1. Division of Viral and Rickettsial Diseases, National Center for Infectious Diseases, Centers for Disease Control and Prevention (CDC), 1600 Clifton Road, Atlanta, GA 30333, USA.
2. Caribbean Epidemiology Centre (CAREC) Laboratory, Pan American Health Organization (PAHO), 16-18 Jamaica Boulevard, Federation Park, Port-of-Spain, Trinidad and Tobago.
3. Division of Vaccines and Immunization, PAHO, 525 Twenty-Third Street, N.W., Washington, DC 20037, USA.
4. Ministry of Health, Avenida San Cristóbal esquina Tiradentes, Santo Domingo, Dominican Republic.
5. Ministry of Public Health, Port-au-Prince, Haiti.
6. Vaccine Preventable Disease Eradication Division, National Immunization Program, CDC, 1600 Clifton Road, Atlanta, GA 30333, USA.
7. PAHO, Calle Pepillo Salcedo, Plaza de la Salud, Santo Domingo, Dominican Republic.
8. PAHO, Number 295 Avenue John Brown, Port-au-Prince, Haiti.
9. Department of Virology II, National Institute of Infectious Diseases, Toyama 1-23-1, Shinjuku-ku, Tokyo 162, Japan.
10. Polio Laboratory, National Institute of Public Health and the Environment (RIVM), Antonie van Leeuwenhoeklaan 9, 3720 BA, Bilthoven, Netherlands.