[1] Charles River Med Grp, 155 King George Ave, Harare, Zimbabwe
[2] RTI Int, 3040 East Cornwallis Rd, Res Triangle Pk, NC 27709 USA
[3] Univ Witwatersrand, Fac Hlth Sci, Wits Vaccines & Infect Dis Analyt VIDA Res Unit, ZA-2000 Johannesburg, South Africa
[4] Columbia Univ, Inst Social & Econ Res & Policy, IAB 118th St, New York, NY 10025 USA
[5] Columbia Univ, Vaccine Informat Network, 533 W 218th St, New York, NY 10032 USA
[6] Columbia Univ, Vagelos Coll Phys & Surg, Dept Pediat, New York, NY 10032 USA
[7] Univ Zimbabwe, Fac Med & Hlth Sci, Dept Primary Hlth Care Sci, Internal Med Unit, POB A178, Harare, Zimbabwe