The public conversation over vaccines in America has been clouded by confusion, debunked scientific studies and unfounded claims over toxins and vaccine injury.
But one image that spread widely on Thursday told a clear story: the actress Jessica Biel, sitting next to Robert F. Kennedy Jr., who has publicly questioned the safety of vaccines, on a trip this week to lobby the California Legislature against a bill that would toughen immunization requirements in the state.
Ms. Biel’s lobbying efforts in Sacramento, and her association with Mr. Kennedy, who lauded her on Instagram as “courageous,” prompted a swift and furious response from those who criticized her for seeming to oppose vaccines.
Ms. Biel quickly issued a statement on Thursday insisting that she is supportive of vaccines.
But her backpedaling did little to quell the outrage from parents, doctors and others who have accused those in the anti-vaccine movement of allowing highly contagious diseases like measles to spread in the United States. With an outbreak of the measles underway and state legislatures around the country debating immunization requirements, the entry of another prominent celebrity into the debate both broadened the scope of the national discussion around the issue and provoked an unusually fierce pushback from the medical community.
“I think what’s happened is there is a more organized and engaged opposition to celebrity claptrap and nonsense, and in general anti-vaccine malarkey,” said Arthur L. Caplan, a bioethicist at the N.Y.U. School of Medicine. “Defenders of vaccination are much more engaged. They’re saying, we’re not going to put up with anti-vaxxers and celebrities maneuvering around the edges of the debate.”
Nationwide, 1,022 new cases of measles were reported in the United States as of June, the largest number of new cases since measles was declared eliminated in the United States 20 years ago.
Ms. Biel and Mr. Kennedy met with legislators at the California Statehouse, according to photos Mr. Kennedy posted to Instagram. Ms. Biel framed her lobbying against the bill as an effort to support parental rights, according to a statement she posted to Instagram on Thursday.
“I support children getting vaccinations and I also support families having the right to make educated medical decisions for their children alongside their physicians,” she wrote in the post.
[Read more on the California legislation.]
In campaigning publicly against the legislation, Ms. Biel follows a number of celebrities who have spoken out in recent years on the issues of vaccinations and parental rights. Jenny McCarthy, a former co-host of “The View,” has for years suggested that the measles-mumps-rubella vaccine caused her son’s autism. Robert De Niro, who has a son on the autism spectrum, promoted a documentary about the alleged dangers of vaccines. Other celebrities who have questioned the benefits of vaccines and medical exemptions limits include Alicia Silverstone, Jenna Elfman and President Trump.
Since Mr. Kennedy, 65, started raising questions about the safety of childhood vaccines, challenging a cornerstone of public health, he has become the most recognizable face in the vaccine wars. Scientists have denounced his ideas as dangerous, saying they will lead to epidemics that kill children. He has been abandoned by even stalwart supporters and has lost many friends.
Photos Mr. Kennedy posted to Instagram on Wednesday showed him and Ms. Biel with California lawmakers and activists, including Autumn Burke, a State Assembly member who opposes the bill and voted in 2015 against legislation that would have restricted vaccination exemptions.
On social media on Thursday, Ms. Biel’s stance on the California legislation prompted many enthusiastic responses from fans and parents who are suspicious of vaccines. But there were also withering comments from people like the actor Bradley Whitford, who wrote on Twitter that he had an uncle who died of whooping cough. “#pseudosciencekills,” he added. “Vaccinate your kids.”