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The Green Flu – Database: Episode 2

September 29, 2019


Hi, and welcome to Episode 2 of ValveTime Database, where we take an in-depth look at an element within
Valve’s games to determine the larger impact. In this episode, we’ll be taking a look at the
pathogen central to the Left 4 Dead series, commonly referred to as The Infection. This deadly infection sets up the events of the series, making most of the population of the
Eastern United States violent and animalistic, but is this pathogen more than just a simple illness? Officially known as The Green Flu, The Infection is a pathogen which causes
increased levels of aggression and decreased mental faculties in those who are infected. Despite its namesake, the Green Flu is more likely
to be some sort of rabies-like viral infection, with the name “Green Flu” being used by
the Civil Emergency and Defense Agency in an attempt to cover up the disease. Despite their best efforts, the graffiti in safe rooms shows that people are aware that this is no ordinary flu. Each of the symptoms of the disease has an
important impact on the gameplay of Left 4 Dead. Infected individuals appear pale with milky-white eyes, something which helps players to quickly differentiate
the cool, sickly pallet of the infected from the warm, lively tone of the survivors. The milky-white eyes serve a dual purpose in helping to make the infected appear extra creepy and disturbing, while also removing the need to draw and animate separate pupils for each of the zombies in the infected hordes,
thus improving system performance. The virus also drastically weakens the body’s
structure to the point where the infected can be easily dismembered, even by blunt weapons
such as baseball bats and crowbars. This helps give the series a large portion of its trademark gore. As revealed in The Sacrifice comic series, victims of the Green Flu suffer from severe hallucinations, causing them to see the survivors as demonic or monstrous. This may be part of what causes their erratic,
animalistic behavior and increased aggression. This behavior in-game helps to create a frantic tone, as common infected barrel down on you
at full force, shouting and coughing, barely able to keep their own balance while leaning into turns. It may also explain why the infected are easily distracted by loud noises and flashing lights
such as car alarms or pipe bombs. The age of most of the “living” infected encountered in both games ranges from young-adulthood to middle-aged. This may indicate that, like with most flus,
the people most susceptible to dying from the infection are infants, children, and the elderly. However, this might have been a conscious design choice by Valve to improve efficiency and avoid censorship. Most sicknesses transmit in one or more of five ways: droplet contact through coughing or sneezing; direct physical contact through touch; indirect physical contact such as touching a contaminated surface; airborne transmission; or fecal-oral transmission, usually through
contaminated food or water sources. From the evidence in the comic, it would appear that biting and vomiting
are the primary methods of transfer, something which is further supported in the gameplay, as common infected can be found coughing
and puking when in their idle state. However, the Green Flu may also be able
to change its transmission method, or it may exist in multiple, distinct strains. For example, it is suggested that the
sickness may be related to livestock. In the Left 4 Dead campaign Blood Harvest, and
Left 4 Dead 2 campaigns Dark Carnival and Swamp Fever, the player will encounter several deceased cows. These cows have had the skin on their heads removed, indicating that a rabies-like test has
been performed on the animals. Upon seeing the dead cow pile in Swamp Town, Rochelle sometimes mentions that the news
claimed the virus spread through livestock. [Rochelle from L4D2]
We heard reports that the virus spread through mammals, but I have no idea if that was true. Well, better safe than sorry, I guess. [James]
Given the rate at which the infection spreads, it would
seem that the infection can be airborne as well. This is confirmed in The Sacrifice comic series, where it was noted that the sickness was
“Sometimes airborne, sometimes not.” The variety of transmission methods suggests
that multiple strains of the virus exist. This could explain the rapid rate of mutation of the disease, in that one victim could become infected
with multiple strains of the virus. This could help explain the origin of the Special Infected. In The Sacrifice comic, it is revealed that immunity to the
Green Flu is passed down through the father’s genes. The most common theory is that the
gene which makes people resistant is a recessive allele on the X chromosome. A recessive allele will only produce its characteristic trait when paired with an identical allele from the other parent. This means that, for any female survivors to be resistant, they would need to receive the recessive
gene from both their father and mother. Therefore, the number of resistant males would be
the square of the number of resistant females, which would explain why the number of male survivors outnumbers the number of female survivors in both games. Unfortunately, resistance to the virus comes at a price. Survivors are not immune to the virus,
