Frequently Asked Questions about Immunization 

As a parent, you want to make the best decisions to protect your child - staying informed will help. Your questions are important, and you deserve reliable information to support your decisions. If you want to learn more, ask your doctor for a “consultation visit,” or check out the websites at the end.

1. Are Vaccines safe?

Yes. Vaccines are very safe.* In fact, experts including the American Academy of Pediatrics, the National Academy of Medicine, and the World Health Organization agree that vaccines are even safer than vitamins. Millions of children and adults are vaccinated every year—safely. Thousands of people take part in clinical trials to test a vaccine before it is licensed by the Food and Drug Administration (FDA). After it’s licensed, the Vaccine Adverse Events Reporting System (VAERS) helps track any health effect that happens 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 vaccines are safe.


2. What kind of side effects should I know about?

Any medicine can cause reactions in some people. The most common side effects from vaccines are swelling or tenderness at the injection site and fever. Serious allergic reactions are very rare, happening in about 1 person out of a million* shots given. 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.


3. Why do children today get so many immunizations?

Thirty years ago, vaccines protected young children from only seven diseases. Today, we can protect them from at least 14 dangerous diseases because of medical advances. Many shots are also “boosters” of the same vaccine to give children the best protection possible.


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 a 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, for instance, is still common in Europe, Africa, and Asia. Travelers can catch measles while overseas and spread it in Colorado.
  • Whooping cough (pertussis) cases were a serious issue for schools in Boulder County (and across Colorado) over the last few years.
  • 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 and breastfeeding?

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 whooping cough, measles, mumps, and other diseases. Breastfeeding is very healthy for your baby, but breastfeeding alone cannot fully protect babies from diseases like whooping cough or measles. Also, most antibodies passed on from moms to babies during pregnancy do not last beyond infancy.4


6. 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 not the disease. Most vaccines are over 99% effective in preventing illness.


7. Is it safe for a child’s immune system to have multiple shots?

Yes. Children are exposed to hundreds of viruses and bacteria5 during normal activities like eating and playing. Getting vaccines is no extra burden on the immune system—even for babies.6 Getting combination vaccines, like MMR (that protects against measles, mumps, and rubella), or getting multiple shots during one visit is very safe. Today’s vaccines are more refined, so even though kids receive more vaccines, they receive far fewer antigens overall7 (compared to their parents or grandparents).


8. What about kids with allergies or other health conditions?

Vaccines are safe for kids with most kinds of allergies.8 Getting shots 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.


9. 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 studies9 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, and National Center for Complimentary and Integrative Health.

While the rates of autism continue to rise around the world, autism rates are no different in vaccinated and unvaccinated children.10 Recent 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.11,12 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.


10. 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 shots 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 formula13 than from all shots 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 more14 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 used15 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 law16 prohibits giving thimerosal-containing vaccines to pregnant women and children under age 3. Thimerosal-free flu vaccines are widely available.


11. What about getting shots later or spreading them out?

Skipping or delaying shots leaves your child at risk of catching serious diseases at younger ages— when these diseases are most dangerous. That’s why most doctors follow the CDC’s recommended immunization schedule, which is based on independent medical science review and updated each year. The schedule on the back of this fact sheet follows CDC’s recommendations and helps you keep track of your child’s immunizations. Advice to spread out shots is not based on science.17 Spreading out shot visits may make you feel more comfortable, but it’s no help to your child. Research shows that getting several shots at the same visit is safe.18 Spreading out shots may actually be more stressful for your child. 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.


12. Can a baby’s immune system easily handle the vaccines recommended for infants and toddlers?

A baby’s immune system can easily handle the vaccines recommended for infants and toddlers. Some people worry that receiving too many vaccines early in life can overwhelm a baby’s immune system and that this might somehow lead to autism. This doesn’t fit with what we know about the remarkable capacity of the immune system. From the moment of a baby’s birth, the immune system begins coping with microorganisms in the form of bacteria, viruses, and fungi. Like vaccines, these microorganisms contain foreign antigens – proteins that stimulate the immune system. When you realize that a single bacterium contains a larger variety and number of antigens than are found in all the recommended early childhood vaccines combined, you can see that a baby’s immune system, which copes with exposure to countless bacteria each day, can easily withstand exposure to the antigens in vaccines.


13. Should I get the flu shot?

In general, your immune system is dialed down a bit in pregnancy. But interestingly enough, your pregnant immune system may actually respond more intensely in certain situations. And how you respond to the influenza virus is one of those situations. It is thought that this altered immune response, along with changes in how your heart and lungs work, are why pregnant women who get the flu often have much more severe symptoms, serious complications, and can even die from the infection. There is also some evidence that having the flu in the first several weeks of pregnancy might be associated with an increased risk of your baby being born with certain birth defects.

Put the risk of severe complications from the flu together with the relative low risk of the flu vaccine, and it’s easy to understand why getting the flu shot during pregnancy is so strongly recommended. Getting vaccinated against the flu during pregnancy has benefits for your baby as well. Newborns, like pregnant women, are more likely to get seriously ill or even die if they get the flu. Your baby can’t get a flu shot until 6 months of age. However, if you get the flu vaccine during pregnancy you will pass antibodies to your baby that will protect him or her from the flu in the first few months of life. This is especially important for babies that will be born during flu season (between October and May).


Q1-11 adapted from Vaccine Safety: Answers to Parents’ Top Questions from CDPH (see footnotes)

Q12 References

  • Offit PA, Quarles J, Gerber MA, et al. Addressing parents’ concerns: do multiple vaccines overwhelm or weaken the infant’s immune system? Pediatrics. 2002;109(1):124–129. abstract/109/1/124
  • Vaccine Education Center, Children’s Hospital of Philadelphia. Too Many Vaccines? What You Should Know. Available at articles/vaccine-education-center/too-many-vaccines.pdf

Q13 Reference -


more information about how maternal pertussis (Whooping cough) vaccination reduces risk for newborns by more than 90%:

more information about the topic of the MMR vaccine and autism:

Too Many Vaccines? What You Should Know

A great comic book overview of vaccines:


If you are looking for additional information, we recommend these trusted sites:

American Academy of Pediatrics
Centers for Disease Control and Prevention (CDC)
Children’s Hospital of Philadelphia
Evaluating Health Information on the Web
Immunize for Good
Mayo Clinic
Parents of Kids with Infectious Diseases
Thimerosal FAQs
U.S. Dept. of Health and Human Services
Vaccines: Calling the Shots (PBS documentary)
Voices for Vaccines



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