Public figures, including HHS Secretary Kennedy Jr. and some politicians and social media accounts, shared the idea that childhood vaccines in the U.S. were never tested in long-term, placebo-controlled trials. Their posts and interviews helped the claim spread widely on platforms like Twitter and in news stories. This idea was mentioned in ACIP meetings, public hearings, and across social media in 2025, making it a common talking point among anti-vaccine groups and influencers.

A placebo is something used for comparison in a study. Many people think a placebo must always be saline (salt water), but that is not always true. An inert placebo (like saline) has no active ingredients.

An active control may contain something already known to be safe, like another vaccine or vaccine ingredients such as stabilizers or adjuvants (ingredients that help the vaccine work better). These added ingredients make sure that the person getting the vaccine or placebo cannot tell which one they actually received. If they could tell, it might change how they describe their symptoms to the scientists in charge of the trial

Both types are accepted in science, depending on the situation. And despite what some people claim, many childhood vaccines were tested using saline placebos, including vaccines for:

• Rubella vaccine
• Pneumococcal vaccine
• Hib vaccines
• HPV vaccine
• The Salk Polio vaccine
• Measles vaccine
• Tdap vaccine
• COVID vaccine

These trials looked at both safety (does it cause harm?) and effectiveness (does it prevent disease?).

The World Health Organization (WHO) gives guidance on when placebos should be used. Using a saline placebo is ethical when no effective vaccine already exists. But if a safe and effective vaccine is already available, it can be unethical to give some people an inert placebo. Doing so would leave them unprotected against a serious disease, even though we know they could get hurt.

A good example is the pneumococcal vaccine. Prevnar-13 was tested against Prevnar-7, an older vaccine that already worked. Using saline instead would have meant leaving children unprotected against dangerous bacterial infections. That would have put children at real risk of serious illness or death.

In these cases, scientists compare the new vaccine to an older one to make sure it works as well or better, while still keeping people safe.

Why not just use saline placebos? The answer is simple: babies are vulnerable. When scientists already know a vaccine prevents serious disease, they do not want to leave some babies unprotected just to satisfy a study design.

Instead, researchers:

• Compare new vaccines to trusted older ones
• Track safety through long-term studies
• Monitor millions of real-world doses after approval

Vaccines are tested for many years. For example, the hepatitis B vaccine was tested on thousands of people before it was given to newborns. Scientists looked carefully for both short-term and long-term side effects.

Some also claim that the hepatitis B vaccines were only tested for five days. They came up with this idea from reading vaccine package inserts, which are legal documents, not full research reports. The “five days” only referred to watching for mild problems at the injection site, like a sore leg. Serious health problems were tracked for months, and other symptoms like fever were tracked for weeks.

Hepatitis B can cause lifelong infection, liver damage, and liver cancer. The younger someone is when infected, the more likely it is to become chronic. There is no cure, but the vaccine can prevent it. That is why protecting infants early is so important.

Science does not rely on rumors or shortcuts. It relies on careful testing, ethical rules, and ongoing safety monitoring.

In 2025, the “sanitation, not vaccines” trope spread widely. It claims that clean water, nutrition, and hygiene — not vaccines — are what reduced deadly diseases. It spread because well-known public figures and podcasts talked about these ideas in simple ways that were easy to clip, share, and spread across social media like Twitter and YouTube.

Clean water, safe sewage systems, and good nutrition save millions of lives. They are especially important for diseases spread through food and water, like diarrhea, which still kills over 500,000 children under age five each year worldwide.

Sanitation helped make people less likely to die once they were sick. Better food, cleaner hospitals, and improved care meant stronger bodies and better recovery. But many dangerous diseases spread through the air, not through dirty water. For these diseases, sanitation does very little to stop infection.

This is where many charts are confusing. They often show death rates, not how many people actually got sick. Deaths went down over time because care improved, even while large numbers of people were still being infected. Before vaccines, nearly every child got measles, polio caused tens of thousands of cases each year in the U.S., and smallpox kept causing outbreaks around the world.

When vaccines were introduced, case numbers dropped sharply, not just deaths. Looking only at death charts hides this difference and makes it seem like vaccines were not needed, when they were actually the turning point.

Measles is one of the most contagious diseases ever known. It spreads through the air and can stay in a room for up to two hours after a sick person has left. If one person has measles, an unvaccinated person has a 90% chance of getting sick.

