The MMR vaccine doesn’t contain ‘aborted fetus debris’, as RFK Jr has claimed. Here’s the science

Robert F. Kennedy Jr, the United States’ top public health official, recently claimed some religious groups avoid the measles, mumps and rubella (MMR) vaccine because it contains “aborted fetus debris” and “DNA particles”.

The US is facing its worst measles outbreaks in years with nearly 900 cases across the country and active outbreaks in several states.

At the same time, Kennedy, secretary of the Department of Health and Human Services, continues to erode trust in vaccines.

So what can we make of his latest claims?

There’s no fetal debris in the MMR vaccine

Kennedy said “aborted fetus debris” in MMR vaccines is the reason many religious people refuse vaccination. He referred specifically to the Mennonites in Texas, a deeply religious community, who have been among the hardest hit by the current measles outbreaks.

Many vaccines work by using a small amount of an attenuated (weakened) form of a virus, or in the case of the MMR vaccine, attenuated forms of the viruses that cause measles, mumps and rubella. This gives the immune system a safe opportunity to learn how to recognise and respond to these viruses.

As a result, if a person is later exposed to the actual infection, their immune system can react swiftly and effectively, preventing serious illness.

Kennedy’s claim about fetal debris specifically refers to the rubella component of the MMR vaccine. The rubella virus is generally grown in a human cell line known as WI-38, which was originally derived from lung tissue of a single elective abortion in the 1960s. This cell line has been used for decades, and no new fetal tissue has been used since.

Certain vaccines for other diseases, such as chickenpox, hepatitis A and rabies, have also been made by growing the viruses in fetal cells.

These cells are used not because of their origin, but because they provide a stable, safe and reliable environment for growing the attenuated virus. They serve only as a growth medium for the virus and they are not part of the final product.

You might think of the cells as virus-producing factories. Once the virus is grown, it’s extracted and purified as part of a rigorous process to meet strict safety and quality standards. What remains in the final vaccine is the virus itself and stabilising agents, but not human cells, nor fetal tissue.

So claims about “fetal debris” in the vaccine are false.

It’s also worth noting the world’s major religions permit the use of vaccines developed from cells originally derived from fetal tissue when there are no alternative products available.

Are there fragments of DNA in the MMR vaccine?

Kennedy claimed the Mennonites’ reluctance to vaccinate stems from “religious objections” to what he described as “a lot of aborted fetus debris and DNA particles” in the MMR vaccine.

The latter claim, about the vaccine containing DNA particles, is technically true. Trace amounts of DNA fragments from the human cell lines used to produce the rubella component of the MMR vaccine may remain even after purification.

However, with this claim, there’s an implication these fragments pose a health risk. This is false.

Any DNA that may be present in this vaccine exists in extremely small amounts, is highly fragmented and degraded, and is biologically inert – that is, it cannot cause harm.

Even if, hypothetically, intact DNA were present in the vaccine (which it’s not), it would not have the capacity to cause harm. One common (but unfounded) concern is that foreign DNA could integrate with a person’s own DNA, and alter their genome.

Introducing DNA into human cells in a way that leads to integration is very difficult. Even when scientists are deliberately trying to do this, for example, in gene therapy, it requires precise tools, special viral delivery systems and controlled conditions.

It’s also important to remember our bodies are exposed to foreign DNA constantly, through food, bacteria and even our own microbiome. Our immune system routinely digests and disposes of this material without incorporating it into our genome.

This question has been extensively studied over decades. Multiple health authorities, including Australia’s Therapeutic Goods Administration, have addressed the misinformation regarding perceived harm from residual DNA in vaccines.

Ultimately, the idea that fragmented DNA in a vaccine could cause genetic harm is false.

The bottom line

Despite what Kennedy would have you believe, there’s no fetal debris in the MMR vaccine, and the trace amounts of DNA fragments that may remain pose no health risk.

What the evidence does show, however, is that vaccines like the MMR vaccine offer excellent protection against deadly and preventable diseases, and have saved millions of lives around the world.