Table 2 Characteristics of included studies (continued)

 Tobudic, 2012¹ [31]

1 (longitudinal cohort)

7 day diary (after revaccination dose)

Population characteristics: Participants 1 year older at 2^nd dose

Safety: no comparison group

 Dransfield, 2012¹ [23]

2 (1^st vs. 2^nd dose)

not assessed

Population characteristics: 2^nd dose recipients older, more often white, more severe COPD disease

Safety: −

 Hammitt, 2011 [11]

3 (1^st vs. 2^nd or 3^rd dose)

4 day diary and interview on day 30

Population characteristics: 2^nd/3^rd dose recipients older, more likely Alaska Natives/American Indians, more often with underlying comorbidities compared to 1^st dose recipients

Safety: local AEs and systemic AEs more frequent in revaccination group

 Jackson, 1999 [13]

2 (1^st vs. 2^nd dose)

13 day diary and telephone interview

Population characteristics: 2^nd dose recipients more often females and less often with underlying comorbidities

Safety: local AEs more frequent in revaccination group at days 0–2, no differences after 6 days. No differences regarding systemic AEs. Multivariate analysis: revaccination independently associated with risk of sizable local reaction

 Jackson, 2013 [22]

1 (longitudinal cohort)

13 day diary

Population characteristics: Participants 3.4–5 years older at 2^nd dose

Safety: local AEs and systemic AEs more frequent in revaccination group

 Manoff, 2010² [25]

2 (1^st vs. 2^nd dose)

not assessed

Population characteristics: 2^nd dose recipients more likely ever smoked

Safety: −

 Musher, 2010³ [12]

2 (1^st vs. 2^nd dose)

14 day diary

Population characteristics: 2^nd dose recipients more often with underlying comorbidities

Safety: local AEs and systemic AEs more frequent in revaccination group

 Musher, 2011^3,4 [28]

2 longitudinal cohorts (1^st vs. 2^nd; 2^nd vs. 3^rd)

14 day diary

Population characteristics: Participants of both longitudinal cohorts were ten years older at 2^nd/3^rd dose

Safety⁵: local AEs and systemic AEs more frequent in revaccination group

 Ohshima, 2014 [29]

1 (longitudinal cohort)

14 day diary

Population characteristics: Participants were 7.6 years older at 2^nd dose

Safety: local AEs and systemic AEs more frequent in revaccination group

 Törling, 2003 [24]

1 (longitudinal cohort)

not assessed

Population characteristics: Participants were 5.3 years older at 2^nd dose and 11% had a new episode of pneumonia

Safety: no comparison group

 Jackson, 2006 [27]

3 (1^st vs. 2^nd vs. 3^rd dose)

ICD-9-Codes

Population characteristics: 3^rd dose recipients were older and had more likely underlying comorbidities

Safety: Presumptive medically attended injection site reaction more frequent in 2^nd dose recipients than in 1^st dose recipients. No statistically significant differences between 1^st dose and 3^rd dose recipients

 Shih, 2002 [30]

2 (1^st vs. ≥ 2^nd dose)

ICD-9-Codes

Population characteristics: 2^nd dose recipients were older, more often white and had higher hospitalizations rates and a higher comorbidity (Charlson) Index

Safety: Mulitivariate analysis: Revaccination independently associated with emergency room visits and office visits if PPSV-23 was administered within 5 years. No association after >5 years.

 Walker, 2005 [32]

2 (1^st or 2^nd vs. ≥ 3^rd dose)

ICD-9-Codes and medical records

Population characteristics: ≥ 3^rd dose recipients were older and had more likely underlying lung diseases

Safety: No differences in risk of medically attended AEs in the different groups

 D’Heilly, 2002 [26]

2 (1^st vs. ≥ 2^nd dose)

Interview 8 months (on average) after vaccination

Population characteristics: not reported

Safety: Multivariate analysis: Revaccination independently associated with redness or swelling at injection site during week after vaccination