The Effectiveness of 23-valent Pneumococcal Polysaccharide Vaccine on Elderly Colorectal Cancer Long-Term Survivors: A population-based exact-matched cohort study

Abstract

Colorectal cancer (CRC) long-term survivor is a rapid enlarging group. However, the effectiveness of 23-valent pneumococcal polysaccharide vaccine (PPSV23) on this group is unknown. This nationwide population-based study in Taiwan was designed to examine the effect of PPSV23 on incidence rate ratio (IRR) of pneumonia hospitalization, cumulative incidence, and overall survival rate for these long-term CRC survivors. This cohort study was based on the Taiwan Cancer Registry and Taiwan National Health Insurance Research Database from 2000-2017. After individual exact matching to covariates with 1:1 ratio, there were a total of 1,355 vaccinated and 1,355 unvaccinated survivors. After adjusted by multivariate Poisson regression model, vaccinated group had a non-significantly lower pneumonia hospitalization risk than unvaccinated, with an adjusted IRR of 0.879 (p = .391). Besides, vaccinated group had both lower cumulative incidence rate and higher overall survival time than unvaccinated.

Keywords: Pneumococcal polysaccharide vaccine; colorectal cancer; hospitalization; pneumonia; survivor.

Figure 1.

Study design flowchart of cohort study for elderly colorectal cancer long-term survivors with and without PPSV23 vaccination. *Free PPSV23 policy in Taiwan started since year 2007 for people aged ≥75 years. ^#Month distribution of PPSV23 vaccination listed in table 1 showed most elderly colorectal cancer patients received PPSV23 within October to December, 2008 winter. The “vaccination period,” October 2008 to December 2008, is set to reduce immortal time bias and the observation time for study and control groups both started from 2009/1/1. **Cancer patients who survived at least 5 years by the time of year 2007, i.e., had cancer diagnosis before year 2002, were defined as long-term cancer survivors.

Figure 2.

Comparison of cumulative incidence rate of pneumonia hospitalization between elderly colorectal cancer long-term survivors with and without PPSV23 vaccination (p = .322). Orange line = with PPSV23 vaccination, blue line = without PPSV23 vaccination.

Figure 3.

Kaplan-Meier survival curves for elderly colorectal cancer long-term survivors with and without PPSV23 vaccination (p = .123). Orange line = with PPSV23 vaccination, blue line = without PPSV23 vaccination.