The purpose of the active surveillance program is to
obtain population-based incidence rates for varicella
and herpes zoster diseases in a community with established
high varicella vaccination coverage rates and to evaluate
the impact of current and future varicella vaccination
practices and policies. In addition to active surveillance,
numerous epidemiological studies are ongoing throughout
the year and information from the studies is presented
at various conferences and publications.
Contents of this page:
is a cooperative agreement funded by the Centers for Disease
Control and Prevention (CDC) and implemented by the Philadelphia
Department of Public Health and the Los Angeles County Department
of Health Services since 1995. The purpose of the active surveillance
program is to obtain population-based incidence rates for
varicella and herpes zoster diseases in a community with established
high varicella vaccination coverage rates and to evaluate
the impact of current and future varicella vaccination practices
and policies. In addition to active surveillance, numerous
epidemiological studies are ongoing throughout the year and
information from the studies is presented at various conferences
The Varicella Active Surveillance
Project (VASP) is a cooperative agreement funded by the Centers
for Disease Control and Prevention (CDC) in September 1994
develop a reporting system to accurately define the baseline
incidence and epidemiological profile of varicella disease
prior to licensure and wide use of varicella vaccine,
identify changes in the epidemiology of varicella as a result
of vaccine usage,
the immunization status of cases, and
evaluate the demographic and clinical profiles of vaccinated
and unvaccinated cases of varicella.
were originally 3 areas under surveillance: Travis County,
TX, Antelope Valley, CA, and West Philadelphia, PA. Currently,
only Antelope Valley (implemented by the Los Angeles County
Health Department) and West Philadelphia (implemented by the
Philadelphia Department of Public Health) project areas are
Implement, conduct, maintain, and evaluate active population-based
surveillance systems with capacity to monitor varicella
and herpes zoster diseases.
Perform case investigations for varicella and herpes zoster
for all ages and collect, analyze and disseminate information
using these data.
Collect and report information on vaccine doses administered
by age group.
Develop, implement and evaluate varicella prevention and
control strategies including outbreak control.
Provide laboratory specimens for laboratory evaluation needed
for varicella and herpes zoster surveillance or as part
of epidemiological studies, e.g., virus strain identification,
confirmation of breakthrough disease, and molecular epidemiological
Conduct applied epidemiological studies for varicella and
herpes zoster diseases in order to contribute to the immunization
program policy and guidelines.
Cases of varicella and herpes zoster are reported
by 300 participating reporting sites in each surveillance
area, including hospitals, public and private schools, primary
care practitioners, public health clinics, licensed child-care
facilities, prisons, homeless shelters, and universities.
Case identification is facilitated through a standardized
surveillance system in which each surveillance site reports
twice a month to VASP the presence or absence of varicella
and herpes zoster within their facility. Billing records are
obtained from local healthcare systems and public health clinics
to identify cases which may not have been reported during
After notification, each case, or his/her parent/guardian,
is interviewed via telephone or house visit to confirm diagnosis
and to obtain detailed clinical and demographic information.
The interviewer assesses whether there are additional cases
or susceptible contacts within the household. A case investigation
is completed for each newly identified case of varicella.
To improve case ascertainment, all household contacts without
a positive history of varicella disease are re-contacted in
3 weeks (one incubation period) after the onset of the most
recent case to investigate potential household spread of varicella
infection. If there is more than one susceptible contact living
within a household, the contacts are followed for 6 weeks
or 2 incubation periods.
Laboratory confirmation of cases has become increasingly important.
The VASP offices along with CDC work with the sites to help
expand specimen collection for laboratory testing. All specimens
are sent to CDC's National Varicella Zoster Virus (VZV) Laboratory
for testing. Common diagnostic or confirmatory tests performed
include: VZV IgG gpELISA, VZV IgM ELISA, PCR, and RFLP.
