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Vaccine Safety

Dr. Erez Gerty, Head of Impact at the Public Health Surveillance and Data Center, Ministry of Health
5 June 2025

Vaccines protect against serious and even life-threatening diseases, but unfounded rumors can discourage parents from vaccinating their children. We will examine some of these rumors, and provide tools for assessing the reliability of other rumors.

How a vaccine is tested: Each vaccine is tested in a series of clinical trials in humans in 3 stages:

  • On a small group of healthy people.
  • On a larger group of people.
  • On a huge group of people, with a control group that receives a dummy vaccine (placebo) or another known vaccine.

The substances vaccines are made of: In addition to the active substance, every vaccine contains additional substances that have a role. Their dosage in the vaccine is such that it should not harm those who receive the vaccine, and there are many studies that prove their safety at these doses.
Rumors versus reality: Many studies conducted in different countries have proven that there is no link between vaccines and autism, diabetes, SIDS, or allergies.
Monitoring side effects: In different countries, there are monitoring mechanisms whose role is to identify unusual and rare side effects even after the vaccine has been marketed. The best-known initiative is the American VAERS system, managed by the CDC and the FDA, which is based on self-reporting.
Choosing reliable sources of information: It is important to find out who is behind various publications in order to know if they are reliable. It is worth comparing any rumor about vaccines and their safety with reliable information based on scientific studies on the websites of the main health bodies in Israel and around the world. You can also consult your pediatrician with any questions and get the information directly from them.

Vaccines are one of the most effective and safest ways to prevent infectious diseases at ages when children are particularly susceptible. The protection of vaccines continues to accompany children for years to come, sometimes even for life. Vaccinations are sometimes accompanied by side effects, which usually stem from the activation of the immune system. Many rumors have been associated with these side effects and vaccines in general, which sometimes discourage parents from vaccinating their children.
We will examine some of these rumors, and provide tools for assessing the reliability of other rumors. But before that, how do you even test the safety of a vaccine?

The long road to obtaining vaccine approval

Each vaccine – from the oldest to the newest vaccines – is tested in a series of clinical trials in humans. Clinical trials are conducted in 3 stages:

Small group

The safety of the vaccine is tested on a small group of healthy people, from whatever age group it is intended 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 huge group of people, which can reach tens of thousands. At this stage, a control group receives a dummy vaccine (placebo), or another vaccine whose properties are known, with neither the researcher nor the person participating in the study knowing who received what – a blind test.

In each of the trials, reports are collected from each participant to identify possible side effects. At the end of the 3 stages, there is enough data, collected over a long period of time, so that the safety of the vaccine can be assessed and the possible side effects can be mapped.
At this stage, if the vaccine is safe and effective, it is approved and marketed, but its testing process does not end there. For 5 years, monitoring is conducted to identify extremely rare side effects, and there are precedents for vaccines in which new side effects were identified at this stage and were shelved. The older the vaccine is, and given to more people around the world, the risk of a new and rare side effect appearing is decreasing.

It is important to remember

It is important to remember

The routine vaccines customary in Israel are very old vaccines, which have been given for many decades around the world. The chance that something new and rare that has not been recognized will be discovered in them is slim. On the other hand, the risk from the diseases is clear and present.

The substances vaccines are made of

In addition to the active substance, every vaccine contains additional substances that have a role. Many parents are concerned about the rumors about these substances, but their dosage in the vaccine is such that it should not harm the body.
Here are some examples of substances that have been the subject of rumors:

A compound that contains the element mercury, which is used as a preservative to prevent contamination of the compound. This substance is important when using one vial to vaccinate several people. Due to the transition to individual doses, thimerosal is no longer needed, and it has been removed from most vaccines, including all routine vaccines used in Israel. Even when it was included in the vaccine, it was in a small and safe amount, as evidenced by quite a few studies.

