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Varicella Vaccine
Clinical
questions and answers about the varicella
vaccine
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Questions and links to
answers:
- What
is the varicella vaccine and what is its
dosage schedule?
- Can
varicella vaccine be given along with other
vaccines?
- How
effective is the varicella vaccine?
- Is
waning immunity a problem?
- Will
a booster vaccination be needed in the future?
- How
will varicella vaccine affect the epidemiology
of disease?
- Should
serologic testing be done prior to vaccination?
- What
lab tests are available to determine immunity?
- What
adverse events are associated with varicella
vaccine?
- If
serious adverse events occur, are there lab
methods that distinguish vaccine virus from
the wild virus?
- What
are the contraindications and precautions?
- What
data are available concerning transmission
of varicella vaccine virus to contacts?
- Will
post-exposure use of vaccine prevent or modify
varicella?
- Can
varicella vaccination be used to control
outbreaks?
Go to other pages of
related questions:
Varicella
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- What
kind
of vaccine is varicella? What
is its dosage schedule?
Varicella
vaccine is a live attenuated
virus vaccine that is administered
subcutaneously. For children
through age 12 years, it is administered
subcutaneously as a single 0.5ml
dose. Persons 13 years of age
and older should receive two
0.5ml doses subcutaneously 4-8
weeks apart.
- Can
the varicella
vaccine be given at the same
time as other vaccines?
Yes,
varicella vaccine can be given
at the same time as other
vaccines given routinely in
childhood. It is recommended
that for children 12-18 months
of age, the varicella vaccine
be given at the same time
as MMR vaccine or, when administered
separately, MMR and varicella
vaccine should be given at
least 28 days apart.
- How
effective
is the varicella vaccine in preventing
varicella disease?
Pre-licensure
studies of varicella vaccine
showed the vaccine to be 70-90%
effective in preventing disease
and more than 95% effective in
protecting against severe disease.
If a vaccinated person does get
varicella, it is usually a very
mild case with fewer lesions
(usually <50, which are frequently
not vesicular), mild or no fever,
and a quicker recovery. Investigations
of vaccine field effectiveness
since vaccine licensure have
demonstrated that vaccine provides
100% protection against moderate
to severe disease and most commonly
is effective in preventing 80-90%
of all disease. These data indicate
that the vaccine performs well
under conditions of community
use.
- Is
waning
immunity a problem with the varicella
vaccine?
The
length of protection/immunity
from any new vaccine is never
known when it is first introduced.
Available data from following
up children vaccinated in prelicensure
clinical trials indicate that
protection from varicella vaccine
lasts for at least 25 years (Japanese
data) and 14 years (U.S. data).
Experience with other live viral
vaccines (e.g. measles, rubella)
has shown that post vaccination,
immunity remains high throughout
life. For these vaccines, second
doses are needed to cover the
small percent of people who fail
to seroconvert after the first
dose (primary vaccine failure).
Follow-up studies continue to
assess levels of immunity in
vaccines as disease incidence
declines.
- Will
a booster
vaccination be needed in the
future?
Ongoing
studies and surveillance will
determine the need for, and if
appropriate, the timing of additional
doses in the future. At this
time, there is no recommendation
for a booster dose.
- How
will use of varicella
vaccine affect the epidemiology
the disease?
As
all vaccines have done, varicella
vaccine will affect the epidemiology
of the disease. Most importantly,
the incidence of disease will
decline in all age groups. This
is already occurring in sites
conducting active surveillance
for varicella. In 1999, there
was a dramatic decline in cases
and the expected spring time
increase in varicella cases did
not occur. As we would expect,
the greatest decline in incidence
has occurred among children 1-4
years; however, the decline in
incidence is occurring in all
age groups, including adults
who currently do not have recommendations
for varicella vaccine and infants
< 12 months who are not eligible
for vaccination. As transmission
continues to decline, decreasing
circulation of wild virus will
increase the likelihood that
unexposed and unvaccinated children
will enter adolescence and adulthood
without immunity. Thus, it is
increasingly important to offer
vaccine to all susceptible adolescents
and adults as well as children
in line with current recommendations.
The Advisory Committee on Immunization
Practices (ACIP), American Academy
of Pediatrics (AAP), and American
Academy of Family Physicians
(AAFP) recommend vaccination
at 12-18 months and catch-up
vaccination of all susceptible
children and adolescents in order
to prevent outbreaks at older
ages, when disease is more severe,
among older children who are
neither vaccinated nor exposed
to wild type virus.
- Should
serologic
testing be done prior to vaccination?
