**[Influenza Glossary]{.underline}**

**A**

**Adjuvant:** A substance added during production of a vaccine to
strengthen the body's immune response to that vaccine.

**Amantadine:** One of 4 prescription medications (along with
rimantadine, oseltamivir, and zanamivir) with antiviral activity against
influenza viruses licensed by the U.S. Food and Drug Administration for
the treatment and/or prevention of influenza. Controlled clinical trials
have demonstrated the efficacy of all four antiviral medications in
reducing symptom duration when used for treatment of influenza
infections. However, all the drugs may not always work against different
influenza virus strains because these can become resistant to one or
more of these medicines. For example, analyses have shown that some of
the H5N1 viruses isolated from poultry and humans in Southeast Asia are
resistant to amantadine and rimantadine.

**Animal culling:** Selective slaughter and removal of animals from a
population to reduce the potential spread of disease. Culling of poultry
populations has been used to minimize the potential spread of avian
influenza.

**Animal reservoir:** When an animal species is naturally infected by a
pathogen and acts as a host for that pathogen it is said to be an animal
reservoir for that pathogen. For example, avian influenza viruses
circulate among birds worldwide. Certain birds, particularly water
birds, act as hosts for influenza viruses by carrying the virus in their
intestines and shedding it. These viruses sometimes can "jump" to other
species. Changes in the virus's gene structure then may occur,
increasing the potential for infection of other species and pandemic
influenza. (Also see Antigenic Drift and Antigenic Shift).

**Animal-to-Human Transmission:** An infected animal transmits illness
to a human. In influenza, animal influenza viruses may be transmitted
from birds to humans directly from birds or from contact with surfaces
contaminated with avian influenza virus.

**Antigenic Drift:** Influenza viruses can undergo antigenic change in
two ways: antigenic drift and antigenic shift. Antigenic drift refers to
small, gradual changes that occur through point mutations in the two
genes that contain the genetic material to produce the main surface
proteins, hemagglutinin, and neuraminidase. These point mutations occur
unpredictably and result in minor changes to these surface proteins.
Antigenic drift produces new virus strains that may not be recognized by
antibodies to earlier influenza strains. This process works as follows:
a person infected with a particular influenza virus strain develops
antibody against that strain. As newer virus strains appear, the
antibodies against the older strains might not recognize the \"newer\"
virus, and infection with a new strain can occur. In most years, one or
two of the three virus strains in the influenza vaccine are updated to
keep up with the changes in the circulating influenza viruses. For this
reason, people who want to be immunized against influenza need to be
vaccinated every year.

**Antigentic Shift:** Influenza viruses can undergo antigenic change in
two ways: antigenic drift and antigenic shift. Antigenic shift refers to
an abrupt, major change to produce a novel influenza A virus subtype in
humans that was not currently circulating among people. Antigenic shift
can occur either through direct animal (poultry)-to-human transmission
or through mixing of human influenza A and animal influenza A virus
genes to create a new human influenza A subtype virus through a process
called genetic reassortment.

**Antiviral:** Any medicine capable of destroying or weakening a virus.

**Antiviral agents for influenza:** Four different prescription
influenza antiviral medications (amantadine, rimantadine, oseltamivir,
and zanamivir) are approved by the U.S. Food and Drug Administration
(FDA) for the treatment and/or prophylaxis of influenza. All four have
activity against influenza A viruses. Controlled clinical trials have
demonstrated the efficacy of all four antiviral medications in reducing
symptom duration when used for treatment of influenza infections.
However, all the drugs may not always work against different influenza
virus strains because these can become resistant to one or more of these
medicines. For example, analyses have shown that some H5N1 viruses
isolated from poultry and humans in Southeast Asia are resistant to
amantadine and rimantadine.

**Antiviral resistance:** Influenza virus strains can become resistant
to one or more of the antiviral agents for influenza making these drugs
ineffective against that strain of the virus.

**Antiviral therapy:** The use of antiviral medications to treat
disease.

**Asymptomatic infection:** An infection that exists without any
apparent disease symptoms. Influenza infection can be asymptomatic.

