Rotavirus infection is the leading

Rotavirus infection is the leading cause of severe gastroenteritis
among infants and young children worldwide (1,2).
Before the introduction of rotavirus vaccine in the United
States in 2006, rotavirus infection caused significant morbidity
among U.S. children, with an estimated 55,000–70,000
hospitalizations and 410,000 clinic visits annually (3). The
disease showed a characteristic winter-spring seasonality and
geographic pattern, with annual seasonal activity beginning
in the West during December-January, extending across the
country, and ending in the Northeast during April-May (4). To
characterize changes in rotavirus disease trends and seasonality
following introduction of rotavirus vaccines in the United
States, CDC compared data from CDC’s National Respiratory
and Enteric Virus Surveillance System (NREVSS), a passive
laboratory reporting system, for prevaccine (2000–2006) and
postvaccine (2007–2014) years. National declines in rotavirus
detection were noted, ranging from 57.8%–89.9% in each of
the 7 postvaccine years compared with all 7 prevaccine years
combined. A biennial pattern of rotavirus activity emerged in
the postvaccine era, with years of low activity and highly erratic
seasonality alternating with years of moderately increased activity
and seasonality similar to that seen in the prevaccine era.
These results demonstrate the substantial and sustained effect
of rotavirus vaccine in reducing the circulation and changing
the epidemiology of rotavirus among U.S. children.
NREVSS is a national laboratory-based passive reporting
system for respiratory and enteric viruses, including rotavirus.
Participating laboratories report weekly data to CDC, including
the total number of stool samples tested for rotavirus by enzyme
immunoassay and the number of specimens that tested positive.
Annually, 75 to 90 laboratories report rotavirus testing data to
NREVSS. A reporting year is defined as the period from July
(epidemiologic week 27) to June (epidemiologic week 26) of the
following year, beginning in July 2000. Rotavirus season onset isdefined as the first of 2 consecutive weeks where 10% or more
of specimens test positive for rotavirus. Similarly, season offset
is defined as the last of 2 consecutive weeks where 10% or more
of samples test positive. Peak season intensity is defined as the
week with the highest proportion of tests positive for rotavirus.
For analysis of season duration and peak intensity, data from
all participating laboratories were included. The proportion of
samples that tested positive for rotavirus and the mean decrease
from the prevaccine years are reported for these data. Analyses
of trends in disease were restricted to the 23 laboratories that
consistently reported at least 26 weeks of data for each reporting
year from July 2000 through June 2014. For this analysis, data
are aggregated by week and reported as a 3-week moving average
of total number of tests and rotavirus positive tests performed