• Lopez AS, et al. “Epidemiology of Varicella During
the 2-Dose Varicella Vaccination Program — United
States, 2005–2014.” MMWR Morb Mortal Wkly Rep.
Prior to implementation of the U.S. varicella vaccination program, approximately 4 million varicella cases,
11,000-13,500 hospitalizations related to varicella and
100-150 varicella-related deaths occurred annually.
Beginning in 1996, one dose of varicella vaccine was
routinely recommended during childhood. This led to
a 90% decrease in varicella incidence over the follow-
ing decade; however, outbreaks continued to occur. In
2006, a two-dose vaccine schedule at 12-15 months
and 4-6 years of age was implemented.
The decline in varicella incidence after introduction
of routine vaccination enabled varicella surveillance
through the National Notifiable Disease Surveillance
System (NNDSS), with state monitoring and reporting of cases to the Centers for Disease Control and
NNDSS data demonstrate a 72% decrease in varicella
incidence after initiation of the two-dose schedule, com-
pared to the one-dose schedule, from 2006-’ 10. Data
from 2013-’ 14 demonstrate that the average annual var-
icella incidence decreased by 85% ( 4 cases per 100,000
population) compared to 2005-’06 ( 25 cases per 100,000
population). Declines in incidence were noted in all age
groups, with the largest declines among children 5-9 years
(89%) and 10-14 years (85%) (see figure).
Among 12,784 cases (60%) with vaccination status
data available, 55% ( 7,000 cases) of varicella cases in
2013-’ 14 occurred among children who had received at
least one dose of vaccine, of which 1,345 had received
two or more doses. Hospitalization was required in 81
cases. Of those with disease severity documented, 49%
had moderate-severe disease based on the number of skin
lesions, and 51% had mild disease. Previously vaccinated
children who developed varicella had mild disease more
frequently than unvaccinated children (77% vs. 23%).
Dr. Raabe is a post-grad-uate training fellow in
pediatric and internal
medicine infectious diseases at Emory University
School of Medicine and
Children’s Healthcare of
Atlanta (CHOA). Dr.
Pickering was editor of the AAP Red Book from 2000-
’ 12. He is adjunct professor of pediatrics at Emory University School of Medicine and CHOA.
MMWR in Review
Dr. Raabe Dr. Pickering
by Vanessa Raabe, M.D., M.Sc., and Larry K.
Pickering, M.D., FIDSA, FPIDS, FAAP
• Hoch DE, et al. “Notes from the Field: Varicella
Outbreak Associated with Riding on a School Bus —
Muskegon County, Michigan, 2015.” MMWR Morb
Mortal Wkly Rep. 2016;65( 35):941–942, http://bit.
A parent residing in household A with five children
was diagnosed with herpes zoster (shingles) on Oct.
20, 2015, and was prescribed acyclovir. Four siblings
— 4-year-old twins, a 12-year-old and a 25-year-old —
subsequently developed a rash consistent with varicella
with onset ranging from Nov. 3-22, 2015.
On Dec. 3, 2015, the fifth sibling was sent home
from school due to rash consistent with varicella. The
8-year-old attended a different school than the other
children and rode a bus to and from school. The 8-year-
old was the first student on the bus in the morning and
the last to be dropped off in the afternoon.
Three additional cases of varicella were diagnosed
among children who rode the same bus as the 8-year-
old. A 7-year-old fully immunized child from house-
hold B developed a rash on Dec. 15, 2015, which was
confirmed as varicella by polymerase chain reaction
(PCR) from a cutaneous lesion. In addition, 7-year-
old and 5-year-old siblings living in household C had
onset of rash on Dec. 17, 2015, and Dec. 23, 2015,
respectively. They had not been immunized against var-
icella. A 17-month-old sibling in household C who
did not ride the bus and was not immunized against
varicella developed a rash on Dec. 28, 2015. Varicella
was confirmed in the 17-month-old and 5-year-old by
PCR testing from cutaneous lesions.
No other varicella cases were reported in the school
district that year. Varicella vaccine coverage in the
school was 96% for one dose and 95% for two doses,
which likely limited the extent of the outbreak. The
only interaction between cases from different households was sharing the same bus, suggesting that transmission occurred while they were on the bus.
School bus riding has been implicated as a factor in a
varicella outbreak in China. Varicella may be transmitted by physical contact with or inhalation of infectious
particles and has an incubation period of 10-21 days.
The close proximity of students in a relatively small,
enclosed space, such as a bus, may facilitate transmission of airborne diseases. Varicella may develop after
exposure to adults with herpes zoster (shingles), as occurred in this instance leading to nine varicella cases.
Contacts of people with varicella or shingles should be
evaluated for varicella immunity to determine the need for
post-exposure varicella vaccination, which may prevent
disease. The AAP Red Book recommends varicella vaccination for people 12 months of age and older without
evidence of pre-existing immunity up to five days after
varicella exposure, ideally within three days. A seven-day
course of acyclovir prophylaxis may be considered for
healthy children within the first seven days after exposure.
Varicella immunoglobulin (VariZIG) is recommended for the following groups after varicella exposure:
• immunocompromised children and pregnant
• newborn infants whose mothers develop varicella
within five days before or 48 hours after delivery,
• hospitalized preterm infants older than 28 weeks’
gestational age whose mothers are not immune to
• hospitalized preterm infants younger than 28
weeks’ gestational age regardless of maternal im-
Ideally, VariZIG should be given within 96 hours of
exposure but may be given up to 10 days after exposure.
Intravenous immunoglobulin may be used if varicel-la-specific immunoglobulin is unavailable. An algorithm for management of exposures to varicella-zoster
virus is available in Figure 3. 14 of the 2015 Red Book.
Varicella outbreak associated with riding on school bus
2015 AAP Red Book
Varicella lesions in a school-age child. Note the varying stages of development of the lesions (papules
and vesicles) and resolution (crusting). People are no
longer contagious once lesions have crusted.
2 doses of varicella vaccine highly effective
Which of the following statements is false?
A) Annual varicella incidence in the U.S. has declined by
85% since introduction of two-dose routine childhood
B) The largest decrease in annual varicella incidence after introduction of routine varicella childhood vaccination was observed among children 5-14 years of age.
C) It is not possible for a child to develop varicella after
exposure to an adult with herpes zoster (shingles)
D) Routine varicella vaccination is recommended at 12-
15 months and 4-6 years of age.
Reported varicella incidence by age group
o n 250
< 1 1-4 5-9 10-14 15-19 ≥ 20