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Vaccine Safety

Vaccines
Safety
Dr. Erez Gerty, Head of Impact at the Public Health Surveillance and Data Center, Ministry of Health
5 February 2026

Vaccines protect against serious and potentially life-threatening diseases, but unfounded rumors can discourage parents from vaccinating their children. We will look at some of these rumors and provide tools to help assess the reliability of other claims.

How a vaccine is tested: Each vaccine goes through a series of clinical trials in three stages:

  • In a small group of healthy participants.

  • In a larger group of participants.

  • In a large group, including a control group that receives either a placebo (dummy vaccine) or another known vaccine.

The components of vaccines: Besides the active ingredient, every vaccine contains other substances that serve specific purposes. Their amounts are carefully measured to ensure they do not harm those who receive the vaccine, and many studies have shown they are safe at these levels.

Rumors versus reality: Many studies conducted in various countries have shown that there is no link between vaccines and autism, diabetes, Sudden Infant Death Syndrome (SIDS), or allergies.

Monitoring side effects: Different countries have set up monitoring systems to identify unusual and rare side effects even after a vaccine has been approved for use. A well-known initiative is the American Vaccine Adverse Event Reporting System (VAERS), managed by the CDC and the FDA, which relies on self-reporting.

Choosing reliable sources of information: It is important to check the sources behind various publications to determine their reliability. It is advisable to compare any rumor about vaccines and their safety with credible information based on scientific studies from leading health organizations in Israel and around the world. You can also ask your pediatrician any questions to get information from a trusted source.

Vaccines are one of the best and safest ways to prevent infectious diseases, especially when children are most at risk. The protection from vaccines usually lasts for years and can sometimes last a lifetime. While vaccines can occasionally cause side effects—usually because the immune system is reacting—many rumors have spread about these side effects and vaccines overall, which might make parents hesitant to vaccinate their children.

We will look at some of these rumors and give you tips on how to judge the reliability of other claims. But first, how is vaccine safety tested?

The lengthy process of getting vaccine approval

Each vaccine, whether old or new, goes through a series of clinical trials with people. These trials are done in three stages:

Small group

The vaccine's safety is tested on a small group of healthy people from the age group it is meant for, including infants.

Large group

The effectiveness of the vaccine is tested on a larger group of people.

Control group

The vaccine is given to a large group of people, often tens of thousands. At this point, a control group gets a placebo or another vaccine with known effects. Neither the researcher nor the participant knows who got which treatment, keeping the test blind.

In each trial, reports are collected from participants to identify potential side effects. By the end of the three stages, enough data has been gathered over a long period to evaluate the vaccine's safety and identify any possible side effects.

If the vaccine is found to be safe and effective at this stage, it is approved and marketed; however, the testing process doesn't stop there. For five years, ongoing monitoring takes place to identify very rare side effects. There have been cases where new side effects were found during this time, which led to the withdrawal of certain vaccines. As a vaccine is used more widely and ages, the chances of new and rare side effects appearing decrease.

Keep in mind

Keep in mind

The routine vaccines commonly used in Israel are well-known and have been given around the world for many years. The chance of finding something new and rare that hasn't been identified in these vaccines is low. On the other hand, the risks from the diseases they prevent are obvious and serious.

The Components of Vaccines

Besides the active ingredient, every vaccine has other substances that serve specific purposes. Many parents worry about rumors about these substances, but their amounts in vaccines are too low to harm the body.
Here are some examples of substances that have been talked about in these rumors:

A compound that contains mercury, which is used as a preservative to keep the compound from getting contaminated. This substance was important for using one vial to vaccinate multiple people. Since the shift to individual doses, thimerosal is no longer necessary and has been removed from most vaccines, including all routine vaccines in Israel. Even when it was included, it was in a small and safe amount, as shown by several studies.

This substance is added to inactivated vaccines. The purpose of aluminum salts is to stimulate the immune system and enhance its response, thereby improving the vaccine’s effectiveness. It is a safe substance that has been approved for use in the dosage given in vaccines, and there is substantial medical studies supporting its safety. For example, in a large national study from Denmark, researchers analyzed vaccination and medical records of over 1.2 million children over a 24-year period and found no evidence that exposure to aluminum in vaccines led to a statistically significant increase in the risk of developing a wide range of childhood-diagnosed conditions, including asthma and autism.

Formaldehyde is found in small amounts in some vaccines. It is used to make viruses or toxins harmless while keeping their structure for immune system research. The amount left in the vaccine is very tiny and cannot harm the body. In fact, the body produces formaldehyde naturally during metabolism at levels much higher than those in vaccines, and it does so without any harm. The body also knows how to break down this substance efficiently.

These substances are used to keep the active ingredients stable during production, storage, and transport. While there are claims about their toxicity, the amounts found in vaccines are very small and given only once. In fact, the safe amount for consumption is much higher than what is used in vaccines.

There are many substances, both real and fictional, that have been the subject of rumors. Whenever a new substance is rumored to be included in the vaccine, it tends to cause concern. However, it's important to remember that all vaccines given in Israel have been thoroughly tested by doctors and researchers through extensive studies and ongoing reviews, even after they are approved. The chance of unexpected problems from an established vaccine is very low.

For detailed information on the substances commonly used in vaccines, you can visit the U.S. Food and Drug Administration (FDA) website.

Next, we will look at specific rumors about vaccines and show how they do not match reality.

