1. What kind of side effects​ should I know about? 
Medicines sometimes cause reactions. The most common possib​le side effects from vaccines​ are fever or a  tender, red or swollen vaccination site. Serious allergic reactions are very rare​, happening about once in a million vaccine doses. If you are concerned about possible side effects, ask questions about what to expect. If you notice an unusual reaction hours or days after your child’s immunizations, call the doctor’s office for advice. 

2. Why do children today get so many immunizations? 
Thirty-five years ago, vaccines protected young children from only seven diseases. Today, we can protect them from at least 15 dangerous diseases because of medical advances. Many vaccines also require more than one dose to give children the best protection possible. 

3. How safe are vaccines? 
The American Academy of Pediatrics, the National Academy of Medicine, and the World Health Organization agree that vaccines are very safe​, and much safer than getting sick with the diseases that vaccines protect against. Millions of children and adults are vaccinated every year—safely. Thousands of people take part in rigorous clinical trials to test and develop safe and effective vaccines​ before the vaccines are licensed by the Food and Drug Administration (FDA). After being licensed, the Vaccine Adverse Events Reporting System (VAERS) helps track any health effects that may happen hours, days, weeks, or even months later. Anyone can report a possible side effect so that it can be studied. VAERS and other monitoring programs help ensure that vaccines are safe. 

4. Are diseases of the “old days” still around? 

Yes. Pertussis (whooping cough) is still common in the U.S. Other diseases, such as measles​ and polio​, are circulating in other parts of the world. It just takes one unimmunized traveler to bring an infectious disease home from another country. If immunization levels drop, the rare cases we have in the U.S. could very quickly multiply—putting our children in danger. 

• ​Measles. Measles remains common in many countries. Both children and adults can catch measles while traveling and spread it to others when they come home, often causing measles cases and outbreaks. 
  
• ​A pertussis report found that in 2024 (PDF), over 2,700 people in California became ill with whooping cough and one baby died. 
• Before chickenpox vaccine was developed, the disease put more than 10,000 Americans in the hospital and caused more than 100 deaths each year. Children who get chickenpox can get serious skin infections or pneumonia. 

5. What about holistic medicine? 
Holistic medicines may be helpful for some conditions, but only vaccines provide specific immunity to diseases. Only vaccines have been scientifically proven to protect against COVID-19, flu, whooping cough, measles, and other diseases. Holistic practitioners including the Naturopathic Doctors for Immunization​, and Dr. Andrew Weil​ from the Center for Integrative Medicine all support immunization. 

6. What about breastfeeding to keep babies healthy? 
Breastfeeding is very healthy for your baby, but breastfeeding alone cannot fully protect babies from diseases like whooping cough or measles. Although getting vaccinated during pregnancy can protect the youngest babies from some infections like pertussis and COVID-19, antibodies passed on from moms to babies during pregnancy only last for a few months. 

7. Why do kids need COVID-19 vaccines? 
COVID-19 has killed more than 1 million Americans and millions more around the world. Doctors have identified a very serious complication called Multisystem Inflammatory Syndrome in Children (MIS-C) that can be life-threatening. COVID-19 vaccines have been shown to protect children against MIS-C and other severe outcomes of COVID-19. Over 31 million children have safely received the COVID-19 vaccine in the United States, and ongoing safety monitoring shows that COVID-19 vaccinat​ion continues to be safe for children. Staying up to date with COVID-19 vaccines provides the best protection for children against severe COVID-19. 

8. What about “natural immunity”? 
Some people think getting a disease is the “natural” way to trigger the body’s immune response, but this comes at a risk—many vaccine-preventable diseases can have dangerous complications, like pneumonia, blindness, brain damage, and even death. 

Vaccines safely trigger a natural immune response—but do not cause the disease. While vaccines can prevent mild and severe illnesses, some, such as flu and COVID-19 vaccines, are more effective in preventing hospitalization and death than milder disease. 

9. Is it safe for a child’s immune system to have multiple vaccines? 
Yes. Children are exposed to hundreds of viruses and bacteria​​ ​during normal activities like eating and playing. Getting vaccines is no extra burden on the immune system—even for babies. Getting combination vaccines, like MMR (that protects against measles, mumps, and rubella), or getting multiple vaccines during one visit is very safe. Today’s vaccines are different than they were for our parent/grandparent’s generations making it safer than over to receive more vaccines​. 

