To prepare a vaccine candidate , a previously described 30 nucleotide deletion ( Delta30 ) in the 3 ' untranslated region of DEN-4 has been engineered into the DEN-2 isolate .
O O O O O O O O O B-SequenceVariant I-SequenceVariant I-SequenceVariant O B-SequenceVariant O O O O O O O O B-OrganismTaxon O O O O O B-OrganismTaxon O O