An immunogenic agent which comprises a killed strain of Burkholderia pseudomallei, or a combination of components thereof which combination produces a protective immune response in an animal to whom it is administered, and which comprises at least two members selected from the group consisting of (i) a lipopolysaccharide of Burkholderia pseudomallei, (ii) a capsular polysaccharide of Burkholderia pseudomallei and (iii) a protein of Burkholderia pseudomallei or an immunogenic variant thereof or an immunogenic fragment of either of these, or a nucleic acid which expresses said protein, immunogenic variant or immunogenic fragment thereof in a host animal; for use in the prevention or treatment of infection by Burkholderia pseudomallei and/or Burkholderia mallei.