Correction: Implementing WHO guidance on conducting and analysing vaccination coverage cluster surveys: Two examples from Nigeria

• John Ndegwa Wagai, 
• Dale A. Rhoda, 
• Mary L. Prier, 
• Mary Kay Trimner, 
• Caitlin B. Clary, 
• Joseph Oteri, 
• Bassey Okposen, 
• Adeyemi Adeniran, 
• M. Carolina Danovaro-Holliday, 
• Felicity T. Cutts