ATLANTA — Rotavirus activity in the ongoing 2007–2008 season in the United States seems to have been delayed in onset by 2–4 months and to have diminished in magnitude by more than 50%, compared with the previous 15 seasons, coinciding with increasing rotavirus vaccine coverage.
The good news, from an interim analysis of data from the National Respiratory and Enteric Virus Surveillance System (NREVSS), was reported at a meeting of the Centers for Disease Control and Prevention's Advisory Committee on Immunization Practices by Cathy Panozzo of the epidemiology branch of the CDC's Division of Viral Diseases. The findings were reported on the same day in an early release of the CDC's Morbidity and Mortality Weekly Report (2008;57:697-700).
Before the 2007–2008 season, rotavirus disease followed a winter-spring pattern, with a median start in mid-November, median peak in mid-March, and median end in mid-June.
In 2008, the onset of rotavirus activity occurred in late February, peaked at the end of April, and continues to decline. The proportion of acute gastroenteritis patients aged younger than 3 years who had fecal specimen tests that were positive for rotavirus declined from a median of 41% for the previous 15 seasons: In 2008, 13.5% of tests were positive at week 12 of the season, and 17.8% were positive at the season's peak in April, said the MMWR.
The number of rotavirus tests done from Jan. 1 to May 3 in 2008, was 37% lower than that of the seven previous seasons, and the number of tests that were positive for rotavirus was lower by a median 78.5%.
Similarly, in a separate analysis of data from the prospective New Vaccine Surveillance Network of children aged younger than 3 years with acute gastroenteritis, 405 children were enrolled in the January-April 2006 period, and 481 in the same period of 2007, compared with 283 in 2008. Of those, the proportions with positive rotavirus tests were 51%, 54% and 6%, respectively, Ms. Panozzo said.
Data from eight sentinel U.S. sites suggest a mean 56% of infants aged 3 months received one dose of RotaTeq, and a mean of 33.7% infants aged 13 months received three doses. But because most children aged 2 years and older would have been too old to start the series when the vaccine was licensed in February 2006, the changes in rotavirus activity seem more pronounced than would be expected based on the protective effects of the vaccine alone. Thus, vaccinating some of the population may be conferring some degree of herd immunity, thereby reducing transmission to unvaccinated children, the CDC said.