Table 1.

Observational studies of pneumococcal polysaccharide vaccine effectiveness (VE) against invasive pneumococcal disease (IPD) in older adults.

Reference, study design	Study population	Subgroup	No. of cases of IPD	VEa (95% CI)
Shapiro and Clemens [2]
Case control	Adults with an indication for pneumococcal vaccination admitted to Yale-New Haven hospital in Connecticut	All	90	67 (13–87)
		Immunocompromised	20	0 (−1228 to 93
Forrester et al. [3]
Case control	Persons ≥55 years of age admitted to the Denver Veterans Administration hospital	All	89	−34 (−176 to 35)
Indirect cohortb	Persons ≥55 years of age admitted to the Denver Veterans Administration hospital	All	89	−21 (−221 to 55)
Sims et al. [4]
Case control	Immunocompetent persons ≥55 years of age admitted to 1 of 5 hospitals in Pennsylvania	All	122	70 (36–86)
Shapiro et al. [5]
Case control	Adults with an indication for pneumococcal vaccination admitted to 1 of 11 hospitals in Connecticut	All	983	56 (42–67)
		Immunocompetent	808	61 (47–72)
		Immunocompromised	175	21 (−55 to 60)
Indirect cohortb	Adults with an indication for pneumococcal vaccination admitted to 1 of 11 hospitals in Connecticut	All	932	48 (3–72)
Butler et al. [6]
Indirect cohortb	Persons ≥5 years of age in the United States	All	2837	57 (45–66)
		Immunocompetent, ≥65 years of age	525	75 (57–85)
		Anatomic asplenia, excluding persons with sickle cell disease	166	77 (14–95)
Farr et al. [7]
Case control	Persons ≥2 years of age with an indication for pneumococcal vaccination admitted to the University of Virginia Health Sciences Center in Virginia	All	85	81 (34–94)
Benin et al. [8]
Case control	Navajo adults ≥18 years of age with an indication for vaccination	All	108	26 (−29 to 58)
Indirect cohortb	Navajo adults ≥18 years of age	All	278	35 (−33 to 69)
Jackson et al. [9]
Cohort	Community-dwelling members of a Washington State health plan ≥65 years of age	All	61	44 (7–67)
		Immunocompetent	39	54 (13–76)
		Immunocompromised	22	22 (−87 to 68)
Hedlund et al. [10]
Cohort	Residents of Stockholm County, Sweden, ≥65 years of age who were invited to receive influenza and pneumococcal vaccination in the fall of 1998	All	40	48 (3–72)
Andrews et al. [11]
Indirect cohortb	Persons ≥65 years of age in Victoria, Australia	All	98	79 (−14 to 96)
Dominguez et al. [12]
Case control	Persons ≥65 years of age admitted to 12 hospitals in Catalonia, Spain	All	149	70 (48–82)
		Immunocompetent	103	76 (51–88)
		Immunocompromised	31	50 (−44 to 82)
Vila-Córcoles et al. [13]
Cohort	Community-dwelling adults ≥65 years of age in Catalonia, Spain	All	22	40 (−165 to 78)
Singleton et al. [14]
Indirect cohortb	Native Alaskan adults ≥20 years of age	All	300	75 (27–91)
Mooney et al. [15]
Screening method	Persons ≥65 years of age in Scotland	Immunocompetent	135	62 (45–73)
		Immunocompromised	35	37 (−80 to 70)

^aVE is a percentage calculated as 1 – relative risk of disease in vaccinated versus nonvaccinated individuals. A negative VE estimate indicates a higher risk among vaccinated individuals, compared with nonvaccinated persons; a 0% VE estimate indicates no difference in risk between vaccinated and nonvaccinated individuals; and a positive VE indicates a lower risk among vaccinated individuals, compared with nonvaccinated persons. If the 95% CI for the VE estimate extends from negative to positive or includes zero, the VE estimate is not considered to be statistically significant.

^bThe indirect cohort design includes only cases of IPD; VE is estimated by comparing the distribution of pneumococcal serotypes in vaccinated and nonvaccinated persons with IPD. This serotype distribution method is based on the assumption that, if the vaccine is effective, vaccine serotypes will be less common among vaccinated persons, than among nonvaccinated persons.