Tor Härnqvist, a doctoral student at the University of Gothenburg, infectious disease physician at NU Hospital Group, and co-lead author, noted that because these tests are not standard after severe pneumococcal infection, “we may miss patients with undiagnosed blood cancer or immunodeficiency,” along with the opportunity to begin treatment.2
Antibody Deficiencies Persist After Recovery
Nearly half of patients (44%) sampled during acute infection and 34% sampled during convalescence had at least 1 Ig isotype or IgG subclass below the lower limit of the reference interval, compared with 16% of controls. During convalescence, levels of IgA, IgG2, or IgG4 were low in 16% to 20% of patients vs 0% to 2% of controls. IgG2 is of particular concern, as it makes up a major share of the antibodies that target encapsulated bacteria such as pneumococci.1
Follow-up evaluation identified primary Ig deficiency in 3 patients, and 7 patients started Ig replacement therapy, including several with secondary immunodeficiency related to a known hematologic malignancy or prior rituximab treatment. Circulating B-cell counts also remained below the reference interval in 40% of patients 2 to 4 months after infection, compared with 13% of controls. Because Ig levels can drop during acute infection, the authors noted that low values in this phase should be confirmed after recovery.1
The investigators acknowledged several limitations. Only 37% of eligible patients enrolled, about half provided convalescent samples, and controls were not hospitalized and had fewer comorbidities. Serum free light chains were also not assessed, which may have led to underdetection of light-chain MGUS.1
Implications for Vaccination and Pharmacy Practice
The findings carry implications for pneumococcal immunization. Pneumococcal vaccination is recommended for patients with MGUS, but high M protein concentrations are associated with weaker vaccine responses, underscoring the value of earlier MGUS diagnosis.1
The CDC currently recommends a pneumococcal conjugate vaccine (PCV15, PCV20, or PCV21) for all adults aged 50 years or older who have never received a conjugate vaccine or whose history is unknown. If PCV15 is used, a dose of PPSV23 should follow 1 year later, with a minimum 8-week interval considered for adults with immunocompromising conditions.3
Co-lead author Karin Bergman, a doctoral student and infectious disease physician at Södra Älvsborg Hospital, noted that serotypes covered by the Swedish childhood vaccine have declined sharply but have been largely replaced by nonvaccine serotypes. These frequently affect older adults and those with cancer or compromised immune systems. Bergman said adult vaccine recommendations should account for which vaccines are used in children and which serotypes circulate as a result.2
For pharmacists, the study reinforces the importance of reviewing pneumococcal vaccination status in older adults and in patients with known or suspected immunocompromising conditions. The study authors concluded that M protein and Ig assessment could be considered after an IPD episode, though larger studies are needed to confirm which patients benefit most.1
“Pharmacists can contribute by reviewing whether appropriate follow-up has been arranged and encouraging patients to discuss further evaluation with their treating physician when indicated. Further studies are needed to determine which patients would benefit most from immune assessment,” Härnqvist said in an interview with Pharmacy Times.
REFERENCES1. Härnqvist T, Bergman K, Mellgren Å, et al. Invasive pneumococcal disease unmasks monoclonal immunoglobulins and antibody deficiencies: a multicenter prospective study in adults. Sci Rep. 2026;16:23203. doi:10.1038/s41598-026-61992-82. Pneumonia can reveal undiagnosed blood cancer. News release. EurekAlert! September 30, 2026. Accessed October 1, 2026. https://www.eurekalert.org/news-releases/11460143. Pneumococcal vaccine recommendations. CDC. Updated February 25, 2026. Accessed October 1, 2026. https://www.cdc.gov/pneumococcal/hcp/vaccine-recommendations/index.html