[vetvetdoug]

Sometimes in an antigenic drift situation, the immunological response makes immunity toward the disease first encountered and cannot recognize the new infection. If the Panama/Fujian situation is such, then we are in deep...well you know. The body can make antibody toward several diseases at the same time, only if it recognizes them.

[Judith Anne]

True. But cowpox protects against smallpox, both are viruses.