Emergence of Streptococcus pneumoniae serotype 15A after the introduction of the conjugate vaccine in Victoria

To the Editor: Streptococcus pneumoniae (the pneumococcus) is a major cause of severe bacterial disease worldwide. Since the introduction of the pneumococcal conjugate vaccine (PCV) there have been changes in the epidemiology of invasive pneumococcal disease (IPD), with an increase in infections with pneumococcal serotypes not included in the conjugate vaccines.1 The Microbiological Diagnostic Unit Public Health Laboratory at the University of Melbourne commenced pneumococcal serotyping in 1994. Before the PCV was included in the national immunisation schedule in 2005, a single isolate of S. pneumoniae serotype 15A, a non-vaccine serotype, had been detected in 1999 among Victorian invasive infections. The next serotype 15A invasive isolate was not seen until April 2009. The number of serotype 15A infections began increasing thereafter and accounted for 4% (13/295) of Victorian IPD from 1 January until 30 September 2012.