Childhood vaccine ingredients are safe in the amount present in vaccines; cells, animal products, and viruses aren’t part of these ingredients

Vaccination helps people live longer and healthier by protecting them against life-threatening diseases that were widespread not long ago. According to estimates by the World Health Organization (WHO), immunization against preventable diseases saves between three and a half and five million lives every year.

Despite their remarkable success, misconceptions and myths about the safety of vaccine ingredients persist.

One example of this is an Instagram post published on 3 March 2024. The post listed several substances supposedly present in childhood vaccines, including aluminum, mercury, formaldehyde, monosodium glutamate, cells, serums, viruses and fetal DNA. The caption claimed that these substances are “toxins injected into healthy babies”.

The post received over 5,000 likes in one day. The Instagram account that published it, faithful_free_momma, regularly broadcasts vaccine misinformation to its almost 60,000 followers. Fact-checking organization Lead Stories and the Annenberg Public Policy Center documented earlier instances of unsupported and misleading claims about vaccines posted on this account.

The claim that vaccines contain harmful ingredients is a baseless myth. All vaccine components are safe in the amounts present in vaccines, as Health Feedback explained on multiple occasions. Below, we discuss each substance listed in the post in detail.

Mercury

Thimerosal (also known as thiomersal) is a mercury-containing compound that has been used as a preservative in some vaccines. This compound keeps the vaccine safe by preventing the growth of bacteria and fungi that could otherwise contaminate the vial when opened.

While thimerosal does contain mercury, this element can exist in different chemical forms. Elemental (metallic) mercury is naturally present in the environment, and its toxicity is mainly associated with chronic exposure and vapor inhalation.

Certain bacteria can transform elemental mercury into methylmercury. This compound is a potent neurotoxin that sometimes accumulates in fish and shellfish. Exposure to methylmercury can damage the nervous system and the kidneys and cause developmental problems during pregnancy.

However, vaccines don’t contain either of these forms of mercury. Instead, they contain ethylmercury. This compound is chemically different from methylmercury and is broken down and eliminated by the body much more rapidly. Therefore, ethylmercury is less likely to accumulate and be toxic than methylmercury.

The WHO and the European Medicines Agency both stated that no evidence suggests that the low amounts of thimerosal present in vaccines cause harm. Nevertheless, many countries including Europe, the U.S., and the U.K., removed thimerosal from childhood routine vaccines in the early 2000s.

Aluminum

Similar to mercury, vaccines also don’t contain aluminum in its elemental form but as aluminum salts. These salts act as adjuvants, which means they help boost the immune response to enhance the vaccine’s protection against disease. Thus, adjuvants help reduce the quantity of vaccine and the number of doses needed to develop immunity.

While exposure to high levels of aluminum is toxic, the amounts of aluminum that some (not all) vaccines contain are low and within the limits considered safe by regulatory agencies. No evidence suggests that these tiny amounts of aluminum salts are unsafe, even for babies, as Health Feedback explained in an earlier review.

It is important to keep in mind that aluminum is an abundant, naturally occurring metal that also has multiple industrial applications. The amount of aluminum in vaccines is much lower than the amount that an average person is exposed to daily through food, air, water, and soil.

For example, the Vaccine Education Center of the Children’s Hospital of Philadelphia explains that the amount of aluminum a child receives from vaccines is similar to the amount the child ingests in one liter of instant formula.

Monosodium glutamate

Monosodium L-glutamate (MSG) is the sodium salt of L-glutamic acid, a common amino acid that forms proteins in the body.

MSG is present in some vaccines as a stabilizer that protects them from damage caused by heat, light, or humidity during storage. This use is considered safe, and the amounts of MSG present in vaccines are minimal in comparison to other forms of exposure, such as through our diet.

Claims questioning the safety of MSG date back to the 1970s, after some people who had consumed foods containing MSG as a food additive reported symptoms such as headache, nausea, and sweating.

