This chapter describes how vaccines licensed for use in the U.S.
are monitored for safety, and presents general information about
the provider's role in immunization safety. For more information
about contraindications and precautions, such as pregnancy and
immunosuppression, refer to the General Recommendations on
Immunization chapter, p. 13, and to Appendix A. Specific information
about adverse events and contraindications for each vaccine
may be found in the appropriate chapters.

THE IMPORTANCE OF VACCINE SAFETY PROGRAMS
Vaccination is among the most significant public health success
stories of all time. However, like any pharmaceutical product, no
vaccine is completely safe or effective. While almost all known vaccine
adverse events are minor and self-limited, some vaccines have
been associated with very rare, but serious health effects. The following
key considerations underscore the need for an active and
ongoing vaccine safety program.

DECREASES IN DISEASE RISKS
Today, vaccine-preventable diseases are at or near record lows. By
virtue of their absence, these diseases are no longer a reminder of
the benefits of vaccination. At the same time, approximately
10,000 cases of adverse events following vaccination are reported
in the U.S. each year (these include both true adverse reactions
and events that coincidentally occur after vaccination). This number
exceeds the current reported incidence of vaccine-preventable
childhood diseases. As a result, parents and providers in the U.S.
are more likely to know someone who has experienced an adverse
event following immunization than they are to know someone who
has experienced a reportable vaccine-preventable disease. Thus,
the success of vaccination has led to increased public attention on
health risks associated with vaccines.

PUBLIC CONFIDENCE
Maintaining public confidence in immunizations is critical for preventing
drops in vaccination rates that can result in outbreaks of
disease. While the majority of parents believe in the benefits of
immunization and have their children vaccinated, some have concerns
about the safety of vaccines. Public concerns about the safety
of whole cell pertussis vaccine in the 1980's resulted in
decreased vaccine coverage levels and the return of epidemic disease
in Japan, Sweden, United Kingdom and several other countries.
In the U.S., similar concerns led to increases both in the
number of lawsuits against manufacturers and the price of vaccines,
and a decrease in the number of manufacturers willing to
produce vaccines. Close monitoring and timely assessment of suspected
vaccine adverse events can distinguish true vaccine reactions
from coincidental unrelated events and help to maintain public
confidence in immunizations.
Vaccine Safety
LOW TOLERANCE FOR VACCINE RISKS
A higher standard of safety is generally expected of vaccines than
of other medical interventions because, in contrast to most pharmaceutical
products which are administered to ill persons for curative
purposes, vaccines are generally given to healthy persons to
prevent disease. Public tolerance of adverse reactions related to
products given to healthy persons, especially healthy infants and
children, is substantially lower than for products administered to
persons who are already sick. This lower risk tolerance for vaccines
translates into a need to investigate the possible causes of very rare
adverse events following vaccinations; a frequency of side effects
that would be acceptable for other pharmaceutical products.

WIDESPREAD AND MANDATED USE OF VACCINES
Vaccines must also meet the highest standards of safety because
almost all children in the U.S. are immunized. Not only do most
parents immunize their children to protect them against vaccinepreventable
diseases, but immunization is also mandated under
many state and local school entry requirements. Because of this
widespread use, safety problems with vaccines have the potential to
impact a large number of people. The importance of ensuring the
safety of a relatively universal human-directed "exposure" like
immunizations is the basis for strict regulatory control of vaccines
in the U.S. by the Food and Drug Administration (FDA).

SOUND IMMUNIZATION RECOMMENDATIONS AND
POLICY
In a context in which risks of contracting vaccine-preventable diseases
are low, the risks of vaccine side effects, especially the very
small chance of serious adverse effects, take on greater weight and
need to be continually reevaluated. Public health recommendations
for vaccine programs and practices represent a dynamic balancing
of risks and benefits. Vaccine safety monitoring is necessary
to accurately weigh this balance and adjust vaccination policy. This
was done, for example, in the U.S. with smallpox and oral polio
vaccines as disease neared global eradication. Complications associated
with each vaccine exceeded the risks of the diseases, leading
to discontinuation of routine smallpox vaccinations in the U.S.
(prior to actual global eradication) and a shift to a safer inactivated
polio vaccine. Sound immunization policies and recommendations
affecting the health of the nation depend upon the ongoing monitoring
of vaccines and continuous assessment of immunization
benefits and risks.