Before the measles vaccine in 1964:

• Nearly all children got measles by age 15
• 500–600 children died each year in the United States

Two doses of the MMR vaccine prevent about 98% of measles cases. Vaccination has prevented tens of millions of deaths worldwide. Good nutrition and vitamin A can help someone recover, but they do not stop measles from spreading.

Polio is caused by a virus, not chemicals like DDT. Scientists have isolated the poliovirus many times and shown that it causes paralysis.

Before vaccines:

• The U.S. had about 57,000 polio cases in 1952
• Over 21,000 of those cases caused paralysis

Polio spreads through tiny amounts of fecal matter (poop), often without anyone knowing. Before modern sanitation, most children were exposed to polio as babies, when they were protected by antibodies from their mothers. They usually had mild illness and became immune.

When sanitation improved in the early 1900s, children were exposed later in life, after that protection was gone. This led to larger and more severe outbreaks, even though overall health improved. Sanitation changed who got polio, but it did not stop the virus. Vaccination did.

We still vaccinate for polio today because the virus still exists in parts of the world and can return through travel, as shown by the U.S. polio case in 2022.

Smallpox spread through the air, not dirty water. Even as sanitation improved, smallpox continued to cause deadly outbreaks for centuries. Smallpox was eradicated through a global vaccination campaign. Since eradication in 1980, there have been zero natural cases anywhere in the world. No sanitation effort has ever achieved this for an airborne disease.

One of the most consistent rumors of the last five years is that COVID vaccination causes cancer.

After years of careful monitoring, there is still no evidence that COVID vaccines cause cancer. No studies show a rise in cancer linked to vaccination, and there is no realistic biological process that explains how vaccines could cause cancer. These claims rely on misunderstandings of biology, poor-quality data, or fear-based language rather than solid evidence.

One variation of this claim is something they call “turbo cancer.” These claims sound frightening, but they are not supported by science. When scientists carefully study how vaccines work and examine real-world data, they find no evidence that vaccines cause cancer or change a person’s DNA.

The idea of “turbo cancer” is not a real medical term. Doctors and scientists do not use it, and it does not describe any known disease. Cancer does not appear suddenly. Even the strongest cancer-causing substances, called carcinogens, usually take many years to cause cancer because damage builds up slowly in cells over time. If vaccines caused cancer, scientists would expect to see increases years later, not right after vaccination.

Researchers also study health patterns in very large groups of people. These studies look for real-world trends across millions of individuals. When scientists examine this data, they do not see an increase in cancer linked to COVID vaccines. Some people point to rising cancer rates in younger adults, but this trend began in the early 1990s, long before COVID vaccines existed.

Despite this, some critics claim vaccines contain dangerous DNA that can damage our genes. These claims often come from studies that have serious problems. In some cases, the researchers tested expired vaccines or vaccines that were not stored correctly. This matters because mRNA is fragile and breaks down quickly, especially with heat or time, while DNA is much more stable. When mRNA breaks apart, the tiny leftover DNA can look larger by comparison, even though the amount has not changed. This can make test results misleading.

The DNA being discussed is not harmful or active in the body. It comes from a promoter gene, which works like a light switch used during vaccine production to tell cells when to start making RNA. Promoter genes help manufacture the vaccine but are not meant to be ingredients. Almost all of this DNA is removed before the vaccine is finished, and any tiny traces left behind are not dangerous.

More importantly, vaccines cannot change your DNA. Vaccine mRNA stays in the cytoplasm, the outer area of the cell where proteins are made. Our DNA is kept safely inside the nucleus, which has a strong protective barrier. Vaccine material does not have the signal needed to enter the nucleus. Even if it could, it would still need a special helper protein, called an enzyme, to attach to DNA. One such enzyme, integrase, acts like glue. But the vaccines do not contain integrase, so they cannot get to your DNA.

There is also a basic biology reason these claims do not work. Human DNA is double-stranded, like a zipper with two matching sides, while mRNA is single-stranded, like a loose string. Because they are built differently, mRNA cannot merge with or rewrite DNA. This is why mRNA vaccines are not gene therapy. They give temporary instructions to make a protein and then break down and leave the body.

Science does not depend on one study or one voice. It works by testing ideas, repeating experiments, and having many experts review the results. When scientists around the world examine the same question and reach the same conclusion, this is called scientific consensus. The scientific consensus is clear: COVID vaccines do not cause cancer.