Immunity can be achieved
Actively by using antigens (eg, vaccines, toxoids)
Passively by using antibodies (eg, immune globulins, antitoxins)
A toxoid is a bacterial toxin that has been modified to be nontoxic but that can still stimulate antibody formation.
A vaccine is a suspension of whole (live or inactivated) or fractionated bacteria or viruses rendered nonpathogenic.
Vaccination has been extremely effective in preventing serious disease and in improving health worldwide. Because of vaccines, infections that were once very common and/or fatal (eg, smallpox, polio, diphtheria) are now rare or have been eliminated. However, except for smallpox, these infections still occur in medically underserved parts of the world.
Effective vaccines are not yet available for many important infections, including
Most sexually transmitted infections (eg, HIV infection, herpes, syphilis, gonorrhea, chlamydial infections)
Tick-borne infections (eg, Lyme disease, ehrlichiosis and anaplasmosis, babesiosis)
Many tropical diseases (eg, Chagas disease)
Many emerging diseases (eg, West Nile virus infection, Zika virus infection)
As of October 2023, the World Health Organization (WHO) recommends widespread use of the RTS,S/AS01 (RTS,S) and R21/Matrix-M malaria vaccines among children living in malaria endemic areas with moderate to high Plasmodium falciparum malaria transmission (see WHO: Malaria vaccine implementation programme).
For the contents of each vaccine (including additives), see that vaccine's package insert.
Vaccines in the United States
The most current recommendations for routine immunization in the United States are available at the Centers for Disease Control and Prevention (CDC) web sites Child and Adolescent Immunization Schedule by Age and Adult Immunization Schedule by Age and as a free mobile app. For a summary of changes to the 2024 adult immunization schedule, see the Advisory Committee on Immunization Practices Recommended Adult Immunization Schedule, United States, 2024. (See also table Vaccines Available in the United States).
Despite clinical guidelines and the burden and consequences of vaccine-preventable diseases, some adults do not receive the recommended vaccines. In the United States, vaccination coverage among adults remains low for most vaccines. In addition, coverage for all vaccines differs by race and ethnicity with generally lower coverage among Black and Hispanic adults compared with White adults (see CDC: Vaccination Coverage among Adults in the United States, National Health Interview Survey, 2021).
Vaccine Administration
Vaccines should be given exactly as recommended on the package insert. Noncompliance or other factors may result in changes in vaccine schedule for individual patients; for most vaccines, the interval between a series of doses may be lengthened without losing efficacy. If a vaccine series (eg, for hepatitis B or human papillomavirus) is interrupted, clinicians should give the next recommended dose the next time the patient presents, provided that the recommended interval between doses has passed. They should not restart the series (ie, with dose 1).
Injection vaccines are usually given intramuscularly into the midlateral thigh (in infants and toddlers) or into the deltoid muscle (in school-aged children and adults). Some vaccines are given subcutaneously. For details on vaccine administration, see the General Best Practice Guidelines for Vaccine Administration from the Advisory Committee for Immunization Practices (ACIP), Administering Vaccines to Adults from the Immunization Action Coalition, and CDC: Administer the Vaccine(s).
For patients with upper extremity lymphedema (eg, breast cancer patients), best practice is to use the other arm or an alternate location.
Shoulder injury related to vaccine administration (SIRVA) may be caused by the unintentional injection of a vaccine into tissues and structures under the deltoid muscle of the shoulder (1).
Clinicians should have a process in place to ensure that patient vaccination status is reviewed at each visit so that vaccines are given as per recommendations. Patients (or caregivers) should be encouraged to keep a history (written or electronic) of their vaccinations and share this information with new health care professionals and institutions to make sure that vaccinations are up to date.
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Simultaneous administration of different vaccines
With rare exceptions, simultaneous administration of vaccines is safe, effective, and convenient; it is particularly recommended when children may be unavailable for future vaccination or when adults require multiple vaccines before international travel. An exception is simultaneous administration of pneumococcal conjugate vaccine and the meningococcal conjugate vaccine MenACWY-D (Menactra) to children with functional or anatomic asplenia; these vaccinations should not be given during the same visit but should be separated by ≥ 4 weeks.
Simultaneous administration may involve combination vaccines (see table Vaccines Available in the United States) or use of ≥ 1 single-antigen vaccines. More than one vaccine may be given at the same time using different injection sites and syringes.
If live-virus vaccines (eg, varicella and measles-mumps-rubella [MMR]) are not given at the same time, they should be given ≥ 4 weeks apart.
Vaccine administration reference
1. Barnes MG, Ledford C, Hogan K: A "needling" problem: Shoulder injury related to vaccine administration. J Am Board Fam Med 25(6):919–922, 2012. doi: 10.3122/jabfm.2012.06.110334
Restrictions, Precautions, and High-Risk Groups
Restrictions and precautions are conditions that increase the risk of an adverse reaction to a vaccine or that compromise the ability of a vaccine to produce immunity. These conditions are usually temporary, meaning the vaccine can be given later. Sometimes vaccination is indicated when a precaution exists because the protective effects of the vaccine outweigh the risk of an adverse reaction to the vaccine.