However, later scientific studies have shown no evidence of a direct link between MSG and these symptoms. A 2023 article in the blog Skeptical Raptor thoroughly discusses the scientific evidence on MSG safety and the possible origin of the myth.

The U.S. Food and Drug Administration classifies MSG as a food additive that is “generally recognized as safe” (GRAS). MSG is also approved as a food additive (E621) in the European Union.

Formaldehyde

Formaldehyde is a chemical commonly found in building materials, household products, and pesticides. It is also used as a fungicide, germicide, and disinfectant. Exposure to high levels of this chemical causes acute toxicity and increases the risk of developing some types of cancer.

Formaldehyde is used early in the vaccine manufacturing process to kill viruses or inactivate toxins that would make the vaccine unsafe. However, this chemical is removed later and isn’t present in the vaccine except in trace amounts.

In fact, the quantities of residual formaldehyde in vaccines are much smaller than those produced naturally in the human body. Therefore, there is no plausible mechanism by which they could cause harm, as Neal Halsey, professor emeritus at Johns Hopkins Bloomberg School of Public Health, explained to Health Feedback in 2019:

“Some vaccines do contain very small (trace) amounts of formaldehyde, which is a natural product produced by all mammalian cells. The trace amounts in some vaccines are residuals from the manufacturing process. In high concentrations, formaldehyde is toxic to cells and organisms. It is used to kill some of the organisms that are used to make vaccines and then purification removes all but a trace of the formaldehyde. The trace amounts that are left as a residual in vaccines are considered to have no additive effect to the naturally produced formaldehyde in our bodies.”

Aborted fetal DNA fragments, monkey kidney cells, and fetal bovine serum

The claim that substances such as cells and serum are injected during vaccination is inaccurate in several ways, as Health Feedback and others previously explained. First, these substances are simply not components of any approved vaccine. Second, the claim misrepresents materials used during vaccine production and conflates them with the actual components of the vaccines.

There are different types of vaccines, and some contain weakened or killed viruses. Because viruses can only replicate inside living cells, manufacturers grow them using different cell strains. They also use animal products like fetal calf serum to provide the cells nutrients they need to grow.

Once the vaccine viruses are ready, the manufacturers purify them to remove any cells, pieces of DNA, serum, and other substances used to help the cells grow. Therefore, these materials aren’t components of the final vaccine product.

It is also important to note that while some cell strains used during manufacturing are derived from human fetal and monkey cells, they differ from the original cells, which were collected decades ago. The strains now cultured in the laboratory never formed part of the tissue from which the original cells were collected. Hence, contrary to widespread claims, these cell strains can’t be considered tissue from monkeys or aborted fetuses.

Pig circoviruses

Regulatory agencies carefully oversee the manufacturing process to ensure the manufacturer’s facilities meet the required quality standards to produce the vaccines safely and consistently. This supervision also involves regular inspections of the vaccine manufacturing sites to ensure they comply with regulations.

Despite these strict regulations, rare cases of vaccine contamination might occur. One example is the pig circovirus to which the post referred.

In 2010, a research team found pieces of DNA from the porcine circoviruses PCV-1 and PCV-2 in the rotavirus vaccines from Merck and GlaxoSmithKline. These fragments weren’t part of the vaccine, but the result of contamination of an enzyme from the pig pancreas used in the manufacturing process.

Circovirus infections are common in pigs and are associated with several diseases in these animals. However, circoviruses aren’t known to cause illness in other animals or in humans.

But more importantly, the vaccines contained only fragments of the virus DNA, not the full virus. This is a key detail because, for replicating itself and causing infection, the virus needs to be intact and have all its components, not just parts of them.

Based on these facts and contrary to what the post implied, the presence of fragments of these pig viruses doesn’t pose a health risk to humans. Accordingly, regulatory agencies found no reason for concern.

In contrast, rotavirus infection causes severe diarrhea that is especially dangerous for infants and young children. For this reason, the WHO said that the risks from rotavirus infection outweighed any potential risks from PCV and didn’t recommend any change in the use of these vaccines.