Sanofi’s dengue vac­cine slams in­to a safe­ty is­sue, trig­ger­ing a $120M write-off and evis­cer­at­ing old block­buster pro­jec­tions

Sanofi spent $1.5 bil­lion over about 20 long years to de­vel­op its dengue vac­cine, be­liev­ing that it had a block­buster prod­uct head­ed to a mas­sive glob­al mar­ket.

But their in-house de­vel­op­ment team missed some­thing im­por­tant.

On Wednes­day, Sanofi $SNY said that their in­ves­ti­ga­tors had de­ter­mined that Deng­vax­ia pre­sent­ed a re­al threat to pa­tients who were vac­ci­nat­ed against dengue with­out hav­ing first been ex­posed to it. As a re­sult, these sub­jects could ex­pe­ri­ence a sig­nif­i­cant­ly worse re­ac­tion when ex­posed to a new in­fec­tion — with their body re­act­ing to the first ex­po­sure as if it were the sec­ond, due to the vac­ci­na­tion.

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