geoff: More than 75 Nobel laureates this week signed a letter asking the U.S. Senate not to confirm health and human services secretary nominee Robert F Kennedy junior, citing his opposition to vaccines among their concerns.

As we delve deeper into a range of issues connected to the incoming trump administration, William brangham is back with another explaining, a look at Kennedy's record on vaccines and what impact he could have leavy - - leading the nation's health agencies.

>> Just as the vaccines stimulate production by the body, billions of antibodies which build a wall.

William: Vaccines are easily one of modern medicine's most successful interventions.

Over the past two centuries, virtually eradicating diseases like smallpox, polio, measles, and many others that once regularly disfigured, disabled, and killed hundreds of millions of people around the world, many of them children.

Dr. Michael osterholm directs the center for infectious disease research and policy at the university of Minnesota.

>> The bottom line is, for every two days we've lived in the last century, we've gained a day of life expectancy.

That's incredible.

And it's because of these tools, notably vaccines, that that's happened.

William: That's not to say there are no risks to them, including occasional allergic reactions, injuries and in rare cases, deaths.

And public health experts like osterholm say it is important to examine and continually monitor any adverse effects.

But on balance, those risks are far lower than those of the diseases they are protecting against.

>> Today if I were in an automobile accident and I had my seat belt on, but somehow the seatbelt jammed and I was unfortunately trapped in the car and the car caught on fire, this would be a horrible tragedy.

Would anybody say we got to eliminate seatbelts now?

No, because, in fact, there have been many, many, many more lives saved because of seatbelts as opposed to not.

William: Yet, over the past couple of decades, there has been a small but growing vocal minority pushing back against vaccines because of perceived harms, including the debunked claim that the measles, mumps and rubella vaccine causes autism.

That linkage was put forward in a late 1990's paper in the British medical journal the lancet.

It was later retracted and has since been repeatedly disproven.

The doctor behind that study, Andrew Wakefield, was stripped of his medical license.

But over that period, Robert F. Kennedy, Jr. Who trained as an environmental lawyer, has become a principal player in this movement, along with Wakefield.

>> He is a voice machine that continues to put out dis and misinformation in such a way that it sounds believable to the public.

William: In 2005, Kennedy wrote an article for rolling stone magazine and salon that asserted a connection between autism and a mercury-containing vaccine additive, thimerosal.

Thimerosal was removed from childhood vaccines in 2001, and it was never used in the mmr vaccine.

After that piece ran, the two publications discovered multiple errors in his work, and retracted it.

A decade later, Kennedy joined a group called the world Mercury project, which a few years later became children's health defense, which is a nonprofit that has been a principal promoter of misinformation about vaccines.

>> That's when it seems that he really got embedded in the anti-vax world and saw a lot of - - in the anti-vax world.

William: Derek Beres has long tracked Kennedy's influence for his podcast, conspirituality, which is about the intersection of the wellness industry and online conspiracies.

>> You have Robert Kennedy, you have del bigtree, you have a number of people who have been doing that work for a long time, but covid gave them the opportunity to have an even larger platform than they ever had.

William: Months before the covid pandemic began, Kennedy met with antivaccine advocates on the island nation of Samoa.

Which had seen a huge drop in its vaccine rates after a medical mistake killed two children.

In late 2019 there was a measles outbreak there.

83 people died, many of them young children.

Kennedy later called the outbreak mild and denied playing any role in it.

When covid-19 arrived to the U.S., many Americans became frustrated with the evolving and sometimes conflicting guidance on wearing masks and the protections provided by vaccines, as well as the many stay-at-home orders impacting schools, churches, and businesses across the nation.

That frustration became highly politicized, and donations surged to Kennedy's nonprofit, which went on to finance the documentary series called plandemic, which alleged a shadowy group was using the coronavirus and vaccines to get rich and powerful.

>> If we activate mandatory vaccines globally, I imagine these people stand to make hundreds of billions of dollars that own the vaccines.

>> I cannot think of anything more consequential for the anti-vax movement than plandemic.

It struck an emotional chord at a time when everyone was locked inside and really confused about their own lives and about existence in general.

And it's understandable that you would be confused by what's happening if you've never experienced it.

But that doesn't give people the right to spread misinformation to the level that plandemic did.

And I think we're going to be feeling the consequences of that propaganda film for generations.

William: Post-pandemic, Kennedy has continued to criticize the recommended vaccine schedule for children that is put out by the centers for disease control and prevention, as well as adult covid and flu vaccines.

>> Can you name any vaccines that you think are good?

>> I think some of the live virus vaccines are probably averting more problems than they are causing.

There is no vaccine that is, you know, safe and effective.

William: And yet Kennedy has often argued that he is not anti-vaccine but in favor of vaccine safety.

>> If vaccines are working for somebody, I'm not went to take them away.

People ought to have choice and ought to be informed by the best information.

So I'm going to make sure the scientific safety studies and efficacies are out there and people can make individual assessments.

>> Let's be really clear about the fact that he is anti-vaccine messenger.

And he has continued to be.

We have many examples of that.

The second thing is that in this country, and for that matter, throughout the world, when vaccines are licensed and approved, all the safety data that goes into licensing, that vaccine is made public.

There is nothing hidden in a vault somewhere or if it were just opened up, the public would now have sunshine on a vaccine issue they did not have before.

William: Ultimately, osterholm says elevating Kennedy to the head of health and human services could do a number of things to weaken vaccine policy and vaccine uptake in the country.

By lending a veneer of legitimacy to his many disproven claims, allowing him to influence the licensing of new vaccines, and by firing many of the public health experts at HHS.

>> As we have more and more infections occur as a result of fewer and fewer people being vaccinated within, you know, literally a few years, we could be back into a period not that dissimilar to what we had happening in the early 1900s before vaccines.

That's hard for people to imagine.

William: For the pbs news hour, I am William brangham.

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