Presently, 21 serotypes have been identified and have no obvious cross-protection among serotypes.But these 21 serotypes have a conservative region in the Ompa and have immunity nature.

• RA为革兰氏阴性小杆菌，至今国际上公认的血清型有21种，各血清型之间并无显著的交叉保护，这就为免疫预防增加了难度。