Increase in incidence of invasive pneumococcal disease caused by serotype 3 in children eight years after the introduction of the pneumococcal conjugate vaccine in Hong Kong

This study used several datasets of reported and serotyped invasive pneumococcal disease (IPD) cases to estimate vaccine and non-vaccine type incidence in Hong Kong children. Incidence was analyzed by four time periods to indicate pre-PCV (period 1, 1995-2004), private market only (period 2, 2006-2009), and following early (period 3, 2010-2014, mixed use of 7-, 10- and 13-valent vaccines) and more than five years (period 4, 2015-2017, 13-valent vaccine only) of routine implementation (since September 2009). IPD incidence decreased by 85% and 35% in aged < 2 years and aged 2 to < 5 years, respectively, from period 1 to period 4. This was due to a 97% reduction in the serotypes covered by 7-valent vaccine. In period 4, 59% of the disease was caused by serotype 3 and was largely attributed to an ermB positive, novel ST6011 clone. The finding corroborates an increasing body of evidence that the efficacy of the 13-valent vaccine against infection by this serotype is low.