Dual influenza and pneumococcal vaccination was associated with lower short-term risks of all-cause and acute respiratory hospitalizations among the elderly in Shenzhen, China: a retrospective cohort

Objectives The present study aimed to evaluate the real-world effectiveness of receiving both influenza and pneumococcal vaccines among Chinese elderly, the evidence on which has been sparse by far. Methods Outpatient and inpatient claims databases from Jan 1, 2015 - Apr 1, 2017 of persons at least 60 years old in Shenzhen were merged with local registry of influenza vaccines and 23-valent pneumococcal polysaccharide vaccines (PPSV23) from Oct 1, 2016 - May 31, 2017. Individuals who were vaccinated with influenza between Nov 1 - Dec 31, 2016 and received a PPSV23 shot 30 days within the date of influenza vaccination were defined as the vaccinated group. A control group consisted of individuals that received neither of the vaccines was constructed by matching on year of birth, sex, and district. The two outcomes were all-cause and acute respiratory hospitalizations. Difference-in-difference (DiD) logistic regressions that were proceeded with an entropy balancing (EB) process were used to analyze the effectiveness of dual-vaccination. Results A total of 48,116 eligible individuals were identified in the vaccinated group, which were matched by 93,692 individuals in the control group. The two groups had statistically significant difference in 27 out of 28 demographic and baseline characteristics before EB, all of which were balanced after EB. The DiD analyses estimated that dual-vaccination was associated with lower short-term risks of all-cause (odds ratio: 0.59, CI: 0.55-0.63) and acute respiratory (odds ratio: 0.49, CI: 0.41-0.59) hospitalizations. Conclusions Influenza and PPSV23 dual-vaccination may reduce all-cause and acute respiratory hospitalizations among Chinese elderly.