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. 2017 Jan 11;12(1):e0170027. doi: 10.1371/journal.pone.0170027

Fig 1. Schematic representation of the time periods in which the strains used in this study were grouped, based on their year of isolation.

Fig 1

The periods included strains isolated before or around the time the WCVs were introduced (Introd-Vac-strains, 1949–1960) and after the introduction of the WCVs (WCV-strains, 1970–2000) or ACVs (ACV-strains, 2005–2014). The three groups are indicated in green, blue and pink respectively. The WCV was introduced in the Dutch National Immunisation programme (NIP) in 1957. In 2001, the ACVs were included in the NIP as a four year old (4yo) booster. The WCVs were fully replaced by the ACVs in 2005 (black arrows).