Immunization

Vaccines are one of the most successful public health initiatives in history. Millions of lives have been saved through immunization since the advent of the smallpox vaccine in the late 18th century.

The Language of Immunization

Vaccination vs. immunization: Although these terms are very similar and often used interchangeably, “vaccination” refers to the administration of a vaccine and “immunization” is the process of making someone immune, either from vaccination (although vaccination does not guarantee immunity) or from natural disease exposure.

Active vs. passive immunity: Active immunity occurs when the body produces antibodies in response to a disease-specific antigen, either through exposure to the disease (natural immunity) or through exposure to vaccination (vaccine-induced immunity). Passive immunity occurs when a person is given antibodies against a disease. The antibodies are preformed and immediately active. They do not stimulate the body to make its own antibodies and therefore the immunity conferred is short-lived. Use of passive immunity is much less common than inducing active immunity. Examples of passive immunization include tetanus immune globulin, hepatitis B immune globulin, and palivizumab for respiratory syncytial virus (RSV).

Live vs. inactivated vaccinations: Vaccine-induced immunity can be achieved either through live or inactivated vaccinations. Live vaccines contain a living but significantly weakened (attenuated) version of the virus or bacteria and induce immunity that is closer to natural immunity. However, live vaccines pose a risk for people with weakened immune systems. See the guidelines from the Centers for Disease Control and Prevention (CDC) regarding specific contraindications to live vaccines for specific medical conditions. Inactivated vaccines contain a killed version of the pathogen, and are generally considered safer and more stable than live vaccines, but stimulate a weaker immune response.

Vaccine Recommendations

Recommendations: The Advisory Committee on Immunization Practices (ACIP), a committee of the CDC, as well as the American Academy of Pediatrics (AAP) and the AAFP (American Academy of Family Physicians), reviews and updates immunization schedules annually. Vaccine recommendations are based on available evidence on vaccine efficacy, safety, immunogenicity, and disease prevalence. The vaccine schedules are published in Morbidity and Mortality Weekly Report (MMWR) and are available on the CDC website.

Vaccine Information Statements (VISs): VISs are published by the CDC for every vaccine and detail the purpose of the vaccine, the expected benefits, and associated risks. Federal law requires clinicians to provide a VIS to patients or parents for each vaccine, each time one is administered.

Covid-19 vaccine: ACIP recommends use of Covid-19 vaccines for everyone aged 6 months and older. Covid-19 vaccine and other vaccines may be administered on the same day (see Interim COVID-19 Immunization Schedule).

Primary Vaccine Schedule

The primary schedule is the recommended vaccine schedule for first-time immunization for immune-sufficient children ages 0 to 18 years. Some immunizations are administered during a specific age range. Each practice likely has an agreed-upon schedule to ensure essential vaccines are administered and not missed.

These recommendations must be read with the Notes. To make vaccination recommendations, health care providers should:
1. Determine recommended vaccine by age (Table 1)
2. Determine recommended interval for catch-up vaccination (Table 2)
3. Assess need for additional recommended vaccines by medical condition or other indication (Table 3)
4. Review vaccine types, frequencies, intervals, and considerations for special situations (Notes)
5. Review contraindications and precautions for vaccine types (Appendix)
6. Review new or updated ACIP guidance (Addendum)
(Source: Child and Adolescent Immunization Schedule by Age: Recommended Child and Adolescent Immunization Schedule for ages 18 years or younger, United States, 2024. Centers for Disease Control and Prevention 2024.)

Catch-up vaccine schedule: The catch-up schedule is a recommended schedule for administering routine vaccinations for children who are un- or undervaccinated. This schedule includes the minimum dose-interval ranges for administration. Immigrant children are a subset of patients for whom the catch-up schedule is often particularly important. The catch-up schedule is published and updated annually along with the primary vaccine schedule.

Contraindications, Precautions, and Adverse Events

Contraindications and precautions: The CDC defines contraindications as conditions in a recipient under which vaccines should not be administered because the condition increases the risk for a serious adverse reaction to vaccination. A precaution is a condition in a recipient that might increase the risk for a serious adverse reaction, might cause diagnostic confusion, or might compromise the ability of the vaccine to produce immunity. Refer to CDC guidelines for complete information on contraindications and precautions.

• Anaphylaxis to a previous dose of the same vaccine, or to a vaccine component, is the only contraindication shared by all vaccinations.

  • Moderate-to-severe acute illness is a precaution common to all vaccines in which the benefits may outweigh the risk.

  • Mild illness, as is common in young children, is not a precaution or contraindication. Deferring vaccines without a true contraindication or precaution leads to missed opportunities to vaccinate.

  • Some live vaccines are contraindicated in patients with immunodeficiencies or who are on immunomodulating medications (for specific recommendations, see the guidelines for contraindications and precautions).

  • Information about each vaccine can be found on the vaccine package insert approved by the Food and Drug Administration (FDA).

Adverse events: Fever and local reaction (including pain, redness, and swelling) are the most common adverse events associated with vaccines. An antipyretic should not be given preemptively because of concern that it may decrease immunogenicity. That said, if a patient is symptomatic with fever or pain, administration of medication such as acetaminophen is acceptable.

The following table summarizes common adverse events, contraindications, and precautions associated with commonly used vaccines. Refer to ACIP guidelines for complete information on contraindications and precautions.

