Vaccine Schedule: Other Schedule Issues

People often have other questions related to the schedule. To assist with finding answers, we have compiled relevant topics on this page, including:

  • Why vaccines are not approached in a “one-size-fits-all” manner
  • Why the vaccine schedule changes
  • What’s the “catch-up” schedule
  • What to know about missed vaccines
  • What’s the minimum time between doses
  • Topics related to schools and vaccines, including requirements and exemption types
  • What to know about package inserts
  • Finding immunization records
  • Why immunization registries are used

One size fits all

Some concerned about the safety of vaccines have argued that the schedule appears to be "one size fits all, failing to take into consideration an individual child’s special needs." Specifically, the concern is that the same vaccines are given to infants regardless of size, age or immunologic status. The following addresses these concerns.

Infants versus adults

A popular misperception is that all vaccines are given at the same dose to infants and adults. However, specific adult and pediatric versions of some vaccines are used, such as hepatitis A, hepatitis B, and tetanus, diphtheria, and pertussis vaccines. In the cases of hepatitis A and hepatitis B vaccines, adults receive greater quantities of the components that afford protection in order to produce a protective response. However, in the case of the latter vaccines, the quantities of components of the diphtheria and pertussis vaccines used in adults are less than those found in pediatric doses because adults are more likely to experience side effects from these vaccines.

Vaccines and medicines are not created equal

Sometimes, people are concerned about the dosing of vaccines because they compare them with medicines, which are given in different doses based on body weight. This is like comparing apples and oranges.

Specifically, medicines work when a certain level is present in the bloodstream; therefore, the weight of a person is important. It takes more of a medicine to see the same effect in a larger person than it does in a smaller person. This is similar to the effects of alcohol on a large man and a small woman.

Vaccines work differently. For a vaccine to be effective, the cells of the immune system are important. Immune cells, called T cells and B cells, must be able to recognize the component of the vaccine, so that if a person encounters that virus or bacteria again, these educated cells can become active and protect the person from an infection. Since these cells are present throughout the body, they are usually educated near where the vaccine is given and then the cells, not the vaccines, travel throughout the body. Because of the way that vaccines work, they typically require very low quantities of active ingredients.

Vaccine doses

Vaccine doses are not chosen arbitrarily. During the four phases of vaccine development, different doses are tested to determine the lowest effective dose for the target age group. For example, the rotavirus vaccine was tested at quantities as low as one-tenth the current dose and up to 10 times the current dose.

Vaccine developers must practice good medicine and good economics. Giving larger doses of active ingredients than required would increase the side effects from, and the costs, of vaccines.

Individuals and public policy

Another common belief is that individuals are not considered when public policies are made. However, numerous special circumstances are considered based on the patient’s medical history. This is why people are typically advised to get vaccines in their doctor's offices where their medical records can be reviewed prior to the administration of any vaccines.

Some patients require vaccines that are not necessarily recommended for their age group because they are at an increased risk of getting a disease. For example, children without a spleen or with an immune disorder called complement deficiency are recommended to get the meningococcal vaccine earlier than children without these conditions.

Special circumstances also exist for adults with weakened immunity resulting from radiation or certain medications. These patients should not receive vaccines containing live viruses, such as measles, mumps, rubella (MMR) or varicella (chickenpox). Likewise, children or adults with egg allergies typically should not receive the yellow fever vaccine, and children with severe gelatin allergies may need to forego certain immunizations.

You can find more about vaccines for particular groups in these handouts:

All 50 states allow individuals to forego immunizations that are not safe for them based on their medical histories.

Why does the vaccine schedule change?

Changes to the immunization schedule can be the result of:

  • New or different vaccines — e.g., HPV vaccine for girls in 2006 or acellular pertussis vaccine in 1997
  • Changes to the group of people most susceptible to the disease — e.g., hepatitis A vaccine in 2006
  • Changes to the virus — e.g., H1N1 influenza vaccine in 2009
  • New information — e.g., HPV vaccine for boys in 2011

Scientists and public health officials are dedicated to understanding and monitoring diseases and the vaccines being used to prevent them. As a result, the immunization schedule is updated regularly. For this reason, it is a good habit to check with your healthcare provider at every visit about whether you or your family members should get any vaccines.

