Almost every day seems to bring more bad news about the Zika virus: babies born with malformed brains; adults suffering the progressive paralysis of Guillain-Barré syndrome; Americans diagnosed after traveling to the tropics; active transmission of the disease in U.S. territories. Several companies are working on a vaccine, but primarily because of regulatory requirements none is likely to become commercially available before the end of the decade.

Last month President Obama announced that he will ask Congress for $1.8 billion...