VAERS (Vaccine Adverse Event Reporting System)

• VAERS is a passive, post-market reporting system comanaged by the CDC and the FDA.

• Serious adverse events should be reported to VAERS even if causality is not clear.

• Anyone can report an adverse event to VAERS, including the public.

• Health care professionals are required to report certain adverse events.

• Vaccine manufacturers are required to report all adverse events that come to their attention.

Vaccines for Special Circumstances

Travel: Make sure the child is up to date on all routine vaccinations.

• For very young children, some routine vaccines can be administered early (see Travelers’ Health on the CDC website).

• Travel recommendations for specific countries and exposure risk, including vaccination recommendations, can be found on the CDC Yellow Book: Health Information for International Travel and the Pre-Travel Providers’ Rapid Evaluation Portal (Pre-Travel PREP) website.

Rabies exposure: Rabies is a severe, life-threatening disease caused by a virus transmitted by the saliva of an infected animal. Rabies vaccination may be given prophylactically if a patient is at high risk of exposure (e.g., travel to certain regions of the world or work with high-risk wild animals). More often, rabies vaccination is given after a known or possible rabies exposure. Common exposures of concern include bat bites or bites from an unknown dog that cannot be followed up. After exposure, the vaccine series includes four doses given over 2 weeks (days 0, 3, 7, and 14) as well as rabies immunoglobulin given on day 0.

Bacillus Calmette-Guérin (BCG): The BCG vaccine is a live bacterial vaccine against tuberculosis (TB). It is administered to infants living in a setting with a high TB prevalence. The goal is to prevent early-onset TB, especially tuberculous meningitis, but BCG does not prevent TB entirely. Foreign-born children who have been vaccinated with BCG should not be considered TB immune, and BCG status needs to be considered when interpreting a tuberculin skin test (TST or purified protein derivative [PPD]).

Immunocompromised patients: Children who have received a transplant, are undergoing chemotherapy, or have an inherited or acquired immunodeficiency require special consideration in their vaccination planning (see the CDC Immunization Schedule by Medical Indication). Inactivated vaccines are safe to administer to immunocompromised patients, but they may have a suboptimal response. Understanding immune status and recovery is important when planning vaccinations. Live vaccines, viral or bacterial, should not be given to children with severely compromised immune systems.

Household and other close contacts of patients with compromised immune systems should receive all other age-appropriate vaccines, including the live oral rotavirus vaccines. The risk of acquiring and transmitting a vaccine-preventable illness is greater to someone with an immunodeficiency than the risk of the vaccine causing harm through transmission.

Post-IVIG: If a patient receives intravenous immunoglobulin (IVIG), the effectiveness of live virus vaccines given 2 weeks prior or 1 to 2 months after may be decreased. IVIG suppresses the response to the measles vaccine in particular; measles-mumps-rubella (MMR) vaccine should be administered 8 to 12 months after IVIG. Do not test for immunity after administration of IVIG because the patient will acquire passive immunity from the donor immunoglobulin. Testing may not be reliable for 6 to 12 months after IVIG administration.

Vaccines and Society

Vaccine hesitancy: Some parents have very specific concerns about vaccines, while others have vague misgivings or hesitancy, and a small proportion have major objections to vaccinating their child. To maintain a therapeutic alliance, it is important to understand and address these concerns. The best evidence on addressing vaccine hesitancy is to provide clear, simple, repeated endorsements of the standard vaccine schedule. Parents with specific fears may appreciate an explanation of the evidence that supports or refutes their fears. Be familiar with the most common fears and be prepared to answer questions about these concerns. (See Addressing Vaccine Hesitancy and How to Communicate With Vaccine-Hesitant Parents for more information on this topic.) The CHOP Vaccine Education Center provides information about specific vaccine components to help address parental questions and concerns.

Common concerns about vaccines include:

• autism

• antigen load and the immune system

• pain of administration

• vaccine combinations

• herd immunity: all risk and no benefit?

• the flu shot causing the flu

• HPV immunization and sexual debut

• insufficient data (Covid-19)

• government control

Vaccine exemptions: States mandate vaccines for high-risk diseases in child care and public-school settings. Laws regarding exemptions vary from state to state. Medical exemptions exist for children who have contraindications to a specific vaccine (e.g., live virus vaccines for immunocompromised patients). Nonmedical exemptions include religious beliefs or personal philosophy. The AAP recommends elimination of all nonmedical exemptions.

Vaccine refusal and ethics: Vaccines are associated with many ethical considerations from the public health and policy perspective. One of the most common ethical concerns for the individual practitioner or clinic is whether to dismiss a vaccine-refusing family from your practice.

Vaccine refusal is a challenge to clinical practice. Vaccines have revolutionized pediatric care, and pediatricians want all patients to be adequately protected from vaccine-preventable illnesses. Dismissing a family can result in reduced access to needed health care or replacement with a provider who is supportive of vaccine avoidance, increasing the likelihood that the child will remain undervaccinated.

For these reasons, the AAP recommends against dismissal of vaccine-refusing families. If a clinician cannot provide care for a family, it is their responsibility to ensure that the family has established adequate care with another provider before ending care. The AAP provides a documentation form that can be used for charting when families refuse vaccine(s).