Before implementation of rotavirus vaccination in 2006, rotavirus caused 55,000-70,000 hospitalizations and 410,000 clinic visits annually in US children. This report examines the long-term impact of vaccine introduction on rotavirus detection and seasonality through comparison of pre (2000-2006) and post (2007-2015) vaccine seasons.
NREVSS is a passive laboratory system which collects results of weekly aggregate stool specimens and positive rotavirus detections. Seasons are defined as July of one year through June of the following year. To characterize changes in rotavirus detection, total and positive specimens for each season after vaccine introduction from 23-26 continuously reporting (≥26 weeks per season) laboratories were compared to median values for 2000-2006. Data from ~290 participating laboratories was used to determine pre and post-vaccine changes in season onset (first of two consecutive weeks during which ≥10% of specimens tested positive), duration, and peak. For season 2014-2015, data are available through March. Trend data are reported through March 2015, whereas season characteristics use complete seasons only.
Nationally, positive tests declined by 57.8%-89.9% in each post-vaccine season compared to 2000-2006. Pre-vaccine, median season onset occurred in epidemiological week 50, median peak activity in week 9 (43.1% positive) and seasons lasted a median of 26 weeks; post-vaccine seasons started later (weeks 1-9), had lower peak activity (10.9%-27.3%), and were shorter (0-18 weeks). A biennial pattern emerged, with alternating years of lower and greater activity (figure). All regions had similar reductions in positive tests. In the South, season onset and duration vacillated, with some post-vaccine seasons' onset and duration comparable to 2000-2006, whereas the remaining regions seasonality pattern was similar to each other.
Rotavirus vaccine substantially and sustainably reduced the burden and changed the epidemiology of rotavirus in US children. The biennial pattern observed may be explained by accumulating unvaccinated children over two successive seasons resulting in stronger rotavirus seasons every alternate year.
J. Tate, None
A. Haynes, None