A
reliable history of varicella
is considered presumptive evidence
of immunity. However, if an adult
has a negative or uncertain history
of varicella, testing is likely
to be more accurate than relying
on history alone, since 70% to
90% of adults who do not have
a reliable history of varicella
are actually immune. Thus, serologic
testing before vaccination is
likely to be cost-effective since
the cost of a lab test ($25-$75)
is usually less than vaccination
(approximately $100 for two doses
of vaccine). Depending on the
cost of the laboratory test it
may also be cost-effective to
determine the serologic status
of older children with negative
or uncertain histories of varicella
prior to vaccination. However,
testing is not required and the
vaccine is well-tolerated in
persons who are immune.
- What
laboratory
tests are available to determine
varicella immunity prior to vaccination?
The
most common commercially available
test is the EIA (enzyme immunoassay).
This test is sensitive enough
to determine immunity following
natural disease, but may not
be sensitive enough for determining
immunity following vaccination
when antibody levels are lower.
The serology test used to determine
immune response to varicella
vaccine during the clinical
trails, the gpELISA test, is
not available commercially.
Thus, serological results obtained
following vaccination must
be interpreted with caution
since some commercially available
tests are not sensitive enough
to detect low levels of antibody
post-vaccination. Other tests
with higher sensitivity than
the commercially available
EIA such as the FAMA (flourescent
antibody-to-membrane antigen)
assay requires extensive experience
and is performed only in a
few academic laboratories.
A VZV latex bead agglutination
assay is now commercially available
that is more sensitive than
most conventional EIAs.
- What
adverse
events are associated with
varicella vaccine?
Varicella
vaccine is very safe. Although
vaccine recipients in uncontrolled
trials reported minor injection
site complaints (20% reported
pain, swelling or redness) and
rashes (3%-5% reported a localized
rash, and an additional 3%-5%
developed a generalized varicella-like
rash 5-26 days after vaccination),
the rate of adverse events was
much lower in the only randomized,
controlled clinical trial conducted
in children. In this trial 1%
of vaccine recipients developed
injection site rash compared
with 0.3% of placebo recipients
and 3.2% of vaccine recipients
developed generalized rash compared
with 1.7% of placebo recipients.
These rashes had an average of
2-5 lesions and were likely to
be maculopapular rather than
vesicular. The incidence of fever
did not differ between the vaccination
and placebo groups. Experience
with the first 11 million doses
distributed show that very infrequently
(in approximately 2.8 per 100,000
doses given) serious adverse
events such as seizures, encephalitis,
pneumonia, anaphylaxis and death
have occurred. Note: Reporting
a serious adverse event after
vaccination does not indicate
a causal association between
vaccination and the event. Physicians
should report serious adverse
events to the Vaccine Adverse
Event Reporting System (VAERS)
at 1-800-822-7967.
For
more information, visit
the following site:
http://vaers.hhs.gov
Updated
ACIP recommendations:
http://www.cdc.gov/epo/mmwr/preview/mmwrhtml/rr4806a1.htm
- For
serious adverse events that
occur after varicella vaccination,
are there laboratory methods
that distinguish the vaccine
virus from the wild virus?
Yes,
CDC’s National VZV Laboratory
provides VZV strain discrimination
testing to state and local public
health organizations and to private
physicians in cases of suspected
adverse events following vaccination.
The laboratory offers free testing
for suspected adverse events
such as:
- Individuals
who develop > 50 lesions
7-42 days post vaccination;
- Individuals
who develop certain serious
adverse experiences post vaccination
including pneumonia, pneumonitis,
cerebritis (encephalitis),
cerebellitis (cerebellar ataxia)
and aseptic meningitis;
- Herpes
zoster post vaccination;
- Suspected
cases of secondary transmission
of the vaccine virus;
- Pregnant
women who inadvertently receive
varicella vaccine or who have
been exposed to a vaccinee
and who develop a varicella
rash.
The
contact phone number at the National
VZV Laboratory for information
on this service including how
to collect and transport specimens
is (404) 639-0066.
The
National VZV Laboratory is also
equipped to provide VZV serological
testing and VZV diagnostic testing
including strain discrimination
for cases of severe disease or
death believed to be related
to VZV infection, and for suspected
breakthrough infections with
VZV and for VZV outbreaks.
- What
are the
contraindications and precautions
to varicella vaccination?
Varicella
vaccine should not be given to
persons who are allergic to any
component of the vaccine or who
have had a severe allergic reaction
to a prior dose of vaccine. The
vaccine contains neomycin and
gelatin, but does not contain
preservatives or egg protein.
