Response to Pneumococcal Vaccination in Patients After Community Acquired Pneumonia With Streptococcus Pneumoniae Compared to Pneumonia Patients With Another Pathogen.

1. Introduction & rationale Community acquired pneumonia (CAP) is an important health problem with significant morbidity, mortality and cost. It is one of the main causes of disease and death worldwide and causes the most deaths by infection in the United States. Streptococcus pneumoniae is the most commonly identified pathogen in CAP.(1)

S. pneumoniae is a gram-positive, alpha haemolytic bacterium that is surrounded by an external polysaccharide capsule. There is a difference in composition of this capsule between the 92 different serotypes of S. pneumoniae. Each serotype differs in virulence and prevalence. The external polysaccharide capsule is the main trigger for the specific antibody response and is the basis for pneumococcal vaccines. As it is impossible to develop a vaccine that protects children, immune compromised adults and older adults to all serotypes, the vaccines are based on the most common and virulent serotypes.

Nowadays a 13-valent pneumococcal conjugate vaccine, Prevnar 13 (PCV13), is used widely to vaccinate children. This vaccine contains the seven serotypes present in PCV7 (4, 6B, 9V, 14, 18C, 19F and 23F) plus the emerging serotypes 1, 3, 5, 6A, 7F and 19A.(2) In the Netherlands however the 10-valent pneumococcal conjugate vaccine, Synflorix (PCV10), is still used to vaccinate children in the national infant vaccination.(3)

Van Mens et al investigated the contribution of S. pneumoniae in CAP by measuring serologic responses in patients who were hospitalized due to CAP in the Ovidius and Triple P study, two consecutive clinical trials initiated by the St Antonius Hospital Nieuwegein. This analysis showed a much higher proportion of patients with pneumococcal pneumonia than was diagnosed by conventional methods alone (i.e. blood cultures, sputum cultures or urine antigen tests). Interestingly some patients with a culture proven pneumococcal pneumonia did not show a serotype specific antibody response to the infecting serotype.(4) Possibly these patients had a temporarily low titre due to the infection but another explanation is that there might be a structurally impaired immune response against S. pneumoniae or certain serotypes.

Borrow et al vaccinated 107 children with PCV7 after invasive pneumococcal disease (IPD) following a routine infant immunization schedule. Pneumococcal serotype specific antibody measurements were performed and showed failure to respond to the infecting serotype in 8 children, even though these children received 2 or more doses of PCV. Two children failed to respond to a serotype different than the infecting serotype.(5)