What is the “catch-up” schedule?

If doses of vaccine need to be delayed or are missed, the catch-up schedule gives healthcare providers the information necessary to safely get a child up to date. Vaccines may have been missed due to vaccine shortages, new or revised vaccine recommendations, missed visits (such as during the COVID-19 pandemic), or changes in health status that no longer make previous contraindications or precautions necessary. A good habit to develop is to check with your healthcare provider during every visit whether any vaccines are necessary and can be given.

Missed vaccines

Vaccines are given as a series of shots during a scheduled period of time (see Vaccine Schedule - Timetable). However, if a shot is missed, you do not need to start the series of doses all over again. The series can be continued as usual, simply picking up where you left off. Part of the immunization schedule is titled the “catch-up” schedule to help doctors most efficiently get kids who missed multiple vaccines back on schedule.

Minimum time between doses of vaccines

In addition to vaccines being given at particular ages according to the recommended immunization schedule, healthcare providers must also follow guidelines related to how soon additional doses of the same or different vaccines can be given. These guidelines were developed based on the types of vaccines and how our immune systems respond to them. For example, more than one live weakened viral vaccine (e.g., MMR and chickenpox) can be given during the same visit, but if one is given and the other is not, the second one cannot be given until at least four weeks later. Studies of simultaneous administration have shown that the immune response to both vaccines is similar if they are given in the same visit or individually; however, if chickenpox was given less than four weeks after MMR vaccine, fewer people became immune to chickenpox than if the vaccines were given more than four weeks apart. Similar studies have been conducted for other vaccines on the schedule.

Scheduling appointments: A parent’s question

Q. My infant received vaccines at his 4-month check-up. He is scheduled to receive more vaccines at his 6-month check-up, but it is scheduled for only seven weeks from his last visit. Is this safe? 

A. Vaccines on the schedule are recommended to be given two months apart; however, all vaccines also have what are known as “minimum intervals.” These are the required amounts of time that must pass between doses of vaccine. Minimum intervals between doses of vaccines are determined when the vaccine is developed by studying the immune response to each dose to make sure that the response from a previous dose won’t interfere with the response to the next dose. For the vaccines typically given at 4 and 6 months of age, the minimum amount of time required is four weeks, so your son’s appointment will meet this standard.

Schools and vaccine requirements

School entry requirements

Are you unsure about which vaccines are required for your child to enter school? Are you going to be moving to a new state and need to check on vaccine requirements? The Immunization Action Coalition (IAC) has gathered all of this information into one place for you.

Exemptions and herd immunity

Some parents are confused about whether their children need vaccines. They may have heard, incorrectly, that vaccines cause autism or other chronic conditions. Maybe they are concerned that the vaccines were made using aborted-fetal tissue, or they may feel that vaccines are not necessary because they haven't seen anyone they know affected by the diseases that vaccines prevent.

In most states, vaccines are required for entry into school or childcare centers. However, there are cases in which a child may be able to go to school without having a particular vaccine. In these cases, the parent must exercise an "exemption," which is a legal option to forego a vaccine.

Different states have different laws regarding exemptions. Three kinds of exemptions are available:

Medical exemptions

Medical exemptions are allowed when a child has a medical condition or allergy that may make receiving the vaccine dangerous. All 50 states allow medical exemptions. For school entry purposes, these exemptions typically require a physician's note supporting the medical necessity of the exemption.

Religious exemptions

Religious exemptions are allowed when immunizations are not in agreement with the parents' religious beliefs. Forty-three of the 50 states allow these exemptions.

Philosophical (or personal) exemptions

Philosophical exemptions are allowed when non-religious, but strongly held beliefs, prevent a parent from allowing their child to be immunized. Eighteen states allow some type of philosophical exemption.

In certain situations, an exemption can be challenged by the state. These situations include those that would put the child at a higher risk of disease than is reasonable (medical neglect) or those that would put society at risk (e.g., epidemic situations). Also, in some states, if an unvaccinated child is found to transmit a vaccine-preventable disease to someone else, the parents may be liable in a civil suit.

