(S (S (BASENP (NNS Scientists)) (VP (ADVP (RB also)) (VP (VBP say) (SBAR (IN that) (S (NP (BASENP (JJ current) (NNS vaccines)) (VP (VP (VBN used) (PP (IN in) (BASENP (NNS birds)))) (PP (IN for) (BASENP (DT the) (JJ H5N1) (NN virus))))) (VP (MD might) (VP (VB have) (VP (VBN caused) (S (BASENP (DT the) (JJ new) (NN strain)) (VP (TO to) (VP (VB develop)))))))))))) (PERIOD .))