**Attenuate:** To weaken, thin, or reduce in strength or value. (Also
see Live Attenuated Influenza Vaccine).

**Attenuated vaccine:** A vaccine that consists of live virus that has
been weakened through chemical or physical processes to produce an
immune response without causing severe effects of the disease. (Also see
Live Attenuated Influenza Vaccine).

**Avian influenza:** Influenza A viruses that are naturally occurring in
wild birds. Infected birds serve as natural hosts from which some
influenza viruses or genes can be transmitted into other animal or human
populations. Avian influenza viruses do not usually infect humans;
however, confirmed cases of human infection from several subtypes of
avian influenza infection have been reported since 1997. Currently,
outbreaks of avian influenza A (H5N1) among birds have resulted in human
cases in Asia and Europe.

**B**

**Biosafety Level (BSL):** Specific combinations of work practices,
safety equipment, and facilities designed to minimize the exposure of
workers and the environment to infectious agents. BSL-1 applies to
agents that do not ordinarily cause human disease. BSL-2 is appropriate
for agents that can cause human disease but have limited potential for
transmission. BSL-3 applies to agents that can cause serious infection
and may be transmitted by the respiratory route. BSL-4 is used when
diagnosing or working with agents that pose a high risk of
life-threatening disease, may be transmitted by the aerosol route, and
for which there is no vaccine or therapy.

**C**

**Chemoprophylaxis:** The prevention of disease using medications.

**Complications from influenza:**

-   Common complications include secondary bacterial pneumonia and
    worsening of chronic underlying health conditions. In children,
    inflammation of the ear is a common complication from influenza.

-   Uncommon complications from influenza include inflammation of
    voluntary muscles and heart muscles, toxic-shock syndrome and Reye
    syndrome (usually associated with the use of aspirin and other
    salicylate medications in children and adolescents).

**Conjunctivitis:** Inflammation of the membrane that lines the inner
surface of the eyelid and the exposed surface of the eyeball.
Conjunctivitis is one symptom sometimes associated with avian influenza
A infection in humans. For example, conjunctivitis was reported in the
majority of human cases of avian influenza A (H7N7) infection during an
outbreak in the Netherlands in 2003.

**Containment measures:** Measures taken to contain disease outbreak,
including isolation, surveillance, and quarantine. In the context of an
emerging influenza pandemic, because of the relatively brief incubation
period of influenza, containment measures may be helpful early on.
Containment measures may include discouraging or banning large indoor
gatherings, closing schools, isolating persons with confirmed or
suspected influenza and quarantine of persons exposed to suspected or
confirmed cases.

**Cough etiquette:** Terminology used to describe a series of steps to
help prevent droplet transmission of respiratory illnesses such as
influenza. Cough etiquette includes:

-   Using a tissue to cover your mouth and nose when you cough or sneeze

-   Washing hands frequently with soap and water (Also see respiratory
    hygiene).

**Crisis and Emergency Risk Communication:** This encompasses the
urgency of disaster communication with the need to communicate risks and
benefits to stakeholders and the public. Crisis and emergency risk
communication is the effort by experts to provide information to allow
an individual, stakeholder, or entire community to make the best
possible decisions about their well-being within nearly impossible time
constraints and to help people accept the imperfect nature of choices
during a crisis.

**Crisis Communication:** Communications about a crisis for stakeholders
and the public. The crisis is an unexpected event that is out of the
control of the involved organization.

**D**

**Direct Patient Care:** Hands-on or face-to-face contact with patients.
Staff involved in direct care of influenza patients includes doctors,
nurses, and other health-care workers who care for patients, as well as
staff such as paramedics and triage receptionists who are physically
located in emergency rooms, clinics, or other places where they have
frequent face-to-face contact with patients. It also might include
police or other persons, such as volunteers, who routinely work in
health-care settings and have hands-on or face-to-face contact with
patients. "Direct patient care" does not include staff working primarily
in office settings where patients are not present, even if the office is
located in a hospital or clinic. Special infection control measures may
be needed for personnel involved in direct patient care.