In 1995, there were 2934 verified cases reported in Antelope
Valley, CA, 3130 cases in Travis County and 1197 cases in
West Philadelphia. The number of cases declined in all sites
in 1996 and remained stable until 1998. In 1999, the number
of cases began to dramatically decrease and in 2000, there
were 837, 491, and 250 cases in Antelope Valley, Travis County,
and West Philadelphia respectively. Between 1995 and 2000,
the total number of cases in the three surveillance areas
declined 71% to 84%, with the most considerable reduction
in preschool children (1-4 year olds). By 2004, the number
of cases declined by about 85% in both Antelope Valley and
West Philadelphia combined.
image to enlarge
There were 34 to 53 hospitalizations between 1995 though 1998
for all sites, which decreased to 8 hospitalizations in 1999
and 20 hospitalizations in 2000. Hospitalization rates ranged
from 2.7 to 4.2 per 100,000 population from 1995 to 1998 and
decreased to 0.6 per 100,000 in 1999 and 1.5 per 100,000 in
2000. From the results of the National Immunization Survey
(NIS), the annual varicella-related hospitalization rates
have shown to have declined to 0.13 hospitalizations per 10,000
U.S. population in 2001 compared to a rate that exceeded 0.5
hospitalizations per 10,000 U.S. population from 1993 to 1995.
From data provided by the National Center for Health Statistics
(NCHS), the number of deaths with varicella listed as an underlying
cause has declined 78%, decreasing from 0.41 deaths per 1,000,000
in 1990-1994 to 0.14 in 1999-2001. The greatest reduction
in mortality rates occurred among children aged 1 to 4 years.
in vaccination coverage
Vaccination coverage has increased for children between the
ages of 19 and 35 months since 1997. In Los Angeles County,
vaccination coverage increased from 40% in 1997 to 95.2% in
2003. In Philadelphia, vaccination coverage increased from
43% in 1997 to 90.0% in 2003. A similar increase in vaccination
coverage seen from the VASP sites is reflected nationally:
from nation-wide data, vaccination coverage in children aged
19-35 months increased from 25.8% in 1997 to 84.8% in 2003.
Seward JF. Watson BM. Peterson CL. Mascola L. Pelosi JW.
Zhang JX. Maupin TJ. Goldman GS. Tabony LJ. Brodovicz KG.
Jumaan AO. Wharton M. Varicella disease after introduction
of varicella vaccine in the United States, 1995-2000. JAMA
National Immunization Survey. Available from:
CDC. National, state, and urban area vaccination coverage
levels among children aged 19-35 months –United States,
2000. MMWR Morb Mort Wkly Rep 2004; 53(29):658-661. http://www.cdc.gov/mmwr/preview/mmwrhtml/mm5329a3.htm
HQ, Jumaan AO, Seward JF. Decline in varicella mortality
following implementation of varicella vaccination in the
United States. NEMJ 2005; 352(5):450-458.
- Davis MM, Patel MS, Gebremariam A. Decline
in varicella-related hospitalizations and expenditures for
children and adults after introduction of varicella vaccine
in the United States. Pediatrics 2004; 114(3):786-792.
the Philadelphia Department of Public Health, the VASP project
is carried out by the Division of Disease Control. West Philadelphia
includes 7 zip codes with a total population of approximately
300,000. Twenty-six percent of the individuals in the West
Philadelphia surveillance area are less than 18 years of age
and there is a 0.85 male to female ratio. Based on the 2002
Census statistics, the population is composed of 75.8% African
Americans, 16.4% Caucasians, and 7.8% listed as Asian or other
ethnicity/race. Within this surveillance area, there is significant
variation in the income, level of education, and presence
of risk factors. The median household income for each zip
ranges from 15,888 to 38,668. Among the adults over 25, 68%
have completed high school.
Valley of Los Angeles
the Los Angeles Department of Health Services, VASP project
is conducted in the Antelope Valley health district. Antelope
Valley is a high desert community located in the northeastern
part of Los Angeles County (LAC) and consists of approximately
35 communities, covering approximately 2000 square miles.
It is located 35 miles from downtown Los Angeles, and is relatively
isolated from the larger, dense areas of LAC. The health district
primarily includes the cities, Lancaster and Palmdale, with
63% of the community living in one of these two cities. There
are a total of 282 reporting sites, representing 313 surveillance
units participating in VASP.
