Phalanx was a vaccine for Rabies that was developed by Breckenridge Scott during World War Z. However it was marketed as being effective against Solanum and able to prevent people from turning into zombies. The revelation that Phalanx was ineffective against Zombies was an important trigger to the Great Panic.
When the first publically recorded zombie outbreaks were reported in South Africa, the infection was referred to as "African Rabies." Scott, who had already made large sums of money selling placebo products, saw the outbreak as another way to obtain a large source of money. The product was tested against Rabies and was marketed as such, allowing it to pass FDA testing. Since the majority of the American population believed that the zombie outbreak was a new strain of Rabies they were fooled into thinking Phalanx would be an effective countermeasure.
While Phalanx was effective against Rabies, it did nothing to stop the spread of Solanum. However during its first year of release it eased the minds of the population and stimulated the economy, ending the recession. Bites by Quislings fooled even more people into thinking that Phalanx worked against Zombies. However as the number of Zombies began to rise it became clear that Phalanx was not working and a newsreporter finally revealed that Phalanx was completely ineffective against Zombie bites. This resulted in the outbreak of the Great Panic, creating chaos and weakening the ability of the United States to resist the zombies and maintain order. Scott fled to a research station he leased from Russia in Antarctica, where he has remained ever since.