**Droplet Transmission:** Disease transmission that occurs primarily
through respiratory droplets. Influenza is spread from person to person
mainly by inhalation or contact with respiratory droplets. Droplets may
be produced by coughing or sneezing. They only travel a short distance
(about three feet) and remain suspended in the air for a brief time.

**E**

**Embryonated Chicken Eggs:** Fertile chicken eggs used for vaccine
production.

**Endemic:** A disease or infection that is present in a particular
locality, region or people at all times. Avian influenza is considered
endemic in wild birds.

**Enzootic:** A disease that is constantly present in an animal
community but occurs only in small numbers of cases.

**Epidemic:** The occurrence of disease within a specific geographical
area or population that is in excess of what is normally expected.

**Epidemiology:** The study of the distribution and determinants of
health-related states or events in specified populations, and the
application of this study to the control of health problems.

**Epizootic:** An outbreak or epidemic of disease in animal populations.

**Etiology:** The cause or origin of a disease or disorder; the study of
the factors that cause disease, and of the method of their introduction
into the host.

**F**

**FluSurge:** A spreadsheet-based model that provides hospital
administrators and public health officials with estimates of the surge
in demand for hospital-based services during an influenza pandemic.
FluSurge estimates the number of hospitalizations and deaths of an
influenza pandemic and compares the number of persons hospitalized, the
number of persons requiring intensive care unit care, and the number of
persons requiring ventilator support during a pandemic with existing
hospital capacity.

**G**

**H**

**Hemagglutinin (HA):** A type of protein on the surface of influenza
viruses. Influenza type A viruses are divided into subtypes on the basis
of two proteins on the surface of the virus: hemagglutinin (HA) and
neuraminidase (NA).

**"High risk" population:** Those individuals at greatest risk of
developing serious or deadly disease. In the case of seasonal influenza,
this includes the very young and the very old, people living in group
homes, people with underlying heart or lung disease, and people with
weakened immune systems. It is not known who would be at highest risk
from the next pandemic influenza virus that emerges.

**Highly pathogenic avian influenza (HPAI):** Avian influenza A H5 and
H7 viruses can be distinguished as "low pathogenic" and "high
pathogenic" forms on the basis of genetic features of the virus and the
severity of the illness they cause in poultry. A highly pathogenic avian
influenza virus can cause severe illness and high mortality in poultry,
however some HPAI viruses have been found to cause no illness in some
poultry, such as ducks.

**Human-to-Human Transmission:** In efficient human-to-human
transmission the virus is contagious among humans and therefore spreads
easily. In sustained human-to-human transmission, the spread of virus is
ongoing and expanding in the community. To date, human infections with
avian influenza A viruses detected since 1997 have not resulted in
sustained human-to-human transmission. In widespread human-to-human
transmission there are many clusters of H5N1 infection among people that
do not have poultry exposure.

**I**

**Immunization:** The process or procedure by which a person, animal, or
plant is rendered resistant to a specific disease. This term is often
used interchangeably with vaccination or inoculation, although the act
of inoculation does not always result in immunity.

**Immunosuppression:** When the immune system is unable to protect the
body from disease. This condition can be caused by disease (like HIV
infection or cancer) or by certain drugs (like those used in
chemotherapy). Individuals whose immune systems are compromised should
not receive live, attenuated vaccines.

**Inactive vaccine:** A vaccine made from viruses or bacteria that have
been killed through physical or chemical processes. These killed
organisms cannot cause disease.

**Incubation period:** The interval of time between infection by a
microorganism and the onset of illness or the first symptoms of the
illness. The time from when a person is exposed to the seasonal flu
virus to when symptoms begin is about one to four days, with an average
of about two days.

**Influenza (flu)**: A contagious respiratory illness caused by
influenza viruses. It can result in mild to severe illness, and at times
can lead to death. Most healthy people recover from seasonal flu without
complications, but some people, such as older people, young children,
and people with certain health conditions, are at high risk for serious
complications. Symptoms of seasonal influenza include fever, headache,
tiredness, cough, sore throat, runny or stuffy nose, body aches, and
sometimes diarrhea and vomiting.

