WASHINGTON — Two years after approval of an oral rotavirus vaccine, pediatric rotavirus cases and hospitalizations in U.S. hospitals have decreased dramatically, according to two national studies as well as a number of local analyses.
That decline is present in nonvaccinated age groups, likely because of reduced overall circulation and transmission of the virus in children of all ages, say researchers.
At the joint annual Interscience Conference on Antimicrobial Agents and Chemotherapy and annual meeting of the Infectious Diseases Society of America, T. Christopher Mast, Ph.D., associate director of the department of epidemiology at Merck & Co. (maker of the oral RotaTeq vaccine), reported on 33,135 infants who received all three vaccine doses between Jan. 1, 2007, and April 30, 2007, and 27,954 infants who had received multiple vaccines—but not the rotavirus vaccine—during that time.
The nonrandomized, claims-based observational study data showed a 100% reduction in combined hospital and emergency department (ED) visits in the vaccinated group during the 2007 and 2008 seasons (from January through May). Physician visits were cut by 96% in the vaccinated group, compared with the unvaccinated group. Associated medical costs resulting from hospitalization and ED visits were cut by $12,000 in the vaccinated group, compared with those in the unvaccinated group.
In a second presentation, Dr. Jay Lieberman, medical director for infectious disease for Quest Diagnostics Inc., reported on national rotavirus testing data from Quest's information data warehouse. In the three seasons before licensure of the vaccine (December through June of 2003–2004, 2004–2005, and 2005–2006), 27,625 rotavirus tests on average were performed during the peak disease season, of which 7,162 (26%) were positive. In contrast, in the most recent peak season (from December 2007 through June 2008), 1,703 (8%) of the 21,873 tests performed were found to be positive—a highly significant reduction.
Moreover, “the number of positive tests and the positivity rate declined after vaccine licensure in every age group, including those [aged] 2–5 years, who are unlikely to have been vaccinated,” he wrote in a poster, evidencing herd