In this same study, vaccine efficacy against pertussis with paroxysmal cough was >70% when levels of FIM2/3 antibodies were high (>5 enzyme-linked immunosorbent assay [ELISA] units [EU]) compared with an efficacy of 46.1% when antibodies to PT were high, indicating that anti-FIM antibody may provide a possible correlate of protection against pertussis [52]. This evidence concerns the gene F2 and pertussis.