Learn more about vaccines and vaccine safety.

Thanks to vaccination, diseases like smallpox, polio, diphtheria and yellow fever no longer pose a threat to many populations around the globe. Influenza vaccines, while not always able to prevent infection, often prevent illness and if you do get sick, your symptoms can be greatly reduced with the help of the Flu vaccine. Recently, scientists have developed a vaccine for HIV/AIDS that looks promising for preventing infection entirely.  

Vaccines are one of the greatest success stories in public health and are one of the most important health initiatives for reducing illness and death due to infectious disease.  

VACCINATION MYTH VS. FACT

Myth: Vaccines are unsafe.

Fact: Vaccines are incredibly safe. 

However, the possibility of side effects does exist as it does for any medication. Most side effects are mild, and the health risks associated with preventable diseases like measles far outweigh the low risk of a vaccine side effect. Most reactions, if they do occur, are the body doing the work needed to ensure the vaccine works. An immune response such as low grade fever, aches and fatigue means the vaccine is doing its job.  People often mistake this for a bad side effect ("I got the Flu vaccine and then I got the Flu!") and incorrectly assume this means the vaccine is not working or even caused the disease. 

The fact is, vaccines are one of the safest medications available, with billions of healthy people around the globe serving as examples.  Decades of research are the foundation for today’s vaccines, which go through clinical trials and a thorough evaluation by scientific and medical experts before they are approved. And, they are continuously monitored after they are approved for as long as they are on the market.  

Myth: Vaccines cause Autism, SIDS or other Diseases.

Fact: Vaccines do not cause Autism or SIDS. Vaccines CAN cause serious side effects, but this is extremely rare. 

This myth is primarily based on a single study of twelve children that has been debunked many times for it's lack of scientific rigor and for the lack of scientific credibility of the author. There has never been any reputable scientific evidence that vaccines cause autism. . 

Major side effects or harm from vaccines like Measles,  HPV, and Flu are incredibly rare and pose less of a risk than the diseases themselves. Like any medication, in very rare cases, a vaccine can cause a serious problem, such as a severe allergic reaction. But the safety of vaccines far outweighs any risk of adverse effects. Most side effects are mild, such as soreness at the vaccine site, body aches and low fever (as noted, indications the vaccine is doing its job). 

The benefits of vaccination greatly outweigh the risks, and without vaccines many more serious illnesses  and deaths would occur.

Myth: The ingredients in vaccines are dangerous.

Fact: Vaccine ingredients have been tested on billions of people and subjected to thousands of scientific studies. There is no evidence that the ingredients in vaccines are dangerous. 

There is a lot of confusion about vaccine ingredients. We hear words like "thimerosal", "mercury", and "aluminum" and might be concerned that these are being injected into our bodies. BUT, it's important to know:

1. Thimerosal is a chemical that contains ethylmercury, not methylmercury. This distinction is important because ethylmercury is quickly cleared from the body and bloodstream, whereas methylmercury (the type found in canned  tuna) can accumulate in the body. Thimerosal is a preservative and is only used in multi-dose vials of vaccine to ensure stability once opened. - BUT Thimerosal was removed  from most routinely recommended childhood vaccines in the United States by 2001. However, it is still used in some formulations of the inactivated influenza (flu) vaccine, primarily in multi-dose vials as noted (for example, where cold storage required for single dose vaccine is not available). Most people do not receive this type of vaccine and they are used in very rare occasions. This removal was initiated in 1999 as a precautionary measure, not due to evidence of harm caused by the low doses of thimerosal in vaccines.*  It's important to note:

• Measles, mumps, and rubella (MMR) vaccines do not and never did contain thimerosal.
• Varicella (chickenpox), inactivated polio (IPV), and pneumococcal conjugate vaccines have also never contained thimerosal.
• Thimerosal in vaccines has not been found to cause autism or other neurodevelopmental disorders, according to numerous scientific studies. 

2. Aluminum is added to some vaccines to help induce a stronger immune response. Aluminum is the third most common element on our planet, after oxygen and silicon. During the first 6 months of life, a breastfed infant will swallow more aluminum through their diet than they will take in via recommended vaccination.**

Myth: Vaccinations cause the diseases that they are meant to prevent.

Fact: Vaccines don't cause diseases, and here's why: They don't contain active germs.

Vaccines are also known as immunizations because they stimulate our immune systems to produce the antibodies needed to protect us from — or become immune to — diseases. The inactive viruses in vaccines essentially trick the immune system into thinking there's a threat so it will churn out those protective antibodies. The process of producing antibodies can sometimes cause a low fever or minor swelling, but not the actual diseases.

Fact: Myth: Vaccine-preventable diseases are just part of childhood. It is better to have the disease than become immune through vaccines.

Fact: Vaccine-preventable diseases have many serious complications that can be avoided through immunization. 

For example, more than 226,000 people are hospitalized from influenza complications including 20,000 children and about 36,000 people die from influenza each year. About 4 million deaths worldwide are prevented by childhood vaccinations each year. 

Myth:  Vaccinations aren't necessary when everyone around me is already vaccinated and immune (i.e. herd immunity).

Fact: Herd immunity can only be achieved with the help of vaccination. 