**Influenza contagion/spread:** Most healthy adults may be able to
infect others with regular human influenza beginning 1 day before
symptoms develop and up to 5 days after becoming sick. That means that
you can pass on the flu to someone else before you know you are sick, as
well as while you are sick. This period may last longer in children.
Influenza virus usually is spread by large respiratory droplets
containing influenza viruses that are produced by coughing and sneezing.

**Influenza-Like-Illnesses (ILI):** A nonspecific respiratory illness
characterized by fever, fatigue, cough, and other symptoms. Most ILI
cases are caused by viruses other than influenza.

**Influenza pandemics**: A global outbreak of influenza that occurs when
a new influenza A virus appears or "emerges" in the human population,
causes serious illness, and then spreads easily from person to person
worldwide. Influenza pandemics have resulted in high rates of illness
and death, social disruption, and economic loss. They occur infrequently
and at irregular intervals. Three pandemics took place in the 20^th^
century: The 1918-1919 "Spanish Flu" pandemic, which was caused by a
Type A (H1N1) virus resulted in more than 500,000 deaths in the U.S. and
more than 20 million deaths worldwide. This was followed by the 1957-58
"Asian Flu" pandemic caused by a Type A (H2N2) virus that killed about
70,000 people in the United States. The 1968-69 "Hong Kong Flu" pandemic
was caused by a Type A (H3N2) virus and killed about 34,000 people in
the U.S. All of these pandemics spread throughout the world within one
year of their detection.

**Influenza type A viruses:** There are three types of influenza
viruses: A, B, and C. Only influenza A viruses are further classified by
subtype on the basis of the two main surface glycoproteins hemagglutinin
(HA) and neuraminidase (NA). Influenza A subtypes and B viruses are
further classified by strains. So far, scientists have discovered 16 HA
subtypes and 9 NA subtypes. However, in the 20^th^ century, only three
subtypes circulated widely in humans: A(H1N1), A(H2N2), and A(H3N2).
Influenza A viruses also can infect a number of animal species including
pigs, birds, horses, seals and whales.

**Influenza vaccine**: A vaccine designed to prevent or lessen the
severity of influenza disease. Annual vaccination is the main method
used to reduce the impact of seasonal influenza. The vaccine is made
from inactivated (killed) influenza virus that prompts an antibody
response promoting immunity from the influenza virus used in the
vaccine. It takes two weeks for the body to develop protective antibody
after vaccination.

**Influenza viruses**: There are three types of influenza viruses: A, B,
and C. Types A and B cause epidemics of respiratory illness in the
United States each winter. Type A viruses historically have been the
ones responsible for influenza pandemics. Type C is milder and has not
caused epidemics. An important characteristic of influenza viruses is
their ability to change so that new viral strains can emerge.

**Inter-pandemic period:** The period between emergence of subtypes.

**Intradermal Administration:** Intradermal administration or
vaccination refers to the injection of vaccine into the skin instead of
the muscle.

**Intramuscular Administration:** Intramuscular administration or
vaccination means the vaccine is injected into the muscle (usually the
arm). Inactivated influenza vaccine is currently administered
intramuscularly.

**Investigational new drug (IND):** Legal provisions that allow for
emergency distribution of unlicensed vaccines, using strict inventory
control and recordkeeping, along with completion of a signed consent
form.

**Isolation:** Isolation is a strategy used by public health authorities
to contain the spread of a contagious illness. Isolation is the
separation of people who are sick with a specific illness from healthy
people and the restriction of their movement to stop the spread of that
illness.

**J**

**K**

**L**

**Low Pathogenic Avian Influenza (LPAI):** Avian influenza A virus
strains are classified as low pathogenic (LPAI) or highly pathogenic
(HPAI) on the basis of specific molecular genetic and pathogenesis
criteria that require specific testing. Most avian influenza A viruses
are LPAI viruses that are usually associated with mild disease in
poultry. LPAI viruses have the potential to evolve into HPAI viruses and
this has been documented in some poultry outbreaks.

