[1] Johns Hopkins Bloomberg Sch Publ Hlth, Dept Int Hlth, Baltimore, MD 21205 USA
[2] Johns Hopkins Bloomberg Sch Publ Hlth, Int Vaccine Access Ctr, Baltimore, MD 21205 USA
[3] Yale Sch Publ Hlth, Dept Epidemiol Microbial Dis, New Haven, CT USA
[4] Yale Sch Publ Hlth, Publ Hlth Modeling Unit, New Haven, CT USA