Although
the vaccine is not licensed for
persons with blood dyscrasias,
leukemia, lymphoma or malignant
neoplasms affecting the bone
marrow or lymphatic system, the
vaccine is available at no cost
for a limited group of patients
with acute lymphoblastic leukemia
(ALL) through a research protocol.
In 1999, ACIP altered its recommendations
for the use of varicella vaccine.
The committee continued to contraindicate
the vaccine for persons with
cellular immunodeficiences but
removed the restriction on vaccination
of persons with defects of humoral
immunodeficiency. In addition,
ACIP suggested that physicians
consider vaccinating a subset
of HIV-infected children who
are in CDC Class N1 or A1 and
have an age-specific CD4% >25%.
These children should receive
2 doses of the vaccine separated
by 3 months.
As
was previously recommended, the
following groups of persons should
not be vaccinated:
- persons
taking large doses of corticosteroids
(>2mg/kg of body weight
or >20mg/day of prednisone
or its equivalent);
- persons
with a moderate or severe concurrent
illness;
- women
who are pregnant;
- persons
who have received blood products
(such as whole blood or immune
globulin) during the previous
5 months;
- and
persons with a family history
of congenital hereditary immunodeficiency
in first degree relatives unless
they are known to be immunocompetent.
Caution
is advised when immunizing children
receiving salicylates. No adverse
events associated with the use
of salicylates after varicella
vaccination have been reported.
However, the vaccine manufacturer
recommends that vaccine recipients
avoid using salicylates for 6
weeks after receiving varicella
virus vaccine because of the
association between aspirin use
and Reye syndrome following varicella.
Vaccination with subsequent close
monitoring should be considered
for children who have rheumatoid
arthritis or other conditions
requiring therapeutic aspirin.
For
further information, visit the
following site:
http://www.cdc.gov/epo/mmwr/preview/mmwrhtml/rr4806a1.htm
See
also Recommendations
for Postexposure Prophylaxis
of Varicella of Persons at High
Risk for Severe Disease
- What
data
are available concerning transmission
of varicella vaccine virus to
contacts?
Available
data suggest that the risk of
vaccine virus transmission from
healthy vaccinees is very low
and occurs only if the vaccinee
has a rash. With the currently
licensed vaccine, there have
been 3 documented cases of transmission
from healthy vaccinated children.
The risk for transmission from
vaccinees who are immunocompromised
is higher.
-
Will
post-exposure use of the
vaccine prevent or modify varicella?
Yes,
the vaccine may prevent or
modify illness when administered
within 3 to 5 days after exposure.
The ACIP now recommends vaccination
of susceptible persons who
are eligible for vaccination
as soon as possible after exposure--ideally
within 3 days but possibly
up to 5 days of an exposure--to
prevent illness or modify disease
severity. If a person has already
been infected, and the vaccine
is given soon enough, disease
may be modified or prevented.
If the person was infected
>5 days prior to vaccination,
there is unlikely to be any
benefit from vaccination but
vaccination is not known to
be harmful. Finally, exposure
even in a household setting
does not result in transmission
100% of the time. So, if the
exposed person has not been
infected, vaccination will
confer protection against subsequent
exposures.
For
further information, visit
the following site:
http://www.cdc.gov/epo/mmwr/preview/mmwrhtml/rr4806a1.htm
- Can
vaccination
be used to control outbreaks
of varicella?
Varicella
outbreaks in closed settings
(e.g. child care centers, schools,
institutions) tend to be protracted
and go through several generations
of infection before coming to
an end in the absence of an intervention.
School outbreaks have been documented
to last for 3-6 months. Varicella
vaccine has been used successfully
by state and local health departments
and by the military for outbreak
prevention and control. Although
the vaccine works by preventing
illness or modifying the severity
of illness in those vaccinated
within 3 days and possibly up
to 5 days after exposure, most
of the benefit of vaccinating
all susceptible individuals in
an outbreak in a closed setting
derives from vaccinating persons
before exposure, since few individuals
are actually infected in the
first generation. For this reason,
although it is desirable to intervene
as early in an outbreak as possible,
it is still useful to intervene
at any point after the outbreak
has been recognized and before
all susceptible individuals have
contracted illness. Intervening
with vaccination can decrease
the number of cases in an outbreak
and shorten the outbreak’s duration.
For
further information, visit the
following site:
http://www.cdc.gov/epo/mmwr/preview/mmwrhtml/rr4806a1.htm
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