Table 2. Incidence rates and incidence rate ratios of influenza infection of healthcare workers and non-healthcare workers from subgroup meta-analyses, according to vaccination status and diagnostic methods.

Vaccination status	Diagnostic methods	Subpopulation	Number of seasons	Number of subjects	Incidence rate [95% confidence interval](n/100 population/season)	Incidence Rate Ratio[95% confidence interval]
Unvaccinated	All infections	HCWs	10	2,273	18.69 [15.80, 22.11]	3.43 [1.20, 5.67]
		Working adults	4	4,373	5.44 [3.01, 9.84]
Vaccinated	All infections	HCWs	8	3,026	6.49 [4.63, 9.09]	5.41 [2.79, 8.03]
		Working adults	2	3,717	1.20 [0.86, 1.68]
Unvaccinated	Symptomatic infections (serology)	HCWs	7	1,857	7.54 [4.86, 11.70]	1.47 [0.44, 2.50]
		Working adults	4	1,234	5.12 [3.08, 8.52]
Vaccinated	Symptomatic infections (serology)	HCWs	7	3,092	4.81 [3.23, 7.16]	1.58 [0.49, 2.67]
		Working adults	3	2,619	3.04 [1.79, 5.15]

Abbreviations: HCWs, healthcare workers.