Vaccine safety: Rumors versus reality

  • 1
    There is no connection between the measles vaccine and autism

    Let's start from the bottom line. There is no connection between the measles vaccine and autism. The origin of this rumor is a study published in the late 1990s that suggested a link between the measles, mumps, and rubella vaccine (MMR) and intestinal infections in children diagnosed with autism. From there, it evolved into a rumor that the vaccine supposedly causes autism—a rumor that frightened many parents and caused them not to vaccinate their children. The results of this rumor and similar rumors are still seen today in repeated outbreaks of measles—one of the most contagious diseases known to man, with a significant rate of complications, including brain damage. It is important to understand: The vaccine does not cause autism, but the disease can cause brain damage.
    The study that started it all has since been refuted, and methodological and ethical problems have been discovered in it. Ultimately, a decade too late, the article was completely removed from the scientific literature. After the article was published, a series of studies were conducted on more than a million children worldwide. The most famous study is the "Danish Study", which examined data on all children born in Denmark between 1991 and 1998 (more than half a million children). About 80% of them received the MMR vaccine, and no difference in the rate of autism was seen between them and those who did not receive the vaccine. Even in a meta-analysis (combining data from several independent studies that examined a similar research question, thus reaching a more comprehensive and precise conclusion) that examined different studies, the findings indicated that there is no connection between the vaccine and the development of autism or autism spectrum disorder.
    There are many other studies, including one funded by anti-vaccination activists, which all reached the same conclusion. The connection between the vaccine and autism has been disproven time and time again, but a stone thrown by one fool into a well, even a thousand wise men will not be able to remove.

  • 2
    There is no connection between vaccines and the development of diabetes

    Type 1 diabetes, or juvenile diabetes, is an autoimmune disease (i.e. a disease in which the body produces destructive antibodies against itself), which results from the destruction of insulin-secreting pancreatic cells by the immune system. Many studies have examined whether there is a connection between various vaccines and juvenile diabetes, and their results indicated that there is no such connection. For example, a study conducted in Denmark examined children born in the country in 1990-2000 and demonstrated that there is no connection between type 1 diabetes and the vaccines they received. Another study examined the connection between receiving various vaccines in childhood and the age at which they were given and the risk of developing type 1 diabetes, and concluded that there is no connection between them. A meta-analysis conducted on many studies on the subject also found no connection between diabetes and vaccines.

  • 3
    Vaccines do not increase the risk of SIDS

    Many studies that have examined whether there is a link between receiving vaccines and the risk of SIDS (Sudden Infant Death Syndrome) have found that there is no pattern linking the two. For example, a British study examined SIDS deaths from 1993 to 1996 in five areas of Britain, with a total population of 17,000,000 people, but found no link between vaccines and SIDS.

  • 4
    Vaccines do not cause allergies

    In recent decades, there has been an increase in the incidence of allergies and autoimmune diseases. Since the rate of vaccinations also increased during this period, some people thought that there was a link between the two and believed that vaccines were the source of this. Many studies have examined the relationship between vaccines and allergies and autoimmune diseases over the years, but have found no evidence linking them. For example, this study. In contrast, other studies have indicated that the increase in allergies and autoimmune diseases is related to environmental changes such as air pollution and lifestyle changes.

  • 5
    The combination of vaccines in Israel is effective and safe

    Each of the vaccines given in Israel has been tested on the relevant age groups, and studies have also examined different combinations of vaccines – and they have been found to be safe and effective. In addition, the vaccines have been given to many millions of children in Israel and around the world in recent decades, and the medical information that has been accumulated on them is extensive and proves that they are indeed safe and effective.

  • 6
    Infant vaccinations are timed to support immune system development

    During the first months of life, babies receive multiple vaccines at HMO clinics, sometimes even at the same visit, because young infants are particularly vulnerable to various diseases. Vaccines help strengthen the baby’s immune system—like exercising a muscle—so it can defend against these diseases without putting strain on the body, unlike the diseases themselves.

Monitoring Side Effects

As noted, each vaccine has a large body of research behind it, from clinical trials through post-marketing follow-up studies. This includes large studies that compared vaccinated and unvaccinated people and examined a range of outcomes. These studies looked at specific medical conditions or lists of conditions, and all of them show that vaccines are safe.

In addition to all of these studies, there are government initiatives around the world that allow people to self-report events that occur shortly after vaccination. These are monitoring systems designed to detect unusual and rare side effects and bring them to attention. The best-known initiative is the U.S. VAERS system, run by the CDC and the FDA, which is based on self-reporting. The purpose of the system is to “raise a red flag” for health systems when independent reports of a possible side effect related to a specific vaccine begin to accumulate, and it has proven effective for this purpose in the past. For example, the RotaShield rotavirus vaccine was introduced in the United States in 1998. After reports of side effects were collected in the VAERS system, use of the vaccine was discontinued in 1999.

Choosing Reliable Online Information Sources

The internet contains an enormous amount of information, not all of it evidence-based or accurate. It is important to check who is behind different publications to determine whether the source is trustworthy. Any rumor about vaccines and their safety should be cross-checked against reliable, research-based information on the websites of leading health authorities in Israel and worldwide:

Hebrew-language websites with accessible information about vaccines:

If you have any questions, you can also consult your child’s pediatrician and get information directly from them.

Finally, it is important to remember that a vaccine mimics the body’s natural response to a disease-causing agent, and the entire process usually resolves within two weeks of vaccination. Problems that show up months or years after a vaccine is given are unlikely to be related to it. In contrast, the harm caused by infectious agents can be severe, sometimes irreversible, and may affect us or our children for many years.

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