By Mark Pendergrast

As I watched the blockbuster bio-thriller Contagion, I was struck by how realistic it was in many ways. That isn’t surprising, since many epidemiologists, including those from the Centers for Disease Control and Prevention (CDC) in Atlanta, served as advisors. The film was based on a simple premise. What if a new, deadly virus that kills one out of four people it infects were also easily transmissible from human to human?

I knew more about the subject than most people in the audience, because I spent five years researching and writing Inside the Outbreaks, a history of the Epidemic Intelligence Service (EIS). EIS officers have served as the front-line CDC disease detectives since the organization was founded in 1951 in the midst of Cold War fears of bioterrorism. In the film, EIS officer Erin Mears, played by Kate Winslet, is sent to investigate the epidemic in Minneapolis, where she contracts the disease herself and dies a few days later. In reality, only one EIS officer has died in the line of duty, and that was when a terrorist blew up an airplane during the Biafran War in Nigeria. But there have been several close calls, as EIS officers have caught the diseases they were investigating.

Winslet’s portrayal of an EIS officer is essentially accurate, though she would not have been sent alone to handle such a major outbreak. More than half of EIS officers are female nowadays. They usually enter the two-year program in their early thirties, often with a masters in public health. Most are, like the Erin Mears character, compassionate, driven, idealistic, and courageous.

There are four main lessons we can glean from the film.

Lesson 1: We are an invasive species. At the film’s end, a bulldozer dislodges infected fruit bats (the source of the pandemic virus) from tropical trees. It is true that as people invade and disturb habitats, we are more likely to encounter new pathogens. That’s probably how the AIDS epidemic began, with transmission of a simian virus to humans. We are, after all, animals, living in a complex web of other living beings, so it isn’t surprising that zoonoses (diseases that spread from other animals to humans) are so common. And as humans proliferate — there will probably be 10 billion of us swarming the earth by 2050 — we offer a tempting target for infectious diseases.

Lesson 2: Bioterrorism is overrated. In the movie, officials of the Department of Homeland Security tell CDC epidemiologist Ellis Cheever that they suspect the new virus is a bioterror weapon intended to disrupt the Thanksgiving weekend and spread more quickly as people travel to be with their families. Cheever informs them, “Someone doesn’t have to weaponize the bird flu — the birds are already doing that.” Indeed, fears of bioterrorism, which helped to create the Epidemic Intelligence Service in the first place, are overblown. Yes, bioterrorists could spread deadly pathogens such as anthrax, but mad scientists are less likely to create a deadly viral mutation that is easily transmissible between humans. Nature is far better at such achievements. The next pandemic will not be man-made, at least not intentionally.

Lesson 3: People panic. The film is at its strongest in showing how people are likely to react during a pandemic when insufficient drugs or vaccines are available. How will they be distributed? Who decides who will get them first? What kind of looting and violence is likely to ensue? Contagion offers a chillingly plausible scenario. We are woefully unprepared for such panic-driven behavior.

Lesson 4: Rumors on the internet can kill. In Contagion, blogger Alan Krumwiede, played by Jude Law, convinces 12 million frightened internet followers that the government can’t be trusted. The CDC is lying, he writes. Their new vaccine is useless or even harmful. Instead, Krumwiede promotes a homeopathic remedy made from the forsythia plant. He pretends that he has contracted the virus and that he cured himself, thereby making himself wealthy, even as he misleads the public.

These are important lessons, yet Contagion also falls short in a number of ways. While it is far better than most Hollywood biopics, it focuses more on the social consequences of a worst-case scenario than on the science.

For one thing, it doesn’t teach us much about how epidemiologists work, probably because such logical, seemingly plodding methodology doesn’t suit the media. I have some painful personal experience in this regard. When Inside the Outbreaks was published in 2010, it was optioned for a television series, and an experienced Hollywood writer was hired to script a pilot show, in which a platoon of soldiers in basic training dropped like flies. It turned out to result from the intentional poisoning of beef jerky in a vending machine at a bar. The EIS officer in the script figured it out purely by serendipity.

I objected: “What is startlingly missing from the script is the EIS officer asking what they ate. This is very likely to be a foodborne outbreak of some sort. So she is looking for a common food. She should be doing a case-control study, asking the sick men what they ate and where they were, as well as soldiers who didn’t get sick but were as similar as possible in all other ways (i.e., who went on the same march, were in the same barracks, etc). Then when the case-control study pointed to the bar, but not to a particular food, she could have her Eureka moment, seeing the vending machine, finding out what was in it, and going back and redoing the case-control study with the right questions about whether they ate anything from the vending machine, and what it was. One of the vital points of epi is not only to use the right methodologies but to ask the right questions.”

The script writer responded: “It is to be assumed she asked what they ate, since she’s also asking deeply idiosyncratic and minute questions. But honestly, ‘What did you eat?’ is very boring and had to be avoided.” The pilot show was never made. Although I wanted my book to be the basis of a TV show, in a way I was relieved.

