Estimated coefficients (), standard errors (SE) and p-values (p) of three fitted negative binomial models for influenza-associated deaths: (1) pneumonia and influenza (P&I), (2) respiratory and circulatory, and (3) all-cause in Taiwan, from October 1999 to September 2007, respectively.

*Statistically significant (p<0.05). NA, Excluded by the Akaike Information Criterion (AIC) and likelihood ratio test. α is an offset term equal to the log of elderly mid-year population size for each year. β4∼β6, coded as “1” if the vaccine of that subtype/type had been matched and “0” for others. β7 (Post-SARS Effect), coded as “1” for the months after October, 2003 and “0” for others. β8, coded 1 through 96 from October, 1999 to September, 2007. If no wild-type strain in a subtype was isolated for a certain year, the status of the flu vaccine was thus coded as “matching” for that subtype and year.