Valley is an area that has been attracting younger populations,
in particular young couples and families. Approximately 34.6%
of the population is between 1-19 years of age and 47.6% is
between 20-54 years of age. Based on 2003 Census statistics,
the total population in Antelope Valley is approximately 348,943
and is composed of 48.9% Caucasians, 31.5% Hispanic, 15.5%
African Americans, and 4.1% listed as Asian, American Indian
or Pacific Islander.
(varicella) is an infectious disease caused by the varicella
zoster virus (VZV), a member of the herpes virus family. Infection
usually leads to a blister-like rash, itching, tiredness,
and fever. Chickenpox is highly infectious and can spread
from person to person from direct contact or through the air
from an infected person’s coughing or sneezing. A person
with chickenpox is contagious 1-2 days before rash appears
and until all blisters have formed scabs. It takes approximately
10-21 days after contact with an infected person for someone
to develop chickenpox.
causes an illness that lasts commonly 5-6 days in children.
Symptoms can include high fever, severe itching, uncomfortable
rash, dehydration, or headache. Occasionally, serious complications
from disease can occur, including bacterial infections in
the skin, tissues, bone, lungs, joints, or blood; viral pneumonia;
bleeding problems; and encephalitis (infection of the brain).
can be usually prevented by receiving the varicella vaccine,
Varivax. The vaccine was licensed in 1995 by Merck and has
been shown to be 70 to 90% effective against preventing disease.
According to recommendations set by the Advisory Committee
on Immunization Practices (ACIP), children between the ages
of 12 to 18 months should be administered one dose of vaccine,
and children between 19 months and 13 years, who have not
had the chickenpox should also be vaccinated with a single
dose. Children with prior history of chickenpox disease do
not need to be vaccinated. Individuals 13 years and older
who have not had chickenpox should receive two doses of the
vaccine 4 to 8 weeks apart.
of varicella may occur in some vaccinated persons following
exposure to wild-type virus. This is called breakthrough infection.
Breakthrough infection is varicella disease
that occurs more than 42 days after vaccination following
exposure to wild-type varicella zoster virus and usually results
in mild illness. Nonetheless, breakthrough varicella is contagious
and can lead to transmission of virus to those unvaccinated
and at risk for complications, such as adults, immunocompromised
individuals, and pregnant women.
of Breakthrough Chickenpox: Abdomen of child with breakthrough
Click image to enlarge
image to enlarge
of Breakthrough Chickenpox: Back of child with breakthrough
image to enlarge
skin lesions of breakthrough varicella can be macular
rather than vesicular. They are rarely bullous or hemorrhagic,
and residual scarring is less common.
CDC. Prevention of varicella: recommendations of the Advisory
Committee on Immunization Practices (ACIP). MMWR 1996;45(No.
CDC. Prevention of varicella: update recommendations of
the Advisory Committee on Immunization Practices (ACIP).
MMWR 1999;48 (No. RR-6). http://www.cdc.gov/mmwr/preview/mmwrhtml/rr4806a1.htm
Watson BM. Piercy SA. Plotkin SA. Starr SE. Modified chickenpox
in children immunized with the Oka/Merck varicella vaccine.
Pediatrics 1993; 91:17-22.
Bernstein HH. Rothstein EP. Watson BM. Reisinger KS. Blatter
MM. Wellman CO. Chartrand SA. Cho I. Ngai A. White CJ. Clinical
survey of natural varicella compared with breakthrough varicella
after immunization with live attenuated Oka/Merck varicella
vaccine. Pediatrics 1993; 92:833-837.
Seward JF, Zhang JX, Maupin TJ, Mascola L, Jumaan AO. Contagiousness
of varicella in vaccinated cases. JAMA 2004; 292 (6):704-8.
topics on National Immunization Program's website:
Varicella information on Immunization Action Coalition's website:
Vaccine Information Statement on NIP's website:
(herpes zoster) is a common illness with increasing
incidence and severity as age advances. It is caused by the
varicella-zoster virus (VZV), which also causes chickenpox.
