RESUMEN
Vaccines produced in accordance with WHO formulas, differ in concentration from those used in United States according to FDA formulas. We aimed to compare the immunogenicity of both formulas. Infants who were 6 weeks old were randomly put into 3 groups to receive 3 doses of vaccines at 6 weeks, 3 months and 5 months of age. The vaccines consisted of Haemophilus influenzae type b vaccine, diphtheria-tetanus-pertussis and oral polio vaccine. Antibody levels for polyribosylribitol phosphate [PRP], tetanus, diphtheria and poliovirus were measured 1 month after the third dose of vaccines. Although diphtheria and tetanus antigens in the FDA formula are half the concentration of the WHO formula, anti-tetanus and anti-diphtheria antibodies were significantly higher. No difference was found between groups regarding oral poliovirus vaccine