Some think there is a global conspiracy to promote harmful vaccines. But doctors and health experts agree: Vaccines are safe and they save lives.

Pediatricians, the World Health Organization, the U.S. Centers for Disease Control and Prevention, Europe’s Centers for Disease Control and other medical groups agree: Vaccines are safe and they save lives.

But the internet has fueled a growing, vocal movement of vaccine skeptics, who raise questions about vaccine safety and who often claim there’s a vast global conspiracy to promote harmful vaccines.

The claims have been repeatedly debunked, often at great expense.

And for the conspiracy claims to be true, they would have to include not only the large pharmaceutical companies but the entire leadership of the WHO, the CDC, the ECDC, independent academic researchers, virtually all of the medical doctors in the world and other public health leaders.

The conspiracy would have to have hoodwinked people who have completed advanced academic studies in immunology, public health and epidemiology, not to mention medical school graduates.

Below are some of the more common myths that make the circuits regularly.

Myth #1: Vaccines contain toxic substances

Many vaccine skeptics argue that vaccines are loaded with heavy metals, including mercury, as well as other poisons such as formaldehyde.

They say anyone with “common sense” could see that these are poisons no one would want to inject into the body of a small child. You’ll often see people posting comments that say the toxins are listed right on the package insert.

It is true that the ingredients of vaccines are listed on package inserts. The U.S. CDC has a website that lists them, as well. These ingredients have all been tested and have been found to be safe.

Formaldehyde, for example, is made naturally in the human body. As with any other chemical, the dose makes the poison, and there’s not enough in vaccines to cause harm.

The same goes for a mercury-based preservative called thimerosal. The mercury in thimerosal is chemically bound, meaning it cannot react to living tissue. It’s quickly cleared by the body without causing damage.

Thimerosal keeps dangerous bacteria and fungi from growing in vaccine vials. But because of fears about thimerosal, it’s been removed from all childhood vaccines made for the U.S. market and is less and less frequently found in vaccines sold in other countries, as well.

Vaccines also sometimes contain aluminum, but according to the American Academy of Allergy, Asthma and Immunology, vaccines that do contain aluminum deliver less than what the average person typically gets from food every day.

Myth #2: Vaccine makers are immune from lawsuits

Another common argument is that vaccine manufacturers are completely immune from lawsuits filed by the families of people injured by vaccines. Or they argue that thousands of people, often a high percentage of those vaccinated, are injured by vaccines.

It is true that in the United States, there’s a program called the Vaccine Injury Compensation Program, a federal “no-fault” system to compensate people who are injured by childhood vaccines. No medical intervention is 100% safe, and there are people who can suffer rare adverse reactions to vaccines.

Henry Waxman, a retired member of Congress who helped write the law setting up the program, says it was put into place because vaccine makers threatened to stop making vaccines because they were spending too much time and money fighting lawsuits.

Many of the lawsuits were unfounded, but companies still had to put up a defense. Public health officials feared that a cessation of production could lead to a shortage of vaccines.

The program is paid for by a tax on vaccines.

One valid vaccine injury for every one million vaccines given

The program uses a list of adverse events that have been scientifically demonstrated to have been caused by vaccines. One of these is Guillain-Barre syndrome, a rare nerve disease that can be caused by infections and sometimes by “live” vaccines.

Another is a severe allergic reaction, also known as anaphylaxis. People can faint after receiving vaccines, and fainting-related injuries are included on the list.

Autism is not one of the covered conditions.

In 2009, a special federal court called the U.S. Court of Federal Claims ruled against three families who claimed their children’s autism was caused by vaccines. The judges said in the ruling that the families had been misled by physicians guilty of “gross medical misjudgment.”

Between 2006 and 2017, 3.4 billion vaccine doses were given in the United States, according to the CDC. During the same period, 6,314 people applied to the program for compensation, and 4,328 of those claims were found to be valid. This works out to about one valid vaccine injury for every 1 million vaccines given.

Denmark, Germany, Britain, France, Switzerland and Japan also have national vaccine injury compensation programs.

Anyone can report side-effects from any drug or vaccine, but such reports cannot show that the drug or vaccine actually caused the injury. For example, a person could die of a heart attack after taking a certain drug. Did the drug cause the heart attack, or did something else? That must be investigated separately.

Myth #3: Vaccines cause autism

The persistent myth that vaccines cause autism comes from a study published by a disgraced former doctor named Andrew Wakefield. His medical license was withdrawn after he was found to have falsified data, but Wakefield is now a leader in the anti-vaccination movement.

The U.S. National Academy of Medicine has spent decades looking at this claim over and over again. It has issued several reports dating back to 2001 saying there is no evidence to show vaccines could cause autism. Subsequent reports said there is really no link between vaccines and autism, and that experts who want to find out what causes autism need to spend time and money looking elsewhere.

Studies have shown that there is no difference in the rates of autism between children who are vaccinated and those who are not. The latest study comes from Denmark and shows that vaccinated kids are no more likely to develop autism than unvaccinated children.

Myth #4: Vaccines cause sudden infant death syndrome

The U.S. National Academy of Medicine has also investigated the claim that vaccines cause sudden infant death syndrome. They have found it to be untrue.

Myth #5: Kids get too many vaccines, and too early

The global vaccine schedules are set based on when children are likely to be exposed to diseases and when their immune systems are mature enough to develop good responses to vaccines. Waiting to deliver vaccines just leaves children vulnerable to infections, doctors say.

Experts in immunology point out that newborn babies breathe in thousands of germs with their first cries. The amount of antigen in vaccines — that’s the piece of bacteria or virus put in to stimulate an immune response — is far less than the number of antigens people are regularly exposed to.

And because of better manufacturing techniques, the amount of vaccine antigen given is far lower than it was in previous years.

Combined vaccines like the MMR vaccine or the diphtheria-tetanus vaccine allow for several doses to be given in a single shot, saving money and time, and sparing the child the pain of yet another jab.

About one in six kids gets a fever after receiving the first dose of MMR vaccine. This risk rises as children get older, so doctors say it’s better to give this vaccine earlier.

Myth #6: Vaccines spread the diseases they are meant to prevent

Like many rumors, the myth that vaccines spread the diseases they are made to prevent is based on a little piece of truth.

There are two types of polio vaccine. One is made using a “live” virus, and the other, a shot, is made using inactivated virus. The live polio virus vaccine can sometimes change in a child’s body, and they can excrete infectious polio virus. It can be found in sewer systems and causes occasional outbreaks.

Because of this, the WHO recommends immunizing children first with an inactivated jab and then boosting with oral drops that contain live virus.

Measles vaccines use a live but weakened virus also. But studies have shown it doesn’t come back to full life in the body and it does not spread from person to person.

Because measles vaccine uses a live virus, people with weakened immune systems or people with tuberculosis should not get the vaccine. That’s why public health experts say it’s very important for fully healthy people to get the MMR vaccine: to protect themselves but also to protect others around them who cannot be vaccinated.

Maggie Fox has been reporting on health and science for more than 20 years and is currently a consulting editor to Medscape and WebMD and a consultant on health and science news. She has covered conflict, politics and other international events from London, Hong Kong and Beirut. She has covered the cloning of Dolly the sheep, Ebola epidemics, stem cell technology, vaccine controversies and other stories for Reuters, CNN, National Journal and NBC News. She lives in Washington, DC.