[1] Dalhousie Univ, Canadian Ctr Vaccinol, IWK Hlth Ctr, Dept Paediat, 5850-5980 Univ Ave, Halifax, NS B3K 6R8, Canada
[2] WHO, Reg Off Europe, Div Communicable Dis Hlth Secur & Environm, Copenhagen O, Denmark
[3] Inst Natl Sante Publ Quebec, Quebec City, PQ, Canada