METHODS OF MONITORING VACCINE SAFETY
PRELICENSURE
Vaccines, like other pharmaceutical products, undergo extensive
safety and efficacy evaluations in the laboratory, in animals, and in
sequentially-phased human clinical trials prior to licensure. Phase
I human clinical trials usually involve anywhere from 20 to 100
volunteers and focus on detecting serious side effects. Phase II trials
generally enroll hundreds of volunteers. These trials might take
a few months, or last up to three years. Safety is still an important
focus, but now tests are also charting how the human immune system
responds to the vaccine. At this time, the vaccine is finetuned.
Phase II trials set the most effective use of the vaccine, the
best dose for effectiveness and safety and the right number of
doses. Next, the vaccine moves into phase III trials. Phase III vaccine
trials may last several years. A few hundred to several thousand
volunteers may be involved. Some volunteers receive another
already-licensed vaccine, allowing researchers to compare one vaccine
to another for adverse health effects – anything from a sore
arm to a serious reaction. If the vaccine is shown to be safe and
effective in Phase III, the manufacturer applies for a license from
the FDA. The FDA licenses the vaccine itself (the "product
license") and licenses the manufacturing plant where the vaccine
will be made (the "establishment license"). During the application,
the FDA reviews everything – the clinical trial results, product
labeling, the plant itself, and the manufacturing protocols.
FDA licensure occurs only after the vaccine has met rigorous standards
of efficacy and safety, and when its potential benefits in preventing
disease clearly outweigh its risks. However, while rates of
common vaccine reactions, such as injection site reactions and
fever, can be estimated before licensure, the comparatively small
number of patients enrolled in these trials generally limits detection
of rare side effects or side effects that may occur many months
after the vaccine is given. Even the largest prelicensure trials
(10,000's persons) are inadequate to assess the vaccine's potential
to induce rare side effects. Therefore, it is essential to monitor
reports of vaccine-associated adverse events once the vaccine has
been licensed and released for public use.
Fundamental to preventing safety problems is the assurance that
any vaccines for public use are made using Good Manufacturing
Practices (GMP) with prerelease lot testing for purity and potency.
Manufacturers must submit samples of each vaccine lot and results
of their own tests for potency and purity to the FDA before releasing
them.

POSTLICENSURE
Because rare reactions, delayed reactions, or reactions within subpopulations
may not be detected before vaccines are licensed,
postlicensure evaluation of vaccine safety is critical. The objectives
of postlicensure surveillance are to:
• identify rare reactions not detected during prelicensure studies
• monitor increases in known reactions
• identify risk factors or pre-existing conditions that may promote
reactions
• identify whether there are particular vaccine lots with unusually
high rates or types of events
• identify signals of possible adverse reactions which may warrant
further study or effect current immunization recommendations.
Historically, postlicensure monitoring of vaccine safety has relied
on healthcare providers and the public to report side effects and
"ad hoc" research studies to investigate possible rare associations
between vaccines and identified health conditions of interest to scientists.
Today, Phase IV trials and large-linked databases (LLDB)'s
have been added to improve our capabilities to study rare risks of
specific immunizations. Phase IV studies can be an FDA requirement
for licensure. These trials include volunteers in the 10,000s
and may address questions of long-term effectiveness and safety or
examine unanswered questions identified in Phase III clinical trials.
Most recently, a clinical evaluation network has been established
which will increase our understanding of vaccine reactions at the
individual, "patient" level.

