1. Influenza Division, Centers for Disease Control and Prevention , Atlanta, Georgia , USA
2. U.S. Naval Medical Research Unit No. 6 , Bellavista , Peru
3. Instituto Nacional Materno Perinatal , Lima , Peru
4. Hospital Nacional Docente Madre Niño San Bartolomé , Lima , Peru
5. Hospital Nacional Arzobispo Loayza , Lima , Peru
6. Hospital Nacional Dos de Mayo , Lima , Peru
7. Abt Associates, Inc. , Atlanta , Georgia , USA