impediments to development may exist or arise at any point in this pathway ( e.g. , multiplicity of serotypes , inability to cultivate the pathogen , multistage life cycles with multiple antigens , unpredictability of epidemics , inadequate knowledge of pathogenesis and immunity , fear of gene splicing , need for an adjuvant , and lack of profitability ) .
C0003320
antigens
C0020964
immunity