To his credit, Scott Burns, who wrote the screenplay for Contagion, included some explanation of how the virus was transmitted (by breathing droplets or by touching the same objects as those infected), but the movie did not focus on epidemiology, the methodology of disease detectives. Only at the end of the film do viewers get a quick glimpse of how the virus was transmitted, from fruit bats to pigs to people. Somewhere in the middle of the movie, there is a glimpse of the phrase “Nipah virus” on a CDC document, but otherwise moviegoers would have no idea that this is in fact the real-life virus on which the fictional MEV-1 virus was based. And the film offers no clue as to how anyone figured out its origin or transmission route.

In Inside the Outbreaks, I wrote about the first terrifying Nipah virus epidemic that began in 1998 in Malaysia with pigs who began to twitch, cough, bite at their bars, and lose their footing. Their urine turned bloody. Then they collapsed and died. Pig farmers developed fevers, becoming lethargic and disoriented. Some fell into a coma and died. A desperate farmer advertised on the Internet, selling sick swine on the cheap to farms 50 miles away, where over 200 farmers contracted the disease. When CDC labs found a new virus in spinal fluid from patients, they named it Nipah virus, after a village where the fire sale pigs had been sent, and it was designated a Biosafety Level 4 pathogen, equivalent to Ebola.

“People left their farms, their pigs, everything they owned. Whole villages just fled,” recalled EIS officer Mike Bunning. The outbreak was finally brought under control at the end of May 1999, by which time a million pigs had been sacrificed and 108 out of 280 identified human cases had died. The EIS case-control study indicated that direct contact with sick pigs was a primary risk factor.

The EIS officers suspected that Malaysian bats might serve as the reservoir for Nipah virus and helped to capture a variety of them, including the giant fruit bats known as flying foxes. Sure enough, Nipah antibodies were eventually found in the flying foxes. A dead bat or its feces might have fallen into a feed lot, or bats may have dropped contaminated, partially eaten fruit into pig pens.

In the ensuing years, Nipah virus jumped to Bangladesh and neighboring parts of India, often killing 75 percent or more of its victims, but there was no evidence of person-to-person transmission — it always required contact with a pig. Mike Bunning thought the actual mortality in Malaysia may have been near that figure, since many Chinese laborers who died were buried secretly to avoid the slaughter of their pigs. “If Nipah had been communicable between humans,” Bunning observed, “The world as we know it today would be different.”

I don’t know if anyone involved in Contagion read my book, but Bunning’s final chilling comment summarizes the basic premise of the film. Rather than a 75 percent mortality rate, the movie assumes a 25 percent rate, but that is still appallingly high. The film shows how quickly such a contagion could spread in the jet age.

Yet this doomsday scenario is unlikely to occur, though it is still possible. The most horrific viruses, such as Ebola or Nipah, tend to be dead ends in human beings. They evolved in order to take advantage of other hosts, such as fruit bats. It is a freak of nature that humans happen to succumb so quickly and horribly. If these viruses mutate in order to become easily transmissible between humans, they are also likely to become far less lethal. Why? Darwin told us. Evolution favors survival, and a virus that kills off too many hosts will not survive for long. Still, a lot of people could die before the virus fully adapted to humans.

“Successful” pathogens don’t kill the majority of their victims. They cause communicable diseases such as polio, diphtheria, tetanus, pertussis, influenza, yellow fever, measles, rubella, rabies, hepatitis, meningitis…. the list goes on. All of these bacteria and viruses have something else in common. All have vaccines that can save lives. That is why, to me, the most upsetting part of Contagion was not the virus itself, but the con artist Krumwiede who profits by scaring people away from an effective vaccine.

We don’t need a fictional pandemic to demonstrate this kind of scenario. It has been happening for years, as rumors that vaccines cause rather than cure diseases are rampant on the Internet. Although all vaccines cause adverse reactions in some people, the truth is that they have prevented millions of people (mostly children) from dying. Because of a vaccine, smallpox, an ancient killer, has been eradicated.

Yet paranoia over government-sponsored health programs has prevented many people in the United States and elsewhere from protecting themselves and their children. As long as enough people are immunized, infections are unlikely to spread rapidly, but as a large susceptible population develops, epidemics, illness, and deaths become inevitable.

It is impossible to prove a negative, so one cannot prove that vaccines do not cause autism or other ailments. Epidemiology is a science of probability, not proof. But an overwhelming array of epidemiological studies provides evidence that vaccines do not cause autism or the other ailments that fear-mongers claim. So let me end this essay with a plea for support for vaccinations. Anti-vaccine misinformation on the Internet is more prevalent and powerful than the staid official policy presented on the CDC website. But there are other well-informed websites about current dangers from vaccine-preventable diseases, such as Meningitis Angels, Parents of Kids with Infectious Diseases, and Families Fighting Flu. In addition, Voices for Vaccines provides science-based information. Also, check out the well-researched, informative books by pediatrician and vaccine specialist Paul Offit. The fact that Dr. Offit has received hate mail and death threats for telling the truth and trying to save lives is evidence of the passionate misinformation out there.

Mark Pendergrast is the author of Inside the Outbreaks: The Elite Medical Detectives of the Epidemic Intelligence Service (which was featured in the ScienceBlogs Book Club) and several other books, including, most recently, Japan’s Tipping Point. Email and book information is available at his website.