This substance is added to inactivated vaccines. The purpose of aluminum salt is to stimulate the immune system and optimize its response, thereby improving the effectiveness of the vaccine. It is a safe substance that has been approved for consumption in the dose given in vaccines, and there is quite a bit of medical literature on this. Here is one study for example.

Found in tiny amounts in some vaccines and is used for fixation of viruses or toxins. This makes them harmless and preserves the structure of the virus so that the immune system can study it. What remains in the vaccine is only a tiny residue that cannot harm the body. In fact, the body produces formaldehyde naturally, as part of metabolic processes, at much higher levels than in vaccines, without harm, and it also knows how to break down this substance.

Used to maintain the integrity of the active ingredients during production, storage, and transportation. Sometimes there are claims about the toxicity of these substances, but their doses in vaccines are minimal and used once. In fact, the permissible and safe dose for consumption is several orders of magnitude higher than their dose in vaccines.

There are other substances, some real and some invented, about which rumors have been spread. In the end, every time a rumor is created about a new substance added to the vaccine, with which they try to arouse concern. Remember that all vaccines given in Israel have been thoroughly tested by doctors, by researchers in a long series of studies and through monitored reviews over time even after the vaccine has already been approved. The likelihood of surprises in an old vaccine is zero.
For detailed information on the substances commonly used in vaccines, you can delve deeper into the website of the U.S. Food and Drug Administration (FDA).
From here, we will move on to specific rumors about vaccines, and see how they do not stand the test of reality.

Vaccine safety: Rumors versus reality

  • 1
    There is no connection between the measles vaccine and autism Let's start from the end

    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.

Monitoring side effects


As mentioned, each vaccine has a large collection of studies that test them – from clinical trials to follow-up studies, including large studies that examined various phenomena in vaccinated versus unvaccinated individuals. These studies examined specific medical conditions or a list of medical conditions, and all of them show that vaccines are safe.
In addition to all these studies, there are government initiatives around the world that allow independent reporting of phenomena that occur shortly following vaccinations. These are monitoring mechanisms whose role is to identify unusual and rare side effects and report them. The best-known initiative is the American VAERS system, managed by the CDC and the FDA, which is based on self-reporting. The purpose of the system is to "raise a red flag" to healthcare systems in the event that independent evidence of a side effect accumulates around a particular vaccine, and it has proven itself in the past to be effective for these purposes. Thus, for example, the RotaShield vaccine against rotavirus was administered in the United States in 1998, and after evidence of side effects was collected in the VAERS system, the administration of the vaccine was discontinued in 1999.
It is important to remember that not every phenomenon that occurs after vaccination is related to the vaccine. If such phenomena are repeated in many people at a similar time after receiving the vaccine, this is the basis for conducting research to examine the connection between the phenomenon and the vaccine.
Regarding routine vaccines, as mentioned, these are very old vaccines, which have been given for many decades around the world. The chance that something new and rare that has not been recognized will be discovered about them is slim. On the other hand, the risk from the diseases is clear and present.

Choosing reliable sources of information online

The internet contains a tremendous abundance of information, not all of which is based and accurate, and it is important to find out who is behind various publications in order to know whether they are reliable. It is worth comparing any rumors about vaccines and their safety with reliable information based on research on the websites of the main health bodies in Israel and around the world:
Ministry of Health
U.S. Food and Drug Administration (FDA)
Centers for Disease Control and Prevention (CDC)
World Health Organization (WHO)

Websites in Hebrew with accessible information about vaccines:
Midaat (hebrew)
Vaccines (hebrew)
Parenting and Parents

You can also consult your pediatrician with any questions and get the information directly from them.
Finally, it is important to remember that the vaccine mimics the body's natural response to a pathogen, and that the entire event usually ends within two weeks of the vaccination. Events that occur months and years after receiving a vaccine are probably not related to it, while the damage caused by pathogens can be severe, and sometimes irreversible, and remain with us or our children for many years.

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