Vaccinations in the immunocompromised population: Paramount and paradox

Immunocompromised patients are at increased risk of infection, but vaccinations are often less effective. In this thesis we investigated the risk of pneumonia, pneumococcal infections and measles (part 1) and the response to two important vaccines, against pneumococcal disease and hepatitis A (part 2) in immunocompromised adults.
The risk of invasive pneumococcal disease is 7-fold increased among people living with HIV and 5-32-fold increased among adults with cancer compared with the general Dutch population. Pneumococcal vaccination of immunocompromised patients is recommended and guidelines advise to use the 13-valent pneumococcal conjugate vaccine (PCV13) followed by the 23-valent polysaccharide vaccine (PPSv23). A meta-analysis of 19 studies among HIV patients showed that this combined schedule is superior to single PCV13 or PPSV23, however vaccination responses are impaired compared with controls. We observed a protection rate of 49-59% in patients with HIV and use of immunosuppressive medication for inflammatory bowel disease, compared with 81-82% in controls. After stem cell transplantation only 24-47% of patients were protected, due to a poor response to PPSV23. Following hepatitis A vaccination seroprotection is much higher (53-90% after 2 vaccine doses), however many individuals are unprotected after the first dose. Therefore, hepatitis A antibody assessment prior to travel to hepatitis A endemic areas is recommended. Duration of protection remains unclear. Concluding, vaccinations are less effective for the population that need them the most. Further research into novel vaccination strategies for these patients is needed.