- Every year vaccines prevent the deaths of millions of children around the world.

In fact, the measles vaccine alone is estimated to have saved 21 million lives since the year 2000, but despite their success some parents are so afraid vaccines could be harmful that they are refusing to get their children immunized.

The World Health Organization has called the refusal to vaccinate a top threat to global health.

- Much of the anxiety about vaxxing safety stems from misinformation.

Fear over the measles, mumps, rubella vaccine for example can be traced to a single study.

A study so flawed it was later retracted.

So how did we get to a place where fears can jeopardize decades of progress in public health.

- [Female Reporter] Measles, the most contagious disease in the world spreading in hot spots around the country.

- [Narrator] In 2019, the United States hit an alarming new record.

- [Male Reporter] Measles surges to a 25 year high.

- [Narrator] It's the latest in a series of outbreaks that are drawing attention to a growing problem.

- Some people are deciding they're afraid of vaccines.

- [Narrator] The return of measles isn't just a danger to those who refuse to vaccinate.

Newborns who can't get inoculated and other vulnerable people depend on something called herd immunity to protect them.

Take whooping cough, it requires one of the highest percentages of the population to be immunized to prevent the disease from spreading, if not the consequences can be dire.

- The risk of whooping cough may sound like something from the past, but it's still very real.

Today, California reported more than 4200 cases, nine people have died all of them infants.

- [Narrator] For San Francisco mother, Mariah Bianchi those numbers are more than just statistics.

When her son was born in August 2005, as a nurse, she realized something was wrong.

- It was just like he was so lethargic and I knew that there was just something, I'm like I can't keep him awake.

We went to the doctor and she said, I want you to go to the hospital, as soon as he got there he went into cardiac arrest.

- [Narrator] What she didn't realize was that the immunity from her own whooping cough vaccine had worn off and her newborn was too young to be inoculated.

- And they started CPR right away for probably about 45 minutes or so.

As a nurse I'm thinking I know what that means your brain is not getting oxygen, your body is failing and the surgeon came out and he said his chance of survival is very low.

We made the most compassionate decision you could, but we just said, no, don't do it just stop.

- [Narrator] Dylan Bianchi died 17 days after he was born.

So how does society get to the point where some populations are left vulnerable.

Vaccines are one of the greatest achievements in public health.

- [Announcer] Dr. Jonas Salk discovered a vaccine that promises to wipe out childhood crippling and killing enemy, Polio.

- [Narrator] Polio, small pox, diptheria, no longer a threat in the US because of vaccines and in 2000, another watershed moment.

- The CDC reports the measles practically wiped out tonight in the United States.

- [Narrator] But that report proved overly optimistic.

- The measles vaccine has been so effective it doesn't seem like something we need to protect our children from.

You have this sort of fundamental paradox of vaccines that they have become a victim of their own success.

- [Narrator] Science writer, Seth Mnookin examines the fear about the measles vaccine in his book "The Panic Virus".

He says it can be traced to a moment in the late 1990s.

- The current vaccine scares and controversies that we're still dealing with today stem from a 1998 paper that appeared in The Lancet, a very respected medical journal published out of the UK.

- [Narrator] The paper written by Dr. Andrew Wakefield claimed there might be a connection between the measles, mumps, rubella vaccine and autism.

- In his press conference Andrew Wakefield stood up and said parents should not give their children the MMR vaccine, period, until we are able to get to the bottom of this.

- The MMR vaccination in combination that I think that it should be suspended in favor of the single vaccines.

- And what the media in the UK did was they ran with that.

- [Male Reporter] Doctors at the Royal Free Hospital believe they may have discovered a link between the combination vaccine and a bowel disease that can progress to autism.

- The notion that you would take a 12 person case study and make claims about a population as a whole, is ridiculous.

This paper was historically bad.

- [Narrator] It was later revealed that Wakefield also had a financial stake in trying to establish a connection between the MMR vaccine and autism.

Wakefield denies the allegations, but records show that he was paid more that 435,000 pounds.

- Andrew Wakefield was receiving money from a lawyer who was working with parents intent on suing vaccine manufacturers.

Perhaps the most shocking revelation is that he faked some of the data.

He's lost his medical license, The Lancet paper has been retracted, but he had very effectively positioned himself as a martyr.

And is some odd way, every piece of evidence that comes out against Wakefield, sort of solidifies his standing in the community that still pays attention to him.

- [Narrator] Follow up studies of hundreds of thousands of children, did not find any evidence that the MMR vaccine causes autism.

But early on, fears about vaccine safety took hold because complicated science proved difficult for public health institutions to communicate.

Case in point, their response when concerns were raised over a vaccine perseverative called thimerosal, which contains ethyl mercury.

- These children are getting mercury injected into their bodies with vaccines.

- That's right, mercury, a known neurotoxin.

- [Narrator] But ethyl mercury in thimerosal, is not the same as the toxic methyl mercury, which is found in fish and accumulates in the body.