Contraindications are conditions that increase the risk of a serious adverse reaction. A vaccine should not be given when a contraindication is present.
Allergy
For many vaccines, the only contraindication is a serious allergic reaction (eg, anaphylactic reaction) to the vaccine or to one of its components.
Egg allergy is common in the United States. Some vaccines produced in cell culture systems, including most influenza vaccines, contain trace amounts of egg antigens. CDC guidelines for the influenza vaccine state patients with a history of egg allergy should be given the influenza vaccine. An egg allergy necessitates no additional safety measures for influenza vaccination beyond those recommended for any recipient of any vaccine, regardless of severity of previous reaction to egg. Any influenza vaccine that is otherwise recommended based on the recipient’s age and health status can be used. (See CDC: Summary: ‘Prevention and Control of Seasonal Influenza with Vaccines: Recommendations of the Advisory Committee on Immunization Practices (ACIP)—United States, 2023-24’.)
Guillain-Barré syndrome
Patients who developed Guillain-Barré syndrome (GBS) within 6 weeks after a previous influenza or diphtheria-tetanus-acellular pertussis (DTaP) vaccination may be given the vaccine if the benefits of vaccination are thought to outweigh the risks. For example, for patients who developed the syndrome after a dose of DTaP, clinicians may consider giving them a dose of the vaccine if a pertussis outbreak occurs; however, such decisions should be made in consultation with an infectious disease specialist.
The Advisory Committee on Immunization Practices no longer considers a history of GBS to be a contraindication or precaution for use of the meningococcal conjugate vaccine, although it remains listed as a precaution in the package insert (see CDC: Meningococcal Vaccines Safety Information).
Fever or other acute illness
A significant fever (temperature of > 39° C) or severe illness without fever requires delaying vaccination, but minor infections, such as the common cold (even with low-grade fever), do not. This precaution prevents confusion between manifestations of the underlying illness and possible adverse effects of the vaccine and prevents superimposition of adverse effects of the vaccine on the underlying illness. Vaccination is postponed until the illness resolves, if possible.
Pregnancy
Immunocompromise
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Patients with HIV infection
Asplenia
Asplenic patients are predisposed to overwhelming bacteremic infection, primarily due to encapsulated organisms such as Streptococcus pneumoniae, Neisseria meningitidis, or Haemophilus influenzae type b (Hib). Asplenic adults should be given the following vaccines (before splenectomy if possible):
Hib conjugate vaccine: Patients are given a single dose and no booster.
Meningococcal conjugate vaccine (MenACWY): Patients are given 2 doses at least 8 weeks apart and a booster every 5 years.
Meningococcal B vaccine (MenB): Patients are given a 2-dose series of MenB-4C ≥ 1 month apart or a 3-dose series of MenB-FHbp at 0, 1 to 2, and 6 months (if dose 2 was given at least 6 months after dose 1, dose 3 is not needed; if dose 3 was given < 4 months after dose 2, a fourth dose should be given at least 4 months after dose 3); MenB-4C and MenB-FHbp are not interchangeable (use same product for all doses in series); 1 dose MenB booster 1 year after primary series and revaccinate every 2 to 3 years if risk remains. Pregnancy: Delay MenB until after pregnancy unless at increased risk and vaccination benefits outweigh potential risks.
Pneumococcal conjugate (PCV15 and PCV20) and pneumococcal polysaccharide (PPSV23) vaccines: Patients are given one dose of PCV20 or one dose of PCV15 followed by a dose of PPSV23 if they have not previously received a pneumococcal conjugate vaccine or if their vaccination history is unknown. A minimum interval of 8 weeks between PCV15 and PPSV23 can be considered for adults with an immunocompromising condition (including congenital or acquired asplenia), cochlear implant, or cerebrospinal fluid (CSF) leak.
Additional doses may be given based on clinical judgment.
Transplantation
Before solid organ transplantation, patients should receive all appropriate vaccines. Patients who have had allogeneic or autogeneic hematopoietic stem cell transplantation should be considered unimmunized and should receive repeat doses of all appropriate vaccines. Care of these patients is complex, and vaccination decisions for these patients should involve consultation with the patient's hematologist-oncologist and an infectious disease specialist.
Blood product use
Live-microbial vaccines should not be given simultaneously with blood or plasma transfusions or immune globulin; these products can interfere with development of desired antibodies. Ideally, live-microbial vaccines should be given 2 weeks before or 6 to 12 weeks after the immune globulins.