Because vaccines are considered medically necessary (except in the medical cases mentioned above), they are considered to be "best-care" practices. Therefore, if parents choose not to immunize their children, doctors will often have them sign a statement that they have discussed the risks and benefits of the vaccines and they understand that they are taking a risk in refusing vaccines for their children.

Risking disease

Many people incorrectly assume that a choice not to get a vaccine is a risk-free choice. But it isn't. The choice not to get a vaccine is a choice to risk the disease that the vaccine prevents. Studies have shown that unimmunized children are more likely to get vaccine-preventable diseases if there is an outbreak, compared with those who have been immunized. Unimmunized children may also be barred from school during an outbreak to protect them from the disease.

Here are some things to consider before making a decision not to immunize your child:

  • Vaccines are considered the best way to protect your child against diseases that could cause liver damage, liver cancer, suffocation, meningitis, pneumonia, paralysis, lockjaw, seizures, brain damage, deafness, blindness, mental retardation, learning disabilities, birth defects, encephalitis or death.
  • Vaccines are studied extensively for their safety before being recommended for children and continue to be monitored after recommendation (See Making Vaccines: Process of Vaccine Development). Because vaccines are given to healthy children, they are held to the highest standards of safety.
  • Vaccines are considered by some to be a civic duty because they create "herd immunity." This means that when most of the people in a community are immunized, there is less opportunity for a disease to enter the community and make people sick. Because there are members of our society who are too young, too weak, or otherwise unable to receive vaccines for medical reasons, they rely on "herd immunity" to keep them well.

Harm to others

People in the community may be harmed by a parent's decision not to immunize their child in four ways:

  • If the unimmunized child gets a preventable disease, he or she may pass that disease to other unimmunized people in the community.
  • Even when people are immunized, there is always a small percentage for whom the vaccine did not work or their immunity has waned; so these people will also be at increased risk if an unimmunized child gets a preventable disease.
  • If a person cannot receive vaccines for medical reasons, they rely on those around them for protection from the diseases.
  • Families that have received vaccines and contract a vaccine-preventable disease from an unimmunized person will need to pay the medical costs incurred by the disease. Treatment for the diseases costs much more than the vaccines, so the unimmunized child's family or society will bear these costs.

Those who choose not to immunize their child may be considered "free riders" by those who have immunized their children. For example, a mother whose son experienced a severe bout with pertussis was angry that other children in the classroom were not immunized. In discussing vaccine safety as the reason that many parents give for not wanting to immunize, she wondered why their children should be protected by herd immunity when her child and all of the other immunized children bore the small risk of side effects. In addition, she wondered why she wasn't made aware that so many of the children in the school weren't immunized due to personal beliefs. She concluded by saying, "Had I known … I would never have enrolled him in that school." 

Downloadable resource

Vaccinated or Unvaccinated: What you should know

Video resources

"What Vaccines Might My Child Need Before Starting School?"

"Why Are Vaccines Required Before My Child Goes to School?"

"How Do I Know If Other Children in My Child's Class Have Been Immunized?"

Vaccine recommendations and package inserts

I understand that the information included with a vaccine sometimes differs from more commonly available information. Can you explain why?

While a package insert provides information about the vaccine, it is important to realize that it is being provided by the company and, therefore, has legal requirements that must be followed in its preparation. During the development of a vaccine, safety studies are completed by comparing a group of people who received the vaccine with a group of people who did not, called the placebo group. If a side effect occurs more times in the vaccine group, it may be a result of the vaccine. However, the company, according to the Food and Drug Administration (FDA), must report any side effects that occurred in the vaccine group, even if the number of occurrences was similar to or the same as those in the placebo group. All of these side effects are then listed in the package insert. (See “Phase III trials” section on the “Process of Vaccine Development” page for examples of placebo-controlled studies.)