Nevertheless, the Public Health Service and the American Academy of Pediatrics recommended thimerosal be removed and their messaging backfired.

- [Female Reporter] In 1999, health officials denied a link between vaccines and the autism epidemic yet urge vaccine makers to take out the mercury just to be safe.

- What the American Academy of Pediatrics said is we're recommending this step so we can make safe vaccines even safer.

As a parent, if you tell me something's safe, I don't think that's on a sliding scale.

I assume that if you say it's safe, it is safe for my child.

It is not safe, safe or safest.

There's almost two languages here.

There's the language of science and then there's English.

And in the language of science, you have these signifiers like, to the best of our knowledge, as far as we know.

- Based on the available scientific evidence.

- Because you can't say anything with 100%, you can't prove a negative.

And so when scientist speak, in their language, and the rest of us translate that into English, it sounds like they're saying something very different than they're saying.

- Based on what we know right now, we don't think that there is an association.

- But that's not saying with 10% certainty, there isn't one.

- That is saying that based on the evidence that we have right now, we don't think that there is one.

- Either because the reporter doesn't understand what's actually going on, or because they are looking to generate a story, they then take that and make it seem as if the scientist is saying I think there's a possibility that vaccines do cause autism when, in fact, that's not it at all.

- News organizations should exercise judgment about what goes out over their air.

- [Narrator] Brendan Nyhan is a professor at the University of Michigan who studies how misinformation spreads and the role of the media.

- What's particularly important is to think about the overall scientific consensus.

Where is the weight of the evidence and is our reporting reflecting that or not.

That's what's often gone astray in the vaccine debate.

- It's time for everyone to redirect the questions towards finding the cause of autism.

It is not, however, vaccinations.

- Controversial subject, Nancy.

- Not controversial subject.

- But controversial for parents who still believe - It is not controversial Mat, it's time for kid's to get their vaccines - If it weren't controversial - Everyday people can't be fact checkers for every story about vaccines, and when journalist don't give people the weight of the scientific evidence they're letting them down.

- When she got her vaccinations, she ran a low grade fever, she had a little rash and then she stopped talking.

- [Narrator] A false sense of balance was also created when scientific evidence was equated with people's personal experiences.

- Reporting fell into this, on the one hand, on the other hand fallacy.

This notion that if you have two side that are disagreeing, that means that you should present both of them with equal weight.

- We vaccinated our baby, and something happened, that's it.

- Jenny McCarthy has had more to do with popularizing the notion that vaccines are dangerous than any other single person in the United States.

- We begin, of course, with Jenny McCarty, the actress and entertainment personality, her son, Evan, has autism.

She is very smart, she's telegenic.

- Look it, it's plain and simple it's [Beep] - No it's - Yes it is!

- Excuse me.

- When I look at clips of her, it's a completely unfair fight.

- My science is named Evan, he's at home.

That's my science (crowd clapping and cheering) - Jenny McCarty has said many times and often times very loudly that, you know, her child is her scientific fact.

Any scientist or any science reporter who's familiar with how science works would say that no, any one person is an anecdote and the plural of anecdote is not data, you know.

It's just a story.

- [Narrator] But stories are powerful.

While vaccination rates are high nationwide, there are some religious enclaves and communities of well educated, upper middle class people, where vaccine hesitancy runs strong.

- I was interviewing and epidemiologist and he said oh, yeah, we completely know we were going to have communities that have issues with vaccine uptake.

We take a make and stick a pin wherever there's a Whole Foods and draw a circle around it and that's where we're going to have problems.

He was obviously being facetious.

- [Narrator] Exasperated health officials are trying to come up with new ways to communicate with the public.

Brendan Nyhan conducted a study and watched how hesitant parents reacted when they were shown information from the CDC website, stating there is no evidence the MMR vaccine causes autism.

- The good news was, it did cause parents to be less likely to believe in the myth that the MMR vaccine causes autism.

The bad news is, however, that it made them less likely to say that would vaccinate a child.

Which is precisely the opposite of what we would hope to see.

What we found is, that telling people the correct information wasn't actually effective.

[Narrator] That highlights how susceptible people can be to misleading information.

A recent investigation found that internet trolls from Russia, targeted Americans and used the topic of vaccines to create division.

Some states are weighing in and taking action.

- California now has one of the strictest school vaccination laws in the country.

- [Female Reporter] There will no longer be religious exemptions.

There we no longer be personal belief exemptions.

- [Narrator] After an outbreak linked to Disneyland in 2014, California enacted one of the toughest vaccine laws in the country.

Still, some parents are trying to circumvent the law.

For Mariah Bianchi, the notion of leaving some people vulnerable is hard to understand.

What does it takes?

How many times do you have to tell people or talk about it?

We all have a role in helping each other to protect each other.

A vaccine preventable disease should not have killed my son.