The mechanism of infection is not fully understood, but it
involves the reactivation of latent virus activity in the
cranial and dorsal root ganglia. Shingles patients can transmit
VZV to susceptible individuals (i.e., those who have not had
chickenpox or were not vaccinated previously). Some studies
have hypothesized that exposure to the virus (mostly by contact
with cases of chickenpox) may reduce the likelihood of developing
image to enlarge
of the trunk of a shingles patient with typical dermatomal
rash with hemorrhagic vesicles.
Stankus SJ. Dlugopolski M. Packer D. Management of herpes
zoster (shingles) and postherpetic neuralgia. American
Family Physician 2000 April 15; 61(8):2437-44, 2447-8.
of Herpes Zoster: Image of trunk and back of
individual with shingles.
Lau BH. Lin MI. Lin HC. Herpes zoster during varicella.
Pediatric Infectious Disease Journal 2001 September;
zoster can occur after varicella vaccination among otherwise
healthy children. However, a population-based study indicated
that the incidence of shingles in vaccinated children is lower
than compared to unvaccinated children with natural disease.
Guess HA. Broughton DD. Melton LJ 3rd. Kurland LT. Epidemiology
of herpes zoster in children and adolescents: a population-based
study. Pediatrics 1985 Oct; 76(4):512-7.
K, Watson BM, Perella DM, Robinson D.
Outbreak Control and Prevention Policy (OCPC) for Philadelphia
during the 2003-2004 School Year. 39th National Immunization
Conference, Washington D.C., March 2005.
D, Perella DM, Spain CV, Fiks A, Gargiullo P, Watson BM,
Heath K, Pletcher J, Forke C, Schmid S.
of Reported Varicella History as a Marker for Varicella-Zoster
Virus (VZV) Immunity among Different Age Groups. 39th
National Immunization Conference, Washington D.C., March
M, Watson BM, Gargiullo P, Perella DM, Heath K, Tillach
of Herpes Zoster Diagnoses among City of Philadelphia
District Health Center Patients. 39th National Immunization
Conference, Washington D.C., March 2005.
ZS, Seward JF, Watson BM, Maupin TJ, Jumaan AO
or Smallpox: The use of Febrile Prodrome as a Distinguishing
Characteristic. Clin Infect Dis. 2004 Dec 15;39(12):1810-7.
JF, Zhang JX, Maupin TJ, Xiao H, Mascola LM, Jumaan AO
of Varicella in Vaccinated cases: A household contact
study. JAMA 2004; 292(6):704-8.
RH, Maupin TJ, Xiao H, Seward JF, Jumaan AO, Mascola L
Population - Based Study of Herpes Zoster in Children
and Adolescents Post-Varicella Licensure, Antelope Valley,
2000-2003. 38th National Immunization Conference, Memphis,
TN, May 2004.
RH, Maupin TJ, Xiao H, Mascola L, Jumaan AO
in Varicella Outbreaks in Antelope Valley, California
1995 - 2003. 42nd Annual Meeting of Infectious Disease
Society of America (IDSA), Boston, MA, October 2004.
TJ, Goldman GS, Peterson CL, Mascola L, Jumaan, AO
Susceptibility Among Adolescents in an Active Surveillance
Site. 36th National Immunization Conference, Denver, CO,
May 1 2002.
S, Maupin TJ, Seward JF, Jumaan AO, Peterson C, Goldman
G, Mascola L, Wharton M
Varicella Infections: Are they more common than previously
thought? Pediatrics 2002; 109(6):1068-73.
JF, Watson BM, Peterson CL, Mascola L, Pelosi JW, Zhang
JX, Maupin TJ, Goldman GS, Tabony LJ, Brodovicz KG, Jumaan
AO, Wharton M
Disease After Introduction of Varicella Vaccine in the
United States, 1995 -2000. JAMA 2002; 287(5):606-11.
TJ, Goldman G, Peterson CL, Mascola L, Seward JF
Attitudes and Practices of Healthcare Providers Regarding
Varicella Vaccination in Sentinel Surveillance Area, 1996,
1997 and 1999. Pediatric Academic Society Meeting, Baltimore,
MD, April-May 2001.