Live-microbial vaccines include the following:
Polio (oral preparation only; no longer licensed or available in the United States)
Vaccine Safety
In the United States, the safety of vaccines is ensured through two surveillance systems: the CDC's and the U.S. Food and Drug Administration's (FDA) Vaccine Adverse Event Reporting System (VAERS) and the Vaccine Safety Datalink (VSD).
VAERS is a safety program cosponsored by the FDA and the CDC; VAERS collects reports from individual patients who believe that they had an adverse event after a recent vaccination. Health care professionals are also required to report certain events after vaccination and may report events even if they are unsure the events are vaccine-related. VAERS reports originate all across the United States and provide a rapid assessment of potential safety issues. However, VAERS reports can show only temporal associations between vaccination and the suspected adverse event; they do not prove causation. Thus, VAERS reports must be further evaluated using other methods. One such method uses the VSD, which uses data from 11 large health care organizations. The data include vaccine administration (noted in the medical record as part of routine care), as well as subsequent medical history, including adverse events. Unlike VAERS, the VSD includes data from patients who have not received a given vaccine as well as those who have. As a result, the VSD can help distinguish actual adverse events from symptoms and disorders that occurred coincidentally after vaccination and thus determine the actual incidence of adverse events.
Nonetheless, many parents remain concerned about the safety of childhood vaccines and their possible adverse effects (particularly autism). These concerns have led some parents to not allow their children to be given some or all of the recommended vaccines (see Vaccine Hesitancy). As a result, outbreaks of diseases made uncommon by vaccination (eg, measles, pertussis) are becoming more common among unvaccinated children in North America and Europe.
One of the main parental concerns is that vaccines may increase the risk of autism. Reasons cited include
A possible connection between the combination measles-mumps-rubella vaccine and autism (see MMR vaccine and autism)
The possibility that thimerosal might cause autism (thimerosal is a mercury-based preservative used in some vaccines—see Thimerosal and autism)
Use of multiple, simultaneous vaccines, given as recommended
In 1998, a brief report in The Lancet postulated a link between the measles virus in the MMR vaccine and autism. This report received significant media attention worldwide, and many parents began to doubt the safety of the MMR vaccine. However, The Lancet retracted the report because it contained serious scientific flaws; many subsequent, large studies have found no evidence to support an association between use of vaccines and risk of autism (1). The US Institute of Medicine Immunization Safety Review Committee reviewed epidemiologic studies (published and unpublished) to determine whether the measles-mumps-rubella vaccine and vaccines containing thimerosal cause autism and to identify possible biologic mechanisms for such an effect; based on the evidence, this group rejected a causal relationship between these vaccines and autism (2).
Some of the concerns regarding autism and childhood vaccines were regarding vaccine constituents. Thimerosal, a preservative, was the focus of some of these concerns, although the MMR vaccine never contained thimerosal. Currently, virtually every vaccine given to children in the United States is thimerosal-free. Small amounts of thimerosal continue to be used in multidose vials of influenza vaccine and in several vaccines intended for use in adults. For information about vaccines that contain low levels of thimerosal, see the Food and Drug Administration's web site (Thimerosal and Vaccines). Thimerosal is also in many vaccines used in resource-poor countries.
As with any treatment, clinicians should talk to their patients about the relative risks and benefits of recommended vaccines (3). In particular, clinicians must make sure that the parents of their patients are aware of the possible serious effects (including death) of vaccine-preventable childhood diseases such as measles, Hib infection, and pertussis, and clinicians should discuss any concerns parents may have about vaccinating their children. Resources for these discussions include the CDC's Talking with Parents about Vaccines for Infants and Vaccine Resources for Parents.
Vaccine safety references
1. Gerber JS, Offit PA: Vaccines and autism: A tale of shifting hypotheses. Clin Infect Dis 48(4):456-461, 2009. doi: 10.1086/596476
2. Institute of Medicine Immunization Safety Review Committee: Immunization safety review: Vaccines and autism. Washington DC, National Academies Press, 2004.
3. Spencer JP, Trondsen Pawlowski RH, Thomas S: Vaccine adverse events: Separating myth from reality. Am Fam Physician 95(12):786–794, 2017. PMID: 28671426
Immunization for Travelers
Immunizations may be required for travel to areas where infectious diseases are endemic (see table Vaccines for International Travel). The CDC can provide this information; a telephone service (1-800-232-4636 [CDC-INFO]) and web site (Travelers' Health) are available 24 hours/day.
More Information
The following English-language resources may be useful. Please note that THE MANUAL is not responsible for the content of these resources.
Centers for Disease Control and Prevention: Current immunization schedules
Advisory Committee on Immunization Practices (ACIP): Vaccine-Specific Recommendations
ACIP: Recommended Adult Immunization Schedule, United States, 2024
ACIP: General Best Practice Guidelines for Vaccine Administration
Children's Hospital of Philadelphia: Vaccine Education Center
European Centre for Disease Prevention and Control (ECDC): Vaccine schedules in all countries in the EU/EEA