**Laboratory Response Network (LRN):** LRN and its partners maintain an
integrated national and international network of laboratories that are
equipped to respond quickly to acts of chemical or biological terrorism,
emerging infectious diseases, and other public health threats and
emergencies. See [www.bt.cdc.gov/lrn/](http://www.bt.cdc.gov/lrn/).

**Live attenuated vaccine:** A vaccine in which live virus is weakened
through chemical or physical processes in order to produce an immune
response without causing the severe effects of a disease.

**Long-term care facility (LTCF):** A facility that provides
rehabilitative, restorative, and/or ongoing skilled nursing care to
patients or residents in need of assistance with activities of daily
living. Long-term care facilities include nursing homes, rehabilitation
facilities, inpatient behavioral health facilities, and long-term
chronic care hospitals.

**M**

**Mechanical ventilation:** Use of equipment by medical staff to assist
patients who need assistance breathing due to complications during
influenza or other illness or disease.

**Monovalent inactivated vaccine:** A vaccine that contains a single
killed virus strain. In the event of a pandemic, it is likely that a
monovalent rather than a trivalent vaccine would be developed to fight
the particular virus responsible for the pandemic.

**N**

**National Pandemic Influenza Preparedness Plan:** A planning document
developed by the National Vaccine Program Office of the Department of
Health and Human Services designed to:

-   Define and recommend preparedness activities before a pandemic.

-   Describe interventions to be implemented for an effective response
    to a pandemic.

-   Guide health departments and the health care system to develop state
    and local pandemic preparedness and response plans.

-   Provide technical information on which to base preparedness and
    response.

The first national pandemic influenza plan was developed in 1978.. The
most recent plan was developed in 2005. The plan is found at
<http://www.hhs.gov/pandemicflu/plan/>

**Neuraminidase (NA):** A type of protein on the surface of the
influenza virus. Influenza type A viruses are divided into subtypes and
named on the basis of two proteins on the surface of the virus:
hemagglutinin (HA) and neuraminidase (NA).

**Neuraminidase inhibitors:** A class of drugs that inhibits influenza A
and B viruses. Oseltamivir and Zanamivir are the two neuraminidase
inhibitors approved by the Food and Drug Administration. (Also see
Oseltamivir and Zanamivir).

**Nosocomial:** An infection occurring in a patient that is acquired at
a hospital or other health care facility. 

**Novel influenza virus:** A viral subtype that has never circulated in
humans, or has not circulated in humans for at least several decades and
to which the large majority of the human population therefore lack
immunity.

**O**

**Orthomyxovirida**e: A family of viruses that includes the viruses
which cause influenza.

**Oseltamivir:** One of 4 prescription medications (along with
amantadine, rimantadine, and zanamivir) with antiviral activity against
influenza viruses licensed by the U.S. Food and Drug Administration for
the treatment and/or prevention of influenza. Controlled clinical trials
have demonstrated the efficacy of all four antiviral medications in
reducing symptom duration when used for treatment of influenza
infections. However, the medications may not always work, because
influenza virus strains can become resistant to one or more of these
medications.

**Otitis media:** A bacterial or viral infection of the middle ear.

**Outbreak:** Sudden appearance of a disease in a specific geographic
area (such as a neighborhood or community) or population (e.g.,
adolescents).

**P**

**Pandemic**: An epidemic occurring over an especially wide geographic
area, usually across multiple continents. Many people quickly become
ill, and sickness spreads to different countries and continents.
Pandemics are unusual events and their timing cannot be predicted. They
occur when a new (novel) influenza A virus emerges and spreads globally.

**Pandemic phases:** The World Health Organization (WHO) has defined six
draft pandemic phases for planning purposes. They are:

### [Interpandemic period]{.underline} 

Phase 1**:** No new influenza virus subtypes have been detected in
humans. An influenza virus subtype that has caused human infection may
be present in animals. If present in animals, the risk of human
infection or disease is considered to be low.