Groups that make recommendations about vaccines, such as the Centers for Disease Control and Prevention (CDC), the American Academy of Pediatrics (AAP) and the American Academy of Family Physicians (AAFP), don't use the same criteria as often appear in package inserts to determine whether a side effect is caused by vaccines. When these groups make recommendations, they apply scientific criteria to data review, allowing them to determine whether a particular side effect occurs more often in the vaccine group than the placebo group. If it does, these side effects are likely to be related to receipt of the vaccine and are listed in educational materials to physicians. For this reason, the number of side effects listed in the package insert is much greater than that listed by the CDC, AAP or AAFP, but the side effects indicated in the educational materials provided by these groups more accurately reflect the findings of the scientific studies.

Immunization records

Q. I recently moved to the U.S., and my son is now starting school. I have been asked to show an immunization record, but I do not have one. How can I get one? 

A. First, you should start by contacting your child’s previous healthcare providers to see if they have a copy. If you are still unable to locate a record, your doctor may consider your son to have had no immunizations and begin the appropriate immunization schedule.

Even if your son had some vaccines previously, the additional doses will not hurt him.

Alternatively, the doctor may give your son a blood test to see if he is immune to certain diseases, such as measles, mumps, rubella, chickenpox, tetanus, diphtheria, hepatitis A, hepatitis B and polio. This may reduce the number of vaccines your son needs to get, but he may still require other vaccines depending on age and other factors.

Q. I need proof of immunizations for a job, but I do not have the dates that I was immunized. Is there a chart available based on the year you were born?

A. This type of chart is not available. Even if a particular vaccine was available when you were born, it does not mean that you received it. Many factors can contribute to whether you got a certain vaccine including, among others, whether it was required, whether your doctor had it, and whether your parents took you to get it.

If you are unsuccessful in locating your records, you may be able to get a blood test to help determine the diseases to which you are immune. In some cases, your healthcare provider may simply recommend getting the vaccines since an extra dose would not be harmful. 

For additional information about locating old immunization records, check this resource from the Immunization Action Coalition.

Immunization registries

An immunization registry is a confidential computerized information system that tracks which vaccines have been given to an individual. One of the goals of the Healthy People 2030 initiative is to increase the number of immunization registries that track adult vaccinations.

How will participation in a registry benefit my child?

Registries allow healthcare professionals to provide better care for your family because all of an individual’s immunization information is stored in one place. If you visit more than one doctor, change health insurance providers, no longer have access to records from a previous doctor, or are physically displaced, such as occurred to families after Hurricane Katrina in 2005, immunization records will remain up to date and intact.

In the aftermath of Katrina, many children were relocated to different states where they attended schools that required proof of immunization. Most families did not have their medical records and family doctors could not be reached to forward the records. Because registries were in place in some of the affected areas, those families had less difficulty getting their children back to school.

Another benefit of registries is that they ensure timely immunizations through reminders to parents and healthcare professionals. In addition, registries prevent unnecessary (duplicative) immunizations because there is a complete, official copy of a child's immunization history when needed by other healthcare professionals or to provide to schools, day cares and camps.

What are the concerns about registries and how are they being addressed?

Concerns about registries focus on maintaining confidentiality and preventing misuse of information by outside agencies. However, families can be reassured for several reasons:

  • First, privacy and confidentiality have come to the forefront in medical institutions as they comply with the Health Insurance Portability and Accountability Act of 1996 (HIPAA) and move toward electronic medical records for their patients.
  • Second, any information reported about immunizations is only reportable from a population standpoint, so at no time can an individual's immunization status be shared with outside sources. Further, systems have been established that assure parental knowledge and consent for participation in a registry. This affords parents the opportunity to learn about the registry in their area.

Reviewed by Paul A. Offit, MD on September 06, 2022

Materials in this section are updated as new information and vaccines become available. The Vaccine Education Center staff regularly reviews materials for accuracy.

You should not consider the information in this site to be specific, professional medical advice for your personal health or for your family's personal health. You should not use it to replace any relationship with a physician or other qualified healthcare professional. For medical concerns, including decisions about vaccinations, medications and other treatments, you should always consult your physician or, in serious cases, seek immediate assistance from emergency personnel.