10. What about kids with allergies or other health conditions 
Vaccines are safe for kids with most kinds of allergies. Getting vaccines may be especially important for children with certain health problems who can get very sick if they catch a disease. If your child has an allergy or any health condition, talk with your doctor. The doctor can tell you if any vaccine should be postponed or avoided. There is no link​ between developing asthma or allergies after receiving vaccines (Vaccine and Asthma or Allergies - Children's Hospital of Philadelphia). 

11. What about autism? ​
While some parents first notice signs of autism at about the same time their child gets vaccinated, the two events are not related. Dozens of scientific studies​ have concluded that there is no link between vaccines and autism. The following organizations have issued statements saying that there is no connection between vaccines and autism: Autism Science Foundation, American Academy of Pediatrics, National Academy of Medicine, Mayo Clinic, National Institutes of Health, World Health Organization​. 

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While the rates of autism continue to rise around the world, autism rates are no different among vaccinated and unvaccinated children. Other studies​ on autism suggest that children with autism have too many cells in a key area of the brain needed for communication, social and emotional development. This type of brain development occurs during the second trimester of pregnancy—long before a child gets any vaccinations. 

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In 1998, one study used falsified data to suggest a connection between the MMR vaccine and autism. After further investigation, the journal retracted the study, and the lead author lost his medical license. 

12. What ingredients are in vaccines? 
Some vaccine ingredients may sound like foreign substances, but they are familiar to your body. Here are the facts: 

• ​Aluminum is used in very small amounts to boost the body’s immune response, making the vaccines more effective. Aluminum also occurs naturally in soil, water, and air. During the first 6 months of life, your baby gets more aluminum from breast milk or formula, including soy formula, than from all vaccines combined! Aluminum does not build up, and most leaves the body within a couple of weeks. 
  
• Formaldehyde is sometimes used to keep vaccines germ-free, but it’s also produced naturally in the human body as a normal bodily function to produce energy. In fact, studies show that newborns weighing six to eight pounds already have 50-70 times more​​ formaldehyde in their bodies naturally than they would receive from a single dose of vaccine. 
  
• Thimerosal is a mercury-containing preservative that is no longer used​ in routine vaccines, except some forms of flu vaccine. Though no harm is known to have been caused by thimerosal in vaccines, as a precaution California law​ prohibits giving thimerosal-containing vaccines to pregnant women and children under age 3. Thimerosal-free flu vaccines are widely available. 
  

13. What about alternative schedules, getting vaccines later or spreading them out? 
Alternative schedules, skipping or delaying vaccines leaves your child at risk of catching serious diseases at younger ages—when these diseases are most dangerous. 

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The AAP immunization schedule​ offers some flexibility, allowing you to work closely with your child’s doctor to ensure the best care for your child. ​It’s important to know that spreading out vaccines outside of the AAP schedule is not based on scientific evidence. While it might seem comforting to space out the vaccines, research shows that this can instead be more stressful for your child. Plus, receiving multiple vaccines du​ring the same visit is safe and effective​. CDPH recommends vaccinating your child as soon as they are eligible to ensure they are protected as soon as possible against serious, yet preventable diseases. Your child’s health and well-being are the top priority, and sticking to the schedule helps provide the best protection against preventable diseases when your child is most vulnerable. 

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As a parent, you need to know the risks of skipping or delaying vaccines. So, talk to your doctor. Use reliable sources to make your decision. 
 
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Matthew’s Story 
Matthew’s parents decided their son could wait to get the vaccine against Hib disease, a disease they hadn’t heard about. Then one day Matthew complained of throat pain. “We thought it was strep throat and took him to the local hospital.” The doctor there diagnosed Hib disease and told them their son might die within minutes.  

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Learn more about Matthew’s story ​
 
Be choosy about what you read. ​We recommend these trusted sites: 

• ​Healthy Children 
  
• Children’s Hospital of Philadelphia (CHOP) Vaccine Education Center
  
• U.S. Dept. of Health and Human Services 
  
• Mayo Clinic Infant and Toddler Health
  
• Vaccinate Your Family 

Page last updated 9/8/2025

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