Dynamic changes in paediatric invasive pneumococcal disease after sequential switches of conjugate vaccine in Belgium: a national retrospective observational study, Desmet, Stefanie, Lagrou Katrien, Wyndham-Thomas Chloé, Braeye Toon, Verhaegen Jan, Maes Piet, Fieuws Steffen, Peetermans Willy E., and Blumental Sophie , The Lancet Infectious Diseases, Jan-01-2021, Volume 21, Issue 1, (2021)