Washington CNN  — 

Three members of Robert F. Kennedy Jr.’s family are forcefully denouncing his anti-vaccine views, arguing that the lifelong Democrat “is part of a misinformation campaign that’s having heartbreaking — and deadly — consequences.”

Kennedy, the son of late presidential candidate Robert F. Kennedy, is one of the more notable anti-vaccine activists. He wrote a book in 2014 about mercury in vaccines and lobbied Congress to give parents exemptions from state requirements for vaccinating their children.

Wednesday’s Politico op-ed — written by former Maryland Lt. Gov. Kathleen Kennedy Townsend, former US Rep. Joseph P. Kennedy II and Maeve Kennedy McKean — pointed to the latest outbreak of measles in the United States and worldwide.

“Robert F. Kennedy Jr. — Joe and Kathleen’s brother and Maeve’s uncle — is part of this campaign to attack the institutions committed to reducing the tragedy of preventable infectious diseases,” the authors wrote.

Across the United States, 764 cases of measles have been reported since January 1, according to the latest numbers shared by the Centers for Disease Control and Prevention.

“These tragic numbers are caused by the growing fear and mistrust of vaccines — amplified by internet doomsayers,” the three members of Kennedy Jr.’s family wrote.

They argued that Kennedy Jr. “helped to spread dangerous misinformation over social media and is complicit in sowing distrust of the science behind vaccines.”

While affirming their love for Kennedy Jr., the three family members said he’s “wrong” on vaccines and his work against vaccines is “having heartbreaking consequences.”

“We are proud of the history of our family as advocates of public health and promoters of immunization campaigns to bring life-saving vaccines to the poorest and most remote corners of America and the world, where children are the least likely to receive their full course of vaccinations. On this issue, Bobby is an outlier in the Kennedy family,” they said.

Kennedy, who chairs the Children’s Health Defense, a nonprofit group that expresses skepticism about the health benefits of vaccines, insisted in a statement that he’s not “anti vaccines” — but stressed that he wants “safe vaccines with robust safety testing” and doesn’t believe “we should be forcing pharmaceutical products on unwilling American citizens without understanding the downside risks.”

“I love my family. The Kennedys have a long and continuing history of involvement with the public health agencies. It is very difficult for any of us to accept that any of those officials would be less than candid about vaccine risks,” Kennedy said.

According to the World Health Organization, vaccination “is one of the most cost-effective ways of avoiding disease” and prevents 2 million to 3 million deaths a year.

The organization included “vaccine hesitancy -— the reluctance or refusal to vaccinate despite the availability of vaccines” -— on its list of 10 big threats to global health in 2019.

This story has been updated.

CNN’s Dan Merica and Debra Goldschmidt contributed to this report.