Unusual US Rotavirus Season May Be due to Newly Introduced Vaccine

CDC has issued an interim report describing marked changes in rotavirus activity in the ongoing 2007–08 US rotavirus season. The report indicates that rotavirus activity started considerably later and was much less extensive compared with activity in previous years. These changes coincide with increasing use of rotavirus vaccine among infants.

Rotavirus is the leading cause of severe diarrhea (often accompanied by vomiting, fever, and dehydration) in infants and young children. Each year in the United States, rotavirus disease causes about 410,000 physician office visits, 205,000–272,000 emergency department visits, 55,000–70,000 hospitalizations, and 20–60 deaths among children less than 5 years of age. Worldwide, rotavirus causes approximately 1,600 deaths each day among children less than 5 years of age.

The CDC report, "Interim Report: Delayed Onset and Diminished Rotavirus Activity — United States, November 2007 – May 2008," appears in an early-release edition of CDC's Morbidity and Mortality Weekly Report. According to the report, data from around the United States indicate that during the ongoing 2008 season, rotavirus activity started 2–4 months later than usual and never approached peak activity levels seen during any of the last 15 rotavirus seasons. Looking at comparable time periods in past rotavirus seasons, it was found that during this season, the number of laboratory tests performed for rotavirus was 37% lower than usual and the percent of all tests conducted for gastroenteritis that were positive for rotavirus was 79% lower than usual. A network of hospitals that are closely following rotavirus activity reported that severe outcomes of rotavirus disease (hospitalizations, emergency department visits, physician visits) were reduced by about 90%–95%. These changes appear to be greater than expected based on direct protective effects of vaccination alone. This raises the possibility that the current level of vaccination among infants may be decreasing spread of rotavirus to unvaccinated individuals in the community.

For More Information

• For more information about the findings, read Interim Report: Delayed Onset and Diminished Rotavirus Activity — United States, November 2007 – May 2008, MMWR 25 June 2008/57 (Early Release);1–4.
• For answers to questions you may have about the interim report, read the related Questions and Answers.
• To learn more about rotavirus, visit CDC's Rotavirus Web page.
• To learn more about the rotavirus vaccine, visit CDC's Rotavirus Vaccination Web page.