As Fevaxyn FeLV is a whole virus vaccine it presents a number of potentially antigenic proteins, in combination with an aqueous adjuvant. The antigen was selected on its immunogenic property. The FeLV subgroup-A Rickard strain is known to cause the typical symptoms of Feline Leukaemia. Subgroup-B and subgroup-C are recombinations of subgroup-A with cat genome sequences. Subgroup-A and B are part of Fevaxyn FeLV vaccine antigen and should also immunise against subgroup-C.

Fevaxyn FeLV is fully compatible with Katavac CHP so all antigens can be administered by one injection.