PBS's "Nova" kicks off its fall season on Sept. 10 with "Vaccines: Calling the Shots," and the subject couldn't be more timely. Epidemics and the threat they pose are making front page news. The Ebola virus outbreak in Africa is grabbing headlines and raising fears, and there's a more immediate threat here at home: the resurgence of preventable diseases once thought to be eradicated. Measles, mumps and whooping cough are on the rise, due to the decision by some parents not to vaccinate or to delay inoculating their children. This can have devastating public health consequences, as the film explains.

"These parents are making a bad and misinformed choice that puts not only their children at risk, but those with whom their children come in contact at risk," says Dr. Paul Offit, pediatrician and chief of the Division of Infectious Diseases and director of the Vaccine Education Center at the Children's Hospital of Philadelphia, who was interviewed in "Vaccines."

That was the same point Australian science television filmmaker Sonya Pemberton intended to make when she started working on the project nearly five years ago, but she was surprised to find so much anti-vaccination dissent. To present both sides of the issue, she spent a year interviewing parents with varied opinions to present all sides of the issues, including individual stories, scientific history, the mechanics of how vaccines work, and an overall risk assessment.

"We acknowledge the fear and the concerns. We take people on this journey so that they can come to the conclusions that the science clearly supports. All medications carry some degree of risk, but vaccines work and save millions of lives," says Pemberton.

That's the message Offit emphasizes with some frightening statistics. "There's 20 million cases of measles in the world every year and 120,000 deaths. As of mid-July there were 565 cases of measles [in the U.S.], more than we've seen in 20 years. We had almost 50,000 cases of whooping cough in 2012 and 20 deaths. Between 75 and 150 children die every year from influenza. During pandemic years like 2009, it was 1,200. We're seeing outbreaks the likes of which we haven't seen in a couple of decades."

Why is this happening? "Because people don't fear the diseases. Vaccines are a victim of their own success," says Offit. "I think we're compelled more by fear than by reason," he adds. "When you lower the immunization rates these diseases are going to come back, but people don’t believe it until they see it."

Misinformation is a key issue, he continues. "Those who choose not to vaccinate can find like-minded misinformed people on the internet to support their point of view," blaming vaccines for everything from allergies to autism, diabetes and multiple sclerosis. "All the evidence supports the notion that vaccines don't cause these problems. But people who are more scared of the vaccine than they are of the disease choose not to believe the data."

He believes it will take an outbreak to change mindsets, because "people are much less compelled by reason than fear, and they don't fear these diseases. Those who don't learn from history are condemned to repeat it." The most contagious diseases like measles, mumps and whooping cough are the likeliest candidates, but diphtheria and polio are also possible.

Then there's influenza, which kills thousands of people every year despite the wide availability of the flu vaccine. "Every year the virus changes enough so the vaccine from the previous year doesn't prevent it, that's why you get a yearly flu shot. When it changes so dramatically that most people haven't seen it before, that's when you get a pandemic strain. That occurs every 20 years or so," Offit says, noting that at Children's Hospital, flu shots have been mandatory for all healthcare workers since 2009. "We didn't consider it a right to catch and transmit potentially fatal infections in our hospital."

There’s no such mandatory compliance for schoolchildren. Laws vary by state and community, and there are various exemptions including religious and medical reasons. "Of the 300 million people in this country, 500,000 can't be vaccinated. These include children getting chemotherapy for cancer or immunosuppressive therapy for a variety of diseases like juvenile rheumatoid arthritis, and people who are in remission from leukemia," says Offit.

These people with compromised health "depend on the herd, those around them, to protect them. So when people don't vaccinate they put those children at risk. When I was in 10th grade, there was a boy in my class who had leukemia. None of our parents would have sent us to school unvaccinated and put this boy at risk. We owed him that, because we are all in this together. When parents make a choice to put their children at risk unnecessarily, it’s really hard to conscience."

When people ignore this precept and weaken the herd's immunity, Offit observes, everyone becomes susceptible, especially with world travel making it easy for viruses to cross borders. "An unvaccinated person goes to a country like the Philippines, which last year had tens of thousands of cases of measles and 41 deaths, brings it back to the United States, and then there's enough children that are unvaccinated that it then spreads locally," he posits a scary scenario. "There are three countries that never eliminated polio and 20 countries that are now dealing with it. Do I think people with asymptomatic polio are coming into this country? Absolutely. If herd immunity gets low enough, we could see cases of polio in this country. And maybe that will be what finally changes the story."

There is good news, however. New vaccines are on the way that include broader form of the HPV (human papillomavirus) vaccine later this year, a vaccine to treat a relatively rare from of meningitis early next year, and an RSV (respiratory syncytial virus) vaccine soon, according to Offit, the co-inventor of the vaccine for rotavirus, which is responsible for the deaths of about 435,000 infant deaths each year around the globe.

Another positive: "pushback" from pro-vaccination parents who are speaking out, saying, "By choosing not to vaccinate you're putting my child at risk. Ultimately I hope we will stand up for the children who need the herd to protect them. Medicine is hard enough — there's so much we don't know and can't do," Offit says. "This we know and can do."

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Should you inoculate your child? 'Nova' documentary explores contentious issue
PBS "Nova" documentary "Vaccines: Calling the Shots" explores both sides of the contentious issue.