TURSDAY June 26, 2008 (foodconsumer.org) -- The Centers for Disease Control and Prevention on Wednesday June 25 released a report saying that the onset of rotavirus activity in the ongoing 2007-2008 season seems to have been delayed and the activity appears to be the least severe than any previous seasons, an observation that the agency suggests is due to the newly introduced rotavirus vaccine.

The report published in the agency's publication known as Morbidity and Mortality Weekly Report (MMWR) says that data from around the United States indicated that during the ongoing season, rotavirus activity was delayed by about three months, the latest compared to any previous seasons in the past 15 years since the agency started monitoring the virus.

In this season, rotavirus began to be active at the end of February, 2008 instead of last November, the usual onset time and the reason peaked at the end of April, 2008 instead of March, the usual peak time, the CDC says in a statement.

Rotavirus is the leading cause for severe gastroenteritis leading to diarrhea and vomiting in infants and young children.   The virus causes 410,000 physician office visits, 205,000-272,000 emergency department visits and 55,000-70,000 hospitalizations, but it rarely causes deaths in children younger than 5 in the United States (20 to 60 deaths each year).

The CDC says since the introduction of Merck's rotavirus vaccine RotaTeq, hospitalizations, emergency department visits, and physician visits were substantially reduced at selected medical centers conducting prospective rotavirus surveillance by the government.

The number of lab tests performed for rotavirus from Jan. 1 to May 3, 2008 was reduced by 37 percent compared to the usual. Among the tests, the positive rate for gastroenteritis was 79 percent lower than usual.

RotaTeq, manufactured by Merck & Co. Inc. was approved in 2006 and recommended for routine immunization of U.S. infants at 2, 4 and 6 months of age.

The CDC cites trial data in its press release saying the live oral vaccine is able to prevent 74 percent of all rotavirus cases, about 98 percent of severe cases and about 96 percent of hospitalizations caused by rotavirus.

"The changes appear to be greater than expected based on the protective effects of the vaccine alone," said Dr. Anne Schuchat, director of the National Center for Immunization and Respiratory Diseases at CDC.

"It is also possible that current levels of vaccination may be helping to decrease the spread of rotavirus to unvaccinated individuals in the community. Ongoing monitoring is needed to confirm the impact of vaccination this year and to monitor the impact of the vaccine on rotavirus disease and its epidemiology over time."

The new surveillance data did not come from all county health departments.   Rather they were reported weekly from the New Vaccine Surveillance Network, which tracks the virus in three counties and the tests were performed by the National Respiratory and Enteric Virus Surveillance System (NREVSS), the Los Angeles Times reports.

There are some limitations to the surveillance data, editors of MMWR say in their editorial note included in the report.   The following is cited in verbatim from the report.

The findings in this report are subject to at least five limitations. First, the 2007--08 rotavirus season is still ongoing, and further information is needed to evaluate rotavirus activity fully. Second, although most laboratories submit reports to NREVSS within 2 weeks of testing, delays in reporting might have some effect on these preliminary data. Third, testing for rotavirus is not part of routine clinical practice and is conducted at the discretion of the physician and based on institutional policies. Changes in testing practices might impact these findings; however, such changes would be unlikely to explain the large decline in positive test results in 2008, particularly given the consistency of this decline across participating laboratories. Fourth, because NREVSS is a purely laboratory-based surveillance system, patient-level information is not available and NREVSS might receive more than one result for a given patient. However, any contribution of this to the results likely would be small. Finally, the counties where NVSN conducts active surveillance might not be representative of the entire U.S. population; however, the findings from NREVSS support very similar interpretation.

The rotavirus vaccine is not free of adverse effects. The Food and Drug Administration published RotaTeq™ Questions and Answers giving the public some ideas what kinds of side effects the vaccine may cause cited in verbatim as follows.

The following were reported more often in infants who received RotaTeq™, when compared to those who received placebo; diarrhea (24.1% in vaccine recipients vs 21.3% in those receiving placebo), vomiting (15.2% in vaccine recipients vs 13.6% in those receiving placebo), ear infection (14.5% in vaccine recipients vs 13.0% in those receiving placebo), runny nose and sore throat (6.9% in vaccine recipients vs 5.8% in those receiving placebo), wheezing and coughing (1.1% in vaccine recipients vs 0.7% in those receiving placebo).

The vaccine is designed to prevent gastroenteritis, which causes diarrhea and vomiting. It is ironic that those who received the vaccine seemed to have slightly high incidents of these symptoms compared to those who did not.

Rotavirus is transmitted by the facal-oral route via contact with contaminated hands, surfaces and objects and possibly by the respiratory route. The virus is highly contagious. The faces of an infected person can contain more than 10 trillion infectious virus particles per gram, but only 10 to 100 of them are enough to cause an infection in another person, according to Wikipedia.   To prevent an infant from getting the virus, family members should practice good hygiene and wash their hands before they walk out of the bathroom.