[1] Emory Univ, Rollins Sch Publ Hlth, Atlanta, GA 30322 USA
[2] Univ Witwatersrand, Resp & Meningeal Pathogens Res Unit, MRC, Johannesburg, South Africa
[3] Univ Witwatersrand, Dept Sci & Technol, Natl Res Fdn Vaccine Preventable Dis, Johannesburg, South Africa