We evaluated children (15-months old and older) with recurrent upper respiratory tract infections and normal
levels of immunoglobulins in serum for specific polysaccharide immunodeficiency using an enzyme-linked
immunosorbent assay method. Results showed that of 12 patients vaccinated with Act-HIB vaccine, one did not
develop specific antibodies to Haemophilus influenzae type b, demonstrating that such immunodeficiency is
present in Costa Rican children.