rather they are asymptomatic carriers of it, a fact revealed in the finale of the
Left 4 Dead 2 campaign “The Parish.” [James]
In the last part of the Left 4 Dead campaign No Mercy, players can find the dead body of what
may be “patient zero” of the Green Flu located on the fourth floor of the Mercy Hospital. He can be found in a room with a glass door covered
in caution tape and a biohazard warning sign. This is further hinted at in the game Payday: The Heist, where players revisit the Mercy Hospital in a campaign which Overkill Software created in collaboration with Valve. In this campaign, the players rob the Mercy Hospital, infiltrating the fourth floor to draw blood
from someone kept in quarantine. This heist opens up with a cryptic statement playing
off of the airborne nature of the infection, foreshadowing that the robbers may become infected and that they may be the reason the infection
escaped the hospital in the first place. However, we’re not entirely sure if the events
of Payday would be considered canon. Given that the heist ends with the military sending
fighter jets to shoot missiles at the hospital, some fans have suggested that the
government’s strong response may indicate that the nature of the virus was known
well before the events of Left 4 Dead, or that the virus may have been created or
engineered by the government as a weapon. This idea is further supported by the
existence of the special infected, given that, under normal evolutionary
conditions, it can take many years for multiple distinct strains of a virus to form. In total, there are 8 types of special infected: the Boomer, Hunter, Smoker, Witch, and Tank in Left 4 Dead, who are joined by the Charger,
Jockey, and Spitter in Left 4 Dead 2. It is unknown exactly what causes Green Flu victims
to mutate into one of the special infected, but it is clear that new types of special infected
continually mutate and develop as time passes. This is mentioned in the opening cutscene for Left 4 Dead, where Bill touches what appears to be a puddle of Boomer Bile and notes that it indicates the infected are “changing.” [Bill from L4D]
They’re changing. [Francis from L4D]
Dammit, Bill! Ugh, it stinks! [James]
This is further supported by the emergence
of the new special infected types encountered in Left 4 Dead 2, which takes place
just one week after the events of the first game. A poster found in one of the rooms in
The Vannah Hotel in the campaign Dead Center shows a pie-chart noting the infection ratio figures. Based on this chart, 63% of all Green Flu
victims become common infected, 4% become Spitters, 3% become Tanks,
6% become Boomers, 9% become Hunters, 7% become Smokers, 4% become Jockeys,
and 4% become chargers. The Witch is curiously missing from this chart. We won’t talk about the individual details
of each special infected in this episode, as we plan to make them the subject of an upcoming episode. In the beginning of Dead Center,
the first campaign in Left 4 Dead 2, the players can find a map created by CEDA which reveals that the epicenter of the infection was Philadelphia, Pennsylvania. This supports the patient zero theory
in that the fictional city of Fairfield, which serves as the setting for the
Left 4 Dead campaign “No Mercy,” is also located in Pennsylvania. The disease quickly spread from
Pennsylvania to Georgia in just 3 weeks, infecting most of the East Coast of the United States. Using the population of the East Coast — an estimated 58.28% of the total population
of the US, or about 180 million people — we can calculate the total number of people
infected with the Green Flu in that time. With only 22% of the population being resistant, combined with the quick rate of transmission as well
as the unprepared and ineffective evacuation efforts, and a nearly 100% probability of infection on
close contact with an infected person or carrier, it can be estimated that the total number of infected individuals could be up to a maximum of 140 million people. For comparison, between 1918 and 1920, the Spanish Flu killed an estimated 2.5% of the population of Earth, or around 50 million people over the course of 2 years. In epidemiology, the number of secondary
infections likely to be caused by an infected individual over time is
called its basic reproductive number — denoted as its R-nought. Generally the larger the R-nought,
the harder it is to control an epidemic. According to a report in the Oxford Journals, the R-nought for the Spanish Flu was
in the range of 1.2 to 3.0 overall, and 2.1 to 7.5 for community-based and confined settings. While there is not enough information
in the Left 4 Dead games and comics to accurately determine the Green Flu’s exact R-nought number, it would appear to be extremely high,
likely higher than any disease in history. While the Green Flu itself is clearly quite deadly, the Left 4 Dead games have proven that the
victims of the flu are effective killers too. Be sure to tune in for a future episode of ValveTime Database, which we’ll use to continue talking about the
Green Flu and the Special Infected themselves. Also, be sure to give us some suggestions for
future episodes in the comments below. Don’t forget to subscribe to our YouTube channel
and to follow us on Facebook and Twitter to stay up-to-date with all the latest Valve news and developments. Thanks for watching and bye for now.

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