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Age influences efficacy of Prevnar 13
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The efficacy of the Prevnar 13 vaccine decreased with advancing age in immunocompetent patients, according to the results of a post-hoc analysis.
Cornelius H. van Werkhoven, MD, of the University Medical Center Utrecht, the Netherlands, and colleagues analyzed data from the Community-Acquired Pneumonia Immunization Trial in Adults (CAPiTA), a randomized, double blind, placebo-controlled study that included 84,496 immunocompetent elderly patients.
Patients were assigned either Prevnar 13 (13-valent pneumococcal conjugate vaccine, Pfizer; PCV13) or placebo. Overall, 84,492 patients met the primary endpoint of the trial: community-acquired pneumonia (CAP) caused by any of the 13 vaccine serotypes, the researchers wrote in Clinical Infectious Diseases.
All patients provided a urine sample for serotype-specific urinary antigen detection, blood cultures were collected, and Streptococcus pneumoniae strains were serotyped.
Median patient age for the vaccine and placebo groups was 71.6 years. During follow-up (mean, 3.9 years), 7.1% of patients died, and 5.4% were lost to follow-up.
In the modified intention-to-treat population, which included CAP and invasive pneumococcal disease (IPD) episodes occurring more than 14 days after vaccination, there were 184 first episodes of vaccine-type CAP (VT-CAP) and vaccine-type IPD (VT-IPD).
The results showed that model-predicted PCV13 efficacy in preventing VT-CAP and VT-IPD was 65% in patients aged 65 years (95% CI, 38%-81%) and dipped to 40% in patients aged 75 years (95% CI, 17%-56%).
“In this study of immunocompetent subjects, aged 65 years and older, efficacy of PCV13 in preventing VT-CAP or VT-IPD was highest among those subjects aged 65 at the time of randomization, and [virus efficacy] declined with increasing age,” van Werkhoven and colleagues wrote. “A similar finding was obtained in the per protocol analysis, which was limited to subjects that were immunocompetent at the time of their first CAP or IPD episode.”
Possible study biases were other baseline characteristics, such as comorbidities associated with age and with different vaccine efficacy. The researchers said after such adjustments, however, the efficacy estimate remained unchanged.
Age-related decreases in antibody avidity may have caused the differences in efficacy, as similar results have been seen with Pneumovax 23 (23-valent pneumococcal polysaccharide vaccine, Merck) and Prevnar 7 (7-valent pneumococcal conjugate vaccine, Pfizer). Age-related changes in the immune system may also be to blame, according to the investigators. – by Colleen Owens
Disclosure: van Werkhoven reports having served on a Pfizer advisory board. Please see the full study for a list of all other authors’ relevant financial disclosures.
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