Phalanx was the drug that was dubbed "the African Rabies vaccine". Created by Breckenridge "Breck" Scott, a corrupt pharmaceutical developer, he quickly made a fortune. Scott jumped on the idea of a vaccine almost as soon as reports of "African Rabies" outbreaks came out of South Africa. In a few months, his company had developed a creditable vaccine for marketing, naming it Phalanx after the powerful defense formation of the ancient Greeks.
It all turned out to be a hoax drawn up to make money. Although it was a real vaccine for actual rabies, it was nothing more than a placebo against the zombie virus Solanum. In fact, it had never been tested against Solanum at all. Nonetheless, the fact that it was harmless to use meant it was approved by the US Food and Drug Administration. Technically, Phalanx was never actually marketed as an "anti-zombie virus vaccine"; it was openly described as a vaccine against "rabies", and it did work, so it passed FDA testing. The problem was that people wanted an anti-zombie vaccine at the same time that they refused to believe that zombies existed.
One of the good things that came from this so-called miracle drug was it stimulated the United States of America's economy and put more value behind the American greenback. This was due to the high number of second-hand knockoff drugs and the various "anti-viral" products with the Phalanx label on it. Phalanx sales saw an even bigger boom when a Phalanx user in Florida claimed to have been bitten by a zombie and had survived thanks to the vaccine (it was later revealed that he was in fact bitten by a quisling, not an actual zombie, hence his survival).
This bull market was quickly shot dead when spring rolled around and zombies began defrosting, and attacks began rising sharply. A single female reporter then broke the news to the world that not only was the zombie virus not rabies, but that Phalanx was absolutely no defense at all. This is most likely what set off The Great Panic, during which Breckenridge pulled an Enron-esque investment fraud, fleeing the U.S. with millions, if not billions, of dollars of his investor's money. Scott eluded authorities easily thanks in part to the turmoil that now engulfed the world.
Scott eventually bought refuge at the Russian-owned Vostok research station in Antarctica, and he hasn't left it since the Great Panic. To this day Scott denies any and all responsibility for any of his actions, and is confident that as long as he can keep paying, the Russians will continue to offer him political protection. Numerous vengeful authorities, particularly the IRS, have been negotiating with the new Russian government since the end of WWZ to end Scott's lease at the station, and indications from American officials suggest that the Russians may be willing to oblige in the very near future.
Scott's half-mocking, half-serious rationalization for why he feels no guilt about Phalanx, is that he could not possibly have gotten Phalanx on the market as just one man. The government wanted there to be a vaccine so people would calm down. People on the street wanted a miracle-cure. Moreover, major news organizations wanted Phalanx to work, because it was big news. In short, people were hoping for a quick fix to the virus, hoping it actually was just a particularly bad new strain of rabies. Multiple official government or news agencies could easily have exposed Scott at several levels during Phalanx's production, but they didn't.