Herd immunity occurs when a large portion of a community is immunized against a contagious disease, reducing the chance of an outbreak. Infants, pregnant women and immunocompromised people who cannot receive vaccines depend on this type of protection. However, if enough people rely on herd immunity as the method of preventing infection from vaccine-preventable diseases, herd immunity will soon disappear.

Myth: Giving a child more than one vaccine at a time will overload their immune system. 

Fact: Scientific evidence shows that giving children several vaccines at the same time has no adverse effect on their immune systems.

Children are exposed to different substances that trigger immune responses every day.  A child is exposed to far more triggers from a common cold or sore throat than they are from vaccines. And simply eating food can introduce many new triggers into the body. 

On the other hand, there are actually many key advantages of getting several vaccines at once:

• fewer clinic visits;
• children are more likely to complete their recommended vaccinations on time;
• combined vaccination (e.g .DTaP or MMR) means fewer injections.

The immunization schedule is determined by decades of medical evidence showing there's an optimal window of time when vaccines are most effective in preventing — and children are most vulnerable to — these diseases. 

Many parents feel the CDC's previously recommended schedule is too aggressive. So they ask their pediatricians to deliver one vaccine at a time, and at a much slower pace. Beyond missing that window of effectiveness,  spacing out immunizations results in more office visits, more injections and, as a result, higher out-of-pocket expenses. The American Academy of Pediatrics suggests parents, in communication with their physician, follow this recommended schedule.

Myth: Vaccines contain microchips that can be used to track people.

Fact: Absolutely no vaccines  contain any microchips, including one that would let governments or any other entities in power track people.

This myth took hold during the Covid epidemic, but in order to be able to actually track people, a chip with 5G access (which is what these myths claim) would need to be about the size of a penny.  And, this chip would need to send signals through many layers of skin and subcutaneous fat, a technological process that does not exist. 

Myth: The effectiveness of vaccinations has never been proven.

Fact: Simply stated — and scientifically proven — vaccines are extremely effective.

Effectiveness of vaccines is carefully studied. Some vaccines have effectiveness upward of 95%. Countless scientific studies proving the effectiveness of vaccines can be found on websites like the American Academy of Pediatrics.

Myth: New federal guidelines for vaccines like Covid and MMR (Measles, Mumps, Rubella) and the childhood vaccine schedule mean I won't be able to access these vaccines or I will have to pay out of pocket.

Fact: It can be hard to keep up with the news about vaccine eligibility and insurance access.  But as of now, not much is changing for most MA residents.

Massachusetts has joined the Northeast Public Health Collaborative  (NPHC) to determine vaccination guidelines based on best practices and recommendations from leading physician professional organizations, including the American Academy of Pediatrics (AAP), the American College of Obstetricians and Gynecologists (ACOG), and the American Academy of Family Physicians (AAFP).

• 1/12/26-The CDC has revised the childhood vaccine schedule, removing recommendations for life-saving vaccines including RSV, Meningitis, Flu and Hepatitis A. These preventable diseases can be deadly. The American Academy of Pediatricians has recommended this vaccine schedule . As always, consult with your medical provider.
•  9/15/25 The NPHC has released guidelines for Covid. More vaccine recommendations are likely forthcoming.
• 10/8/25-The CDC has banned the combination MMRV (Measles, Mumps, Rubella and Varicella/Chicken Pox) vaccine. Most children do not receive this vaccine but moving forward these vaccines will be be delivered as two separate vaccines for everyone, one being the MMR and the other Varicella. 
• 10/8/25 Most insurers have committed to continue to cover vaccines, including MassHealth and the new CDC guidelines (10/8/25) continue to ensure coverage by private and public insurers, including Medicaid, Medicare, the Vaccines for Children Program and the Children's Health Insurance Program. However, you should check with your insurer for confirmation. 
• If you have questions or concerns about vaccines, talk to your health care provider

Myth: Vaccines aren't safe because the VAERS shows lots of bad outcomes from vaccines.

Fact: The VAERS (Vaccine Adverse Event Reporting System) is NOT a list of actual health outcomes from vaccines. VAERS is a publicly available, searchable database of reports that have not been verified by anyone.

The VAERS simply contains whatever people have voluntarily reported. There is no restriction on what people can report, as long as it happened at some point following a vaccination. This means events that happen even years later and have no obvious connection to a vaccine, such as a broken arm, end up reported in the system.  Many people incorrectly assume it’s things that are vetted and have causal relationships with the vaccine. Check out this article from Johns Hopkins for more information about VAERS and how it's actually used.

*CDC. Understanding how vaccines work. www.cdc.gov/vaccines/basics/explaining-howvaccines-work.html 2 Rubin L, Levin MJ, Ljungman P, et al. IDSA clinical practice guideline for vaccination of the immunocompromised host. Clinical Infectious Diseases 2014;58(3): e44–e100 https://academic.oup. com/cid/article/58/3/e44/336537

**Keith L, Jones DE, Chou CH. Aluminum toxicokinetics regarding infant diet and vaccinations.Vaccine 2002;20(3): S13-S17.www.sciencedirect.com/science/article/pii/S0264410X020016525FDA. Common ingredients in US licensedvaccines. www.fda.gov/vaccines-blood-biologics/safety-availability-biologics/common-ingredients-us-licensed-vaccines