GS, Glasser JW, Maupin TJ, Peterson CL, Mascola L, Chen
RT, Seward JF
Impact of Vaccination on Varicella Incidence Conditional
on School Attendance and Temperature, in Antelope Valley,
California. Pharmacoepidemiology and Drug Safety, Barcelona,
Spain, August 22, 2000.
factors for vaccine failure
live attenuated vaccine to prevent varicella-zoster virus
(VZV) infection was licensed in the United States (U.S.) in
March 1995. Prior to vaccine licensure, approximately four
million cases of varicella were estimated to occur annually
in the U.S., including 11,000–13,500 hospitalizations
and 100-150 deaths. Varicella vaccine provides 70 to 90% protection
against any disease and at least 95% protection against severe
disease. Only three studies have documented a vaccine-effectiveness
of less than 60%. The varicella vaccination program has been
successful in reducing the varicella disease burden in the
U.S. Nevertheless, despite its substantial impact on reducing
varicella morbidity and mortality, varicella disease among
vaccinated school-age children continues to be described.
Some researchers have suggested that possible reasons for
varicella disease even among highly vaccinated persons may
be related to the age at vaccination and waning immunity after
vaccination. However, majority of the studies have not been
able to confirm age at vaccination and time since vaccination
as risk factors for vaccine failure. Available data do not
support a delay in the earliest recommended age of immunization
because of the risk of leaving children unprotected for additional
months and the possibility that such children might not return
later for vaccination. In addition, the vaccine effectiveness
estimated in school-based outbreaks has ranged most commonly
from 80% to 85% - within the range of pre-licensure efficacy
calculated in clinical trials (70%-90%). These observations
have been consistent with lack of waning immunity in the vaccinated
plays an important role in the monitoring of vaccine effectiveness
over time. Although disease is much milder and the number
of cases declined substantially due to a vaccine efficacy
of 70-90%, varicella continues to occur at a low rate and
cause outbreaks. Currently, the Advisory Committee on Immunization
Practices (ACIP) is reviewing data to determine whether a
second dose of varicella vaccine should be considered.
zoster after widespread vaccine use
have been raised over whether the reduction in circulating
VZV due to the varicella vaccination program will increase
the incidence of herpes zoster. Mathematical models based
on the assumption that protection against reactivation of
VZV is a result of external boosting (i.e., exposure to cases
of varicella disease) alone have suggested that significant
increases in herpes zoster incidence will occur over the next
30-50 years. However, the triggers for reactivation of VZV
are poorly understood, and protection may involve external
boosting, internal boosting, or other mechanisms.
response to these concerns, VASP is collecting thorough information
on herpes zoster cases. Cases of shingles have been reported
to VASP since 1999 among individuals <20 years. Currently,
both surveillance areas will expand their reporting system
to capture cases of shingles identified in all ages. The surveillance
for shingles will also be important with the possible licensure
of the new vaccine for herpes zoster.
in the diagnosis of varicella
to the licensure of the vaccine, varicella was primarily diagnosed
clinically because wild-type varicella disease is easily distinguishable
based on its characteristic vesicular rash. However, it is
more difficult to diagnose breakthrough varicella cases using
traditional clinical methods because the manifestations of
the disease are oftentimes mild and more easily mistaken for
other diseases that cause rash, including herpes simplex,
rickettsial pox, impetigo, allergic reactions, and insect
bites. Although epidemiologic information will still play
an important role, laboratory tests will also be more heavily
relied on for the diagnosis of varicella, although at this
time, some of these tests are still not readily available
at all clinics and physician offices. VASP offers the service
of laboratory testing for all their reporting units. At this
time, there is no published study that examines the characteristics
of the rash produced by breakthrough disease and for this
reason, VASP is currently conducting studies to examine the
epidemiology and the best diagnostic tools for detecting breakthrough
Council of State and Territorial Epidemiologists (CSTE) recommended
that states establish case-based surveillance by 2005. Case-based
reporting was implemented in previous years in the two VASP
sites, West Philadelphia, PA and Antelope Valley, CA, and
has shown to be a useful and feasible component of their surveillance
project. Extending case-based reporting nationwide will help
to provide more information to monitor the epidemiology of
varicella and allow us to better monitor the impact of the
immunization program. More information on varicella case-based
reporting can be found at: http://www.cdc.gov/nip/ed/ciinc/January_05.htm
Galil K. Lee B. Strine T. Carraher C. Baughman AL. Eaton
M. Montero J. Seward J. Outbreak of varicella at a day-care
center despite vaccination. New England Journal of Medicine
Galil K. Fair E. Mountcastle N. Britz P. Seward J. Younger
age at vaccination may increase risk of varicella vaccine
failure. Journal of Infectious Diseases 2002; 186(1):102-5.
