W.LIM1, W.X.LIAN1, H.L.HTUN1, G.GANESAN2, K.B.TAN2, A.L.P.CHOW1
Tan Tock Seng Hospital1, Ministry of Health Singapore2
The National Healthcare Group implemented a community-based influenza vaccination programme for about 3000 seniors annually from 2016-2018. We report the effectiveness of influenza vaccination in reducing mortality and hospitalization in the subsequent year.
Vaccinated individuals were linked to the Ministry of Health’s administrative database. Comparison groups were created by selecting patients 65 years and older living in the same postal codes. Primary outcomes were mortality in the one-year period after vaccination, and change in the rate of hospitalization in the one-year period after vaccination, compared to before. Logistic regression was performed to assess mortality, while a two-part model, with logistic regression for non-zero outcome in the first part, and log-gamma regression in the second part was used to assess hospitalization. An interaction term for vaccine status and time period was added for difference-in-difference analyses.
Vaccination was associated with a statistically significant 45-46% reduction in mortality in all 3 years (all p<0.001) and a statistically significant 60-63% reduction in mortality due to pneumonia (p=0.009-0.018). In difference-in-difference analyses, the slope of change for all-cause hospitalization from pre- to post-vaccination period was significantly higher in vaccinated than comparison group, suggesting an increase in hospitalizations in vaccinated seniors compared to non-vaccinated seniors. However, the slope of change for pneumonia-related hospitalizations was not significant, suggesting the change in hospitalizations post-vaccination compared to pre-vaccination period was similar in both groups.
Our results suggest that influenza vaccination reduced one-year all-cause and pneumonia mortality risks, and provide limited evidence that vaccination may reduce pneumonia-related hospitalizations among vaccinated seniors.