Phase 2: No new influenza virus subtypes have been detected in humans.
However, a circulating animal influenza virus subtype poses a
substantial risk of human disease.

### [Pandemic alert period]{.underline} 

Phase 3**:** Human infection(s) with a new subtype but no human-to-human
spread, or at most, rare instances of spread to a close contact.

Phase 4: Small cluster(s) with limited human-to-human transmission but
spread is highly localized, suggesting that the virus is not well
adapted to humans.

Phase 5: Larger cluster(s) but human-to-human spread still localized,
suggesting that the virus is becoming increasingly better adapted to
humans but may not yet be fully transmissible (substantial pandemic
risk).

### [Pandemic period]{.underline} 

Phase 6**:** Pandemic: increased and sustained transmission in general
population.

**Pathogens:** Bacteria, viruses, parasites, or fungi that can cause
disease.

**Patient flow:** The phrase refers to management and coordination of
treatment in a health care facility, especially during an emergency
situation. For example, when large numbers of people seek or require
health care during an influenza pandemic, it is important to have a plan
for intake, proper patient identification, isolation criteria, and other
procedures that depend on human resources and facility preparedness.

**Prophylaxis:** See chemoprophylaxis.

**Public Health Laboratory Information System (PHLIS):** A PC-based
software application designed for public health laboratories.
Laboratories use the system to report and analyze conditions of public
health importance that have a significant laboratory testing component.
PHLIS provides easy-to-use data collection screens, pre-formatted data
analysis tools, programmed telecommunications functions for transmitting
data to CDC and state locations, and data management utilities.

**Q**

**Quarantine:** Quarantine is a strategy used by public health
authorities to contain the spread of a contagious illness. It involves
the separation of people who have been exposed to a certain illness and
may be infected but are not yet sick in order to stop the spread of that
illness. Quarantine is medically very effective in protecting the public
from some diseases by stopping the spread of that illness.

**R**

**Reagent:** A substance used to produce a chemical reaction to detect,
measure, and produce other substances.

**Reservoir:** An alternate or passive host or carrier that harbors
pathogenic organisms, without injury to itself, and serves as a source
from which other individuals can be infected.

**Respiratory hygiene:** Procedures to contain infectious respiratory
secretions in people showing symptoms of disease, beginning at initial
point of encounter. For example, usual respiratory hygiene for influenza
includes covering the mouth/nose when sneezing or coughing; using
tissues and disposing of them in no-touch containers; and careful hand
washing. (Also see Cough Etiquette).

**Rimantadine:** One of 4 prescription medications (along with
amantadine, oseltamivir, and zanamivir) with antiviral activity against
influenza viruses licensed by the U.S. Food and Drug Administration for
the treatment and/or prevention of influenza. Controlled clinical trials
have demonstrated the efficacy of all four antiviral medications in
reducing symptom duration when used for treatment of influenza
infections. However, all the drugs may not always work against different
influenza virus strains because these can become resistant to one or
more of these medicines. For example, analyses have shown that some H5N1
viruses isolated from poultry and humans in Southeast Asia are resistant
to amantadine and rimantadine.

**Risk Communication**- The communicator hopes to provide the receiver
with information about the expected type (good/bad) and magnitude
(weak/strong) of an outcome from a behavior or exposure. Usually this
refers to an adverse outcome due to an exposure and the probability of
the outcome occurring. Risk communication helps individuals make a
choice about whether or not to undergo medical treatment, or adjust to
the knowledge that something has already occurred (exposure) that may
put them at greater risk for a negative outcome.

**S**

**Seeding:** To implant microorganisms in a culture medium.

**Serology:** The branch of science dealing with the measurement and
characterization of antibodies and other immunological substances in
body fluids, particularly serum.

**Spanish influenza:** The common name of the influenza A virus
responsible for the 1918-1919 pandemic.

**Strain:** A specific genetic variant of an organism. (Also see
Influenza viral strains).

**Surge capacity:** The resources a facility (such as a hospital) or
community can use to meet health needs of much larger numbers of people
than it usually serves. A primary issue during an influenza pandemic is
for medical facilities and local governments to assess their surge
capacity realistically and develop emergency strategies to cope as
effectively as possible when needed.