BR, Feaver SL, Miller CA, Hedberg CW, Ehresmann KR. An elementary
school outbreak of varicella attributed to vaccine failure:
policy implications. Journal of Infectious Diseases 2004;190(3):477-83.
Epub 2004 Jun 29.
for Disease Control and Prevention. Outbreak of varicella
among vaccinated children--Michigan, 2003. MMWR 2004; 53(No.
Vazquez M. Varicella infections and varicella vaccine in
the 21st century. Pediatric Infectious Disease Journal 2004;
Vazquez M. LaRussa PS. Gershon AA. Niccolai LM. Muehlenbein
CE. Steinberg SP. Shapiro ED. Effectiveness over time of
varicella vaccine. JAMA 2004; 291(7):851-5.
Garnett GP et al. The epidemiology of varicella-zoster virus
infections: the influence of varicella on the prevalence
of herpes zoster. Epidemiol Infect 1993; 108:513-28.
Thomas SL. Wheeler JG. Hall AJ. Contacts with varicella
or with children and protection against herpes zoster in
adults: a case-control study. Lancet 2002; 360: 678-82.
Brisson M. Gay NJ. Edmunds WJ. Andrews NJ. Exposure to varicella
boosts immunity to herpes zoster: implications for mass
vaccination against chickenpox. Vaccine 2002; 20: 2500-07.
T, Jumaan AO, Mullooly JP, Seward JF, Izurieta HZ, DeStefano
F, Black SB, Chen RT. Vaccine Safety Datalink Research Group.
A Retrospective cohort study of the association of varicella
vaccine failure with asthma, steroid use, age at vaccination,
and measles-mumps-rubella vaccination. Pediatrics 2003;112(2):e98-e103.
BD, Lee LE, Gillette H, Lorber EM, Hedberg K, Cieslak PR.
Chickenpox outbreak in a highly vaccinated school population.
DM, Watson BM, Heath K, Robinson D, Spain CV. Laboratory
confirmation of suspected breakthrough varicella infections.
Pediatric Academic Society Meeting, San Francisco, CA, May
RH, Maupin TJ, Xiao H, Seward JF, Jumaan AO, Mascola L.
A population-based study of Herpes Zoster (HZ) in children
and adolescents post-varicella vaccine licensure. 41st Annual
Meeting of Infectious Disease Society of America, San Diego,
CA, October 2003.
- Civen RH, Maupin TJ, Xiao H, Mascola L,
Jumaan AO. Trends in Varicella outbreaks in Antelope Valley,
California 1995-2003. 42nd Annual Meeting of Infectious
Disease Society of America, Boston, MA, October 2004.
for Disease Control
National Immunization Program
1600 Clifton Rd, Mail Stop E61
Atlanta, GA 30333
For immunization info, call the CDC-INFO
English and Spanish: 1-800-CDC-INFO
City of Philadelphia Department of Public Health
Division of Disease Control
500 S. Broad Street
Philadelphia, PA 19146
Main Phone 215-685-6741
Immunization Program Fax 215-685-6806
Disease Control Fax 215-545-8362
Department of Health Services- Public Health
High Desert Hospital
44900 N. 60th St. West
Lancaster, CA 93536
Phone: (818) 487-0063
Fax: (818) 487-0110
Immunization Program (NIP):
for Disease Control and Prevention (CDC):
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page last modified on March 28, 2005