New York (CNN Business) Amid a growing measles outbreak in the United States, the role of powerful tech companies like YouTube and Facebook in spreading vaccine misinformation is under heavy scrutiny .

But there is another massive platform offering spurious anti-vaccination content to people seeking information, a review by CNN Business reveals: Amazon, the world's largest online marketplace. And, asked about it, an Amazon spokesperson only pointed CNN Business to the company's content guidelines page , which says the following: "As a bookseller, we provide our customers with access to a variety of viewpoints, including books that some customers may find objectionable. That said, we reserve the right not to sell certain content, such as pornography or other inappropriate content."

A recent search for "vaccine" onyielded a search page dominated by anti-vaccination content. Of the 18 books and movies listed on the search page, 15 contained anti-vaccination content. The first listing was a sponsored post — that is, an ad for which Amazon was paid — for the book "Vaccines on Trial: Truth and Consequences of Mandatory Shots" by Pierre St. Clair, which Amazon was also offering for free to Kindle Unlimited subscribers.

Among the search results were books and movies that made their anti-vaccination stance clear in their titles, like the movies "We Don't Vaccinate!" and "Shoot 'Em Up: The Truth About Vaccines."

But perhaps more disturbing from a public health and misinformation perspective, there were also books that people simply searching for information — new parents, for instance — could mistake for something offering neutral information accepted by the public health community, like "Miller's Review of Critical Vaccine Studies: 400 Important Scientific Papers Summarized for Parents and Researchers" and "The Vaccine-Friendly Plan: Dr. Paul's Safe and Effective Approach to Immunity and Health — from Pregnancy Through Your Child's Teen Years," both of which featured Amazon's "Best Seller" tag.

Amazon also offers its Prime members a number of anti-vaccination movies for free viewing on Prime Video, like "VAXXED: From Cover-Up to Catastrophe," which was dropped from the Tribeca Film Festival in 2016 following a public outcry.

Its director, Andrew Wakefield, has played a central role in spreading anti-vaccine propaganda. Wakefield was part of a team of researchers who published a 1998 study that became the basis for the anti-vaccination movement. The study was later retracted and Wakefield was stripped of his medical license.

Amazon declined to comment on how much it was paid for the ad for "Vaccines on Trial" or whether it has accepted money to promote any other anti-vaccination books or movies.

CNN Business' findings upset at least one expert in the field.

"It's dirty money," Dr. Paul Offit, a professor of pediatrics at the Children's Hospital of Philadelphia and a prominent proponent of vaccination, said of the ad Amazon ran. "What Amazon is willing to do is, for a price, put bad information out there. They should be held accountable. ... There aren't two sides to the science. Vaccines don't cause autism, diabetes, MS, or any of the other chronic disorders anti-vaccination proponents claim."

Tech companies under fire

Facebook FB Google GOOGL Earlier this month, Rep. Adam Schiff, a Democrat from California, sent an open letter toand, which owns YouTube, expressing concern that the companies are "surfacing and recommending" anti-vaccination content that has caused "declining vaccination rates which could reverse progress made in tackling vaccine-preventable diseases."

"The algorithms which power social media platforms as well as Amazon's recommendations are not designed to distinguish quality information from misinformation or misleading information, and as a result harmful anti-vaccine messages have been able to thrive and spread," Schiff said in a statement to CNN Business. "Every online platform, including Amazon, must act responsibly and ensure that they do not contribute to this growing public health catastrophe."

In a statement sent to CNN earlier this month, a Facebook spokesperson said it has "taken steps to reduce the distribution of health-related misinformation on Facebook, but we know we have more to do."

"We're currently working with outside experts on additional changes that we'll be announcing soon," the spokesperson said.

Critics have also pointed to YouTube's practice of recommending videos based on watch history as leading users to anti-vaccination misinformation. The Guardian recently discovere d an anti-vaccination video was recommended alongside a Mayo Clinic clip on the measles vaccine.

"Misinformation is a difficult challenge and any misinformation on medical topics is especially concerning," a YouTube spokesperson told CNN Business on Monday.

"We've taken a number of steps to address this including surfacing more authoritative content across our site for people searching for vaccination-related topics, beginning to reduce recommendations of certain anti-vaccination videos and showing information panels with more sources where they can fact check information for themselves. Like many algorithmic changes, these efforts will be gradual and will get more and more accurate over time."

Pinterest also recently announced it had blocked all vaccine searches from its platform in a temporary ban.

Measles outbreak linked to unvaccinated people

In February, the CDC reported 159 measles cases had been confirmed in 10 states, including California, Colorado, Connecticut, Georgia, Illinois, Kentucky, New York, Oregon, Texas, and Washington. The CDC partially attributed the outbreak to "US communities with pockets of unvaccinated people."

According to the CDC, the majority of the people who got measles were not vaccinated.

FDA Commissioner Dr. Scott Gottlieb recently told CNN in an interview that lax enforcement of vaccination requirements by some states could be to blame.

Anti-vaccine communities span the political spectrum, a phenomenon perhaps best illustrated by vaccine skeptic Robert F. Kennedy Jr.'s meeting with then President-Elect Donald Trump in 2017. Trump asked Kennedy to chair a commission on vaccine safety, Kennedy said afterward; the commission never came to fruition.

Offit said the measles outbreak is a sign that the anti-vaccine movement has real consequences.

"Do we have to wait until there's a few thousand cases of measles and children start to die. Will that move us?" he said. "Invariably it is the children who will suffer from our ignorance."