteria may have vaccination gaps. The incidence of Haemophilus influenzae type B seems to be lower in adults than the incidence of non-encapsulated Haemophilus strains, which moreover are associated with higher letality (4). 50% of meningococci in Germany are of serotype B, and no vaccine exists for that serotype. For this reason, anti-infective prophylaxis should be considered after exposure, even in individuals who have been vaccinated. It seems obvious that clinical research into vaccination in at-risk adult patients needs to be intensified.