**Surveillance:** The ongoing, systematic collection and analysis of
data and the provision of information which leads to action being taken
to prevent and control an infectious disease.

**Swine Flu Program:** Vaccination program developed in response to an
outbreak of swine influenza in humans that occurred at Fort Dix, a
military base in New Jersey, in 1976.

**T**

**Thimerosal:** A mercury-containing preservative used in some vaccines
and other products since the 1930s. No harmful effects have been
reported from thimerosal at doses used in vaccines, except for minor
reactions like redness and swelling at the injection site. However, in
July 1999, the Public Health Service agencies, the American Academy of
Pediatrics, and vaccine manufacturers agreed that thimerosal should be
reduced or eliminated in vaccines as a precautionary measure. Today,
with the exception of some influenza vaccines, none of the vaccines used
in the U.S. to protect preschool children against 12 infectious diseases
contain thimerosal as a preservative. Influenza vaccine is currently
available both with thimerosal as a preservative and preservative-free.

**Trivalent inactivated vaccine (TIV):** A vaccine that includes three
virus strains which have been inactivated. The influenza vaccine given
each year is trivalent, in an effort to anticipate potential influenza
strains that may circulate during the annual influenza season. The
trivalent vaccine for influenza contains H1N1, H3N2, and B strains.

**Typing and subtyping:** The process by which virus strains are
identified through examination of clinical specimens.

**U**

**V**

**Vaccine:** A product that produces immunity therefore protecting the
body from the disease. Vaccines are administered through needle
injections, by mouth, and by aerosol.

**Vaccine Cold Chain:** Maintaining proper vaccine temperatures during
storage and handling to preserve potency.

**Vaccine Production:** Influenza virus vaccines usually are produced by
growing approved seed viruses in fertilized chicken eggs, purifying and
chemically treating the harvest (including inactivating infectivity),
and then adjusting the concentration against reference biological
standards. Seasonal influenza vaccine usually takes 4 -- 5 months
between inoculation of eggs and distribution of vaccine. Vaccine for
pandemic influenza raises special issues about composition and
packaging. Production of a vaccine against a highly pathogenic avian
influenza virus like the H5N1 virus now circulating among birds in Asia
is complicated by the fact that in its pure form, the virus kills the
inoculated eggs. In order to produce vaccine, the virus must be
genetically engineered to be less \"deadly\" before it can be grown in
eggs. This process, called reverse genetics, was utilized in the
production of the experimental avian flu vaccine currently undergoing
human trials by the National Institutes of Health.

**Vaccine Safety Datalink Project (VSD):** In order to increase
knowledge about vaccine adverse events, the Centers for Disease Control
and Prevention has formed partnerships with eight large Health
Management Organizations (HMOs) to continually evaluate vaccine safety.
The project contains data on more than 6 million people. Medical records
are monitored for potential adverse events following immunization. The
VSD project allows for planned vaccine safety studies as well as timely
investigations of hypotheses.

**Vector:** An organism that transmits an infective agent from one host
to another.

**Viral Shedding:** The process during which a virus is present in an
area of the body and is excreted (e.g., perspiration, saliva, or feces).
Adults can shed influenza virus from the day before getting symptoms to
approximately 5 days after symptoms start. Children can shed virus for
10 or more days. Shedding of influenza viruses can take place even if an
infected person is showing no symptoms of disease.

**Virus:** A strand of DNA or RNA in a protein coat that must get inside
a living cell to grow and reproduce. Viruses cause many types of
illness, including influenza, which is composed of RNA strands. Viruses
are not affected by antibiotics.

**W**

**X**

**Y**

**Z**

**Zanamivir:** One of four antiviral agents licensed by the Food and
Drug Administration for the treatment and/or prevention of influenza.
Unlike other antiviral agents, it is not licensed for use to prevent
influenza.