Overview of Immunization

Vaccines should be given exactly as recommended on the package insert; however, for most vaccines, the interval between a series of doses may be lengthened without losing efficacy.

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) and Administering Vaccines to Adults from the Immunization Action Coalition.

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 Vaccine administration reference 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... read more ).

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 practitioners and institutions to make sure that vaccinations are up to date.

If a vaccine series (eg, for hepatitis B or human papillomavirus) is interrupted, practitioners 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).

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 increases the risk of a serious adverse reaction. A vaccine should not be given when a contraindication is present.

In the US, 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 practitioners 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 country 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 9 large managed care organizations (MCOs) representing more than 9 million people. 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 Effectiveness and Safety of Childhood Vaccination and their possible adverse effects (particularly autism). These concerns, perpetuated on the Internet, have led some parents to not allow their children to be given some or all of the recommended vaccines (see Vaccine Hesitancy 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 Autism Spectrum Disorders . Reasons cited include

In 1998, Andrew Wakefield and colleagues published a brief report in The Lancet (see MMR vaccine and autism Measles-mumps-rubella (MMR) vaccine Despite the rigorous vaccine safety systems in place in the US, some parents remain concerned about the safety of the use and schedule of vaccines in children. These concerns have led some parents... read more ). In it, Wakefield 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, since then, The Lancet has retracted the report because it contained serious scientific flaws; many subsequent, large studies have failed to show any link between the vaccine and autism.

Gerber and Offit reviewed epidemiologic and biologic studies concerning this issue and found no evidence to support an association between use of vaccines and risk of autism ( 1 Vaccine safety references 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... read more ). 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 Vaccine safety references 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... read more ).

At this time, virtually every vaccine given to children in the US is thimerosal-free. Small amounts of thimerosal continue to be used in multidose vials of influenza vaccine and in several other 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 developing countries.

As with any treatment, clinicians should talk to their patients about the relative risks and benefits of recommended vaccines ( 3 Vaccine safety references 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... read more ). 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 Parents' Guide to Childhood Immunizations.

Immunizations may be required for travel to areas where infectious diseases are endemic (see table Vaccines for International Travel 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.

The following are some English-language resources that may be useful. Please note that THE MANUAL is not responsible for the content of these resources.

See the following Centers for Disease Control and Prevention (CDC) sites for comprehensive information about immunization schedules, recommendations for vaccine administration, vaccine resources for travelers, vaccine safety, and vaccine-related patient-friendly resources: