[1] Univ British Columbia, Dept Obstet & Gynaecol, Vancouver, BC, Canada
[2] McGill Univ, Dept Epidemiol Biostat & Occupat Hlth, Montreal, PQ, Canada
[3] Grp Hlth Res Inst, Seattle, WA USA
[4] McGill Univ, Dept Pediat, Montreal, PQ, Canada
[5] WHO, Initiat Vaccine Res, Geneva, Switzerland
[6] Brown Univ, Dept Epidemiol, Providence, RI 02912 USA
[7] Brown Univ, Dept Obstet & Gynecol, Providence, RI 02912 USA