Multiple dose vaccination against childhood diseases: high coverage with the first dose remains crucial for eradication. Paulo 1 , A.C., Gomes 1 , M. C., Casinhas 2 , A.C., Horta 2 , A., Domingos 3 , T. 1 Faculdade Ciências Lisboa, and Center of Mathematics and Fundamental Applications DBV, Bloco C2, Piso 4 Campo Grande 1749-016 Lisboa, Portugal Ph. 3511-7573141 ext. 1558 FAX: 3511-7500048 e-mail: mcgüfc.ul.pt 2 Instituto Superior Técnico Av Rovisco Pais, 1 1049-001 Lisboa, Portugal 3 Non-Linear Dynamics Group Instituto Superior Técnico Av Rovisco Pais, 1 1049-001 Lisboa, Portugal Please address all correspondence to M.C. Gomes 1