Stanley A Plotkin1,2, Paul Offit3,4, Pierre Bégué5. 1. University of Pennsylvania, Philadelphia, PA 19104, USA. stanley.plotkin@vaxconsult.com. 2. Vaxconsult, Doylestown, PA 18902, USA. 3. Children's Hospital of Philadelphia, Philadelphia, PA 19104, USA. 4. Perelman School of Medicine at the University of Pennsylvania, Philadelphia, PA 19104, USA. 5. Académie Nationale de Médecine, Paris 75006, France.