THE VACCINE ADVERSE EVENT REPORTING SYSTEM
(VAERS)
The National Childhood Vaccine Injury Act of 1986, mandated
that healthcare workers who administer vaccines, and licensed vaccine
manufactures, report certain adverse health events following
specific vaccinations. The Vaccine Adverse Event Reporting
System (VAERS) is a national reporting system, jointly administered
by the CDC and FDA.VAERS was created in 1990 to unify
efforts for the collection of all reports of clinically significant
adverse events.VAERS is a passive reporting system and accepts
reports from health professionals, vaccine manufacturers, and the
general public. Reports are submitted via mail and fax as well as
the internet. All reports, whether submitted directly to VAERS or
via state or local public health authorities or manufacturers, are
coded and entered into the VAERS database. VAERS receives
about 10,000 reports per year (>130,000 total to date). Though
this seems like a very large number, it is relatively small compared
with the approximately 100 million doses of childhood vaccines
distributed during the past decade, as well as millions of additional
doses given to adults.
VAERS seeks to capture all clinically significant medical events
occurring postvaccination, even if the reporter is not certain that
the incident is vaccine-related. In a review of VAERS from 1991-
2001, reports are received from manufacturers (36.2%); health
care providers (20%); state and local health departments (27.6%);
patients or parents (4.2%); others (7.3%) and unknown (4.7%).
Data collected on the VAERS reporting form include information
about the patient, the vaccination(s) given, the reported health
effect, called an adverse event, and the person reporting the event.
According to FDA regulations, serious reports are defined as those
involving hospitalization or prolongation of hospitalization, death,
or reported life-threatening illness or permanent disability. All
reports classified as serious are followed-up to obtain additional
medical information in order to provide as full a picture of the case
as possible. For serious reports, letters to obtain information about
recovery status are mailed to the reporters at 60 days and 1 year
after vaccination. All records submitted to VAERS directly or as
part of follow-up activities are protected by strict confidentiality
requirements.
Despite some limitations,VAERS has been able to fulfill its primary
purpose of detecting new and/or rare vaccine adverse events,
increases in rates of known side effects, and patient risk factors for
particular types of adverse events. Examples include tracking and
raising the concern about intussusception after rotavirus vaccine
and anaphylactic reaction to MMR vaccine caused by gelatin allergy.
Additional studies are always required to confirm "signals"
detected by VAERS (because not all events are causally related to
vaccine), but the system remains the cornerstone of postlicensure
safety surveillance efforts. More information about VAERS, including
the ability to report online can be obtained from the VAERS
website at http://www.vaers.org or by calling the VAERS information
line at 800-822-7967.
VAERS data with personal identifiers removed are available on the
world wide web at http://www. vaers.org at no cost or through the
National Technical Information Service at http://www.ntis.gov or
by phone at 800-553-6847 for a fee.

ADVERSE EVENT CLASSIFICATIONS AND ASSESSMENT OF
CAUSALITY
Adverse events following vaccination can be classified by frequency
(common, rare), extent (local, systemic), severity (hospitalization,
disability, death), causality, and preventability (intrinsic to vaccine,
faulty production, faulty administration). A recent classification
divides vaccine adverse events as follows:
• Vaccine-induced: due to the intrinsic characteristic of the vac
cine preparation and the individual response of the vaccinee,
these events would not have occurred without vaccination (e.g.,
vaccine-associated paralytic poliomyelitis).
• Vaccine-potentiated: the event would have occurred anyway,
but was precipitated by the vaccination (e.g., first febrile seizure
in a predisposed child).
• Programmatic error: due to technical errors in vaccine storage,
preparation, handling, or administration.
• Coincidental: the reported event was not caused by vaccination
but happened by chance occurrence or due to underlying illness.
It is natural for some people to suspect vaccine to be the cause
when a health problem occurs following vaccination, but in reality
a causal association may or may not exist. Simply because a health
problem occurred after vaccination does not mean that vaccination
caused the health problem; more information is needed to establish
a causal relationship. An adverse health event can be causally
attributed to vaccine more readily if: 1) the health problem occurs
during a plausible time period following vaccination, 2) the adverse
event corresponds to those previously associated with a particular
vaccine, 3) the event conforms to a specific clinical syndrome
whose association with vaccination has strong biologic plausibility
(e.g., anaphylaxis) or occurs following the natural disease, 4) a laboratory
result confirms the association (e.g., isolation of vaccine
strain varicella vaccine from skin lesions of a patient with rash), 5)
the event recurs on re-administration of the vaccine ("positive
rechallenge"), 6) a controlled clinical trial or epidemiologic study
shows greater risk of a specific adverse event among vaccinated vs.
unvaccinated (control) groups, and 7) a finding linking an adverse
event to vaccine has been confirmed by other studies.

LARGE-LINKED DATABASES (LLDB)
Historically, when a signal of a potential vaccine safety concern
was generated from passive surveillance, further ad hoc studies
were needed to test the hypothesis. Such studies, while potentially
informative about vaccine causality, were costly, time-consuming,
and usually limited to assessment of a single event. The need to
improve postlicensure monitoring of drug safety became widely
recognized following the thalidomide incident. Faced with the
inability of passive surveillance systems to establish causal relationships,
and the lack of timeliness of ad hoc studies, pharmacoepidemiologists
during the 1980s began to turn to large databases
linking computerized pharmacy prescription (and later, immunization
records) and computerized medical records. These LLDBs are
derived from defined populations such as members of health maintenance
organizations (HMOs), single-provider healthcare systems,
and Medicaid programs. As these databases are usually generated
in the routine administration of such programs and do not require
completion of a vaccine adverse event reporting form, the problems
of under-reporting or recall bias are reduced. Therefore,
LLDBs can potentially provide an economical and rapid means of
conducting postlicensure studies of safety of drugs and vaccines.
CDC's Vaccine Safety Datalink (VSD) project is one example of
such a system. It links the immunization and medical records on
members of 8 HMOs, totalling >2.5% of the US population for
various vaccine safety studies. For more information about Large
link databases go to http://www.cdc.gov/nip/vacsafe.

CLINICAL IMMUNIZATION SAFETY ASSESSMENT (CISA)
NETWORK
The most recent addition to the postlicensure vaccine safety monitoring
system is the Clinical Immunization Safety Assessment
(CISA) Network, which is designed to improve scientific understanding
of vaccine safety issues at the individual, "patient" level.
The CISA network will closely evaluate individuals who have experienced
select adverse health events following vaccination.The
results of these evaluations will be used to gain a better understanding
of how such events might occur, and to develop protocols
or guidelines for healthcare providers to help them manage similar
situations. In addition, the CISA centers will serve as regional
information sources to which clinical vaccine safety questions can
be referred. Prior to the creation of the CISA network, no coordinated
facilities existed in the US that investigated and managed
vaccine side effects on an individual level for the purposes of providing
patient care and systematically collecting and evaluating the
experiences.
Established in 2001, the CISA network consist of 7 centers of
excellence with vaccine safety expertise in partnership with CDC.
These centers include Johns Hopkins University and the University
of Maryland, in Baltimore, MD; Boston University Medical Center
in Boston, MA; Columbia Presbyterian Hospital in New York City,
NY;Vanderbilt University in Nashville,TN; Northern California
Kaiser in Oakland and Stanford University in Palo Alto, CA. For
more information about CISA visit http://www.vaccinesafety.net.

VACCINE INJURY COMPENSATION
The topic of vaccine safety was prominent during the mid 1970s
with increases in lawsuits filed on behalf of those presumably
injured by the whole-cell pertussis vaccine (DPT). Legal decisions
were made and damages awarded despite the lack of scientific evidence
to support vaccine injury claims. As a result of the liability,
prices soared and several manufacturers halted vaccine production.
A vaccine shortage resulted and public health officials became concerned
about the return of epidemic disease. In order to reduce liability
and respond to public health concerns, Congress passed the
National Childhood Vaccine Injury Act (NCVIA) in 1986.
As a result of the NCVIA, the National Vaccine Injury
Compensation Program (VICP) was established. This program is
intended to compensate individuals who experience certain health
events following vaccination on a "no fault" basis. "No fault" means
that people filing claims are not required to prove negligence on
the part of either the healthcare provider or manufacturer to
receive compensation. The program covers all routinely recommended
childhood vaccinations. Settlements are based on a
Vaccine Injury Table which summarizes the adverse events associated
with vaccines.This table was developed by a panel of experts
who reviewed the medical literature and identified the serious
adverse events that are reasonably certain to be caused by vaccines.
The Vaccine Injury Table was created to justly compensate those
possibly injured by vaccines while separating out unrelated claims.
As more information becomes available from research on vaccine
side effects, the Vaccine Injury Table is amended. The Vaccine
Injury Table can be found in Appendix F.
The VICP has received more than 5,000 claims since its effective
date of October 1, 1988, 85 percent of which are for vaccines
administered prior to the effective date (retrospective claims).
VICP has achieved its policy goals of providing compensation to
those injured by rare adverse events and liability protection for vaccine
manufacturers and administrators. For more information
about the VICP, visit their website at
http://www.hrsa.gov/osp/vicp/vicp.html.

THE IMMUNIZATION PROVIDER'S ROLE
Federal regulations require vaccines to undergo years of testing
before they can be licensed. Once in use, vaccines are monitored
continually for safety and efficacy. Immunization providers also
play a key role in helping to ensure the safety and efficacy of vaccines
through proper vaccine storage and administration, timing
and spacing of vaccine doses, observation of precautions and contraindications,
management of vaccine side effects, reporting of
suspected side effects to VAERS, and patient/parent education
about vaccine benefits and risks.

VACCINE STORAGE AND ADMINISTRATION
In order to achieve the best possible results from vaccines, immunization
providers should carefully follow the recommendations for
storage, handling, and administration found in each vaccine's package
insert. Other steps to help ensure vaccine safety include: 1)
inspecting vaccines upon delivery and monitoring refrigerator and
freezer temperatures to assure maintenance of the cold chain, 2)
rotating vaccine stock so the oldest vaccines are used first, 3) never
administering a vaccine later than the expiration date, 4) administering
vaccines within the prescribed time periods following reconstitution,
5) waiting to draw vaccines into syringes until immediately
prior to administration, 6) never mixing vaccines in the same
syringe unless they are specifically approved for mixing by the
FDA, and 7) recording vaccine and administration information,
including lot numbers and injection sites, in the patient's record. If
errors in vaccine storage and administration occur, corrective
action should be taken immediately to prevent them from happening
again and public health authorities should be notified. See
Appendix D for more information on vaccine storage and handling.

TIMING AND SPACING
The timing and spacing of vaccine doses are two of the most
important issues in the appropriate use of vaccines. To ensure
optimal results from each immunization, providers should follow
the currently recommended immunization schedules for children,
adolescents, and adults. Decreasing the timing intervals between
doses of the same vaccine may interfere with the vaccines antibody
response. For more specific information on timing and spacing of
vaccines see chapter 2. A table on recommended minimum ages
and intervals between vaccine doses can be found in appendix A.
Providers should also remember:
• Administering all needed vaccines during the same visit is important
because it increases the likelihood that children will be fully
immunized as recommended. Studies have shown that vaccines
are as effective when administered simultaneously as they are
individually and carry no greater risk for adverse reactions. Such
reactions are thought to result from the formation of antigenantibody
complexes.
• There is no medical basis for giving combination vaccines, such
as MMR, separately. Administration of separated combination
vaccines results in more discomfort and higher risk of disease
from delayed protection.
• Some vaccines, like pediatric diphtheria and tetanus, produce
increased rates of side effects when given too frequently. Good
record keeping, maintaining careful patient histories, and adherence
to recommended schedules can decrease the chances that
patients receive extra doses of vaccines.

CONTRAINDICATIONS AND PRECAUTIONS
Contraindications and precautions to vaccination indicate when
vaccines should not be given. A contraindication is a condition in
a patient that increases the chance of a serious, adverse reaction.
In general, a vaccine should not be administered when a contraindication
is present. A precaution is a condition in a patient
that may increase the chance of a serious side effect or compromise
the ability of the vaccine to produce immunity. Normally, vaccination
is deferred when a precaution is present. However, situations
may arise when the benefits of vaccination outweigh the risk of a
side effect, and the provider may decide to vaccinate the patient.
Most contraindications and precautions are temporary and the
vaccine may be given at a later time. The CDC Guide to
Contraindications to Childhood Vaccinations summarizes current
recommendations in a handy booklet. It can be ordered on-line at
http://www.cdc.gov/nip. More information about contraindications
can be found in the contraindications/precautions table in appendix
A and in Advisory Committee on Immunization Practices
(ACIP) Statements for individual vaccines. Recommendations for
immunizing persons who are immunocompromised can be found
in appendix A. Information on allergic reactions to vaccines can be
found in the American Academy of Pediatrics Red Book.
Screening for contraindications and precautions is key to preventing
serious adverse reactions to vaccines. Every provider who
administers vaccines should screen every patient before giving a
vaccine dose. Sample screening questionnaires can be found in
Appendix A. Many conditions are often inappropriately regarded
as contraindications to vaccination. For example, in most cases,
the following are not considered contraindications:
• Mild acute illness (e.g., diarrhea and minor upper-respiratory
tract illnesses, including otitis media) with or without low-grade
fever
• Mild to moderate local reactions and/or low-grade or moderate
fever following a prior dose of the vaccine
• Current antimicrobial therapy
• Convalescent phase of illness
• Recent exposure to infectious disease
• Premature birth
• Breastfeeding

MANAGING VACCINE SIDE EFFECTS
Providers should use their best clinical judgment on specific management
of suspected vaccine side effects. Allergic reactions to
vaccines are estimated to occur after vaccination of children and
adolescents at a rate of 1 case for every 1.5 million doses of vaccine.
Any provider who administers vaccines should have procedures
in place and be prepared for emergency care of a person who
experience an anaphylactic reaction. Any provider who administers
vaccines should have procedures in place for the emergency care of
a person who experiences an anaphylactic reaction. Epinephrine
and equipment for maintaining an airway should be available for
immediate use. All vaccine providers should be familiar with the
office emergency plan, and should be certified in cardiopulmonary
resuscitation.

REPORTING SUSPECTED SIDE EFFECTS TO VAERS
Healthcare providers are encouraged to report suspected vaccine
reactions to VAERS through their website at http://www.vaers.org
or by calling the VAERS information line at 1-800-822-7967.
When providers report suspected vaccine reactions to VAERS, they
provide valuable information that is needed for the ongoing evaluation
of vaccine safety. The CDC and FDA use VAERS information
to ensure the safest strategies of vaccine use and to further reduce
the rare risks associated with vaccines.

BENEFIT AND RISK COMMUNICATION
Parents, guardians, legal representatives, and adolescent and adult
patients should be informed of the benefits and risks of vaccines in
understandable language. Opportunity for questions should be
provided before each vaccination. Discussion of the benefits and
risks of vaccination is sound medical practice and is required by
law.
The National Childhood Vaccine Injury Act requires that vaccine
information materials be developed for each vaccine covered by the
Act. These materials, known as Vaccine Information Statements, must
be provided by all public and private vaccination providers before
each dose of vaccine. Copies of Vaccine Information Statements
are available from state health authorities responsible for immunization,
or they can be obtained from CDC's National
Immunization Program website at http://www.cdc.gov/nip.
Translations of Vaccine Information Statements into languages
other than English are available from certain state immunization
programs and from the Immunization Action Coalition website at
http://www.immunize.org.
Healthcare providers should anticipate that some parents or
patients may have questions regarding the need for or safety of vaccination.
A few may refuse certain vaccines, or even reject all vaccinations.
Some persons might have religious or personal objections
to vaccinations. Having a basic understanding of how
patients view vaccine risk and developing effective approaches in
dealing with vaccine safety concerns when they arise is imperative
for vaccination providers.
Each person understands and reacts to vaccine information on the
basis of different factors, including prior experience, education,
personal values, method of data presentation, perceptions of the
risk for disease, perceived ability to control those risks, and their
risk preference. Some people may also be exposed to inaccurate
information about vaccine risks through the media and Internet
sites. Healthcare professionals can help by assessing patient's specific
concerns and information needs, providing them with accurate
information, and referring them to credible sources for more
information.
When a parent or patient initiates discussion regarding a vaccine
concern, the healthcare professional should discuss the specific
concerns and provide factual information, using language that is
appropriate. Effective, empathetic vaccine risk communication is
essential in responding to misinformation and concerns. The
Vaccine Information Statements provide an outline for discussing
vaccine benefits and risk. Fact sheets, titled,Vaccines a safe choice
and Helping Parents who question vaccines (available from the
NIP website) may also be helpful.
Although a limited number of providers might choose to exclude
from their practice those patients who question or refuse vaccination,
the more effective public health strategy is to identify common
ground and discuss measures that need to be followed if the
patient's decision is to defer vaccination. Healthcare providers can
reinforce key points regarding each vaccine, including safety, and
emphasize risks encountered by unimmunized children. Parents
should be advised of state laws pertaining to school or child care
entry, which might require that unimmunized children stay home
from school during outbreaks. Documentation of these discussions
in the patient's record, including the refusal to receive certain vaccines
(i.e., informed refusal), might reduce any potential liability if
a vaccine-preventable disease occurs in the unimmunized patient.
Vaccine Safety
CONCLUSION
Many factors contribute to the need for an active and ongoing vaccine
safety program. Vaccines undergo extensive safety and efficacy
evaluations in the laboratory, in animals, and in human clinical trials
prior to licensure. Because rare reactions, delayed reactions, or
reactions within sub-populations may not be detected before vaccines
are licensed, postlicensure evaluation is critical. Providers
also play and important role in helping to ensure vaccine safety
and should discuss the benefits and risks of vaccination with parents,
guardians, legal representatives, and adolescent and adult
patients. More information about the topics discussed in this
chapter can be obtained at http://www.cdc.gov/nip, and a list of
vaccine safety resources has been included in Appendix F.

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CDC. National Childhood Vaccine Injury Act: Requirements for
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CDC. Surveillance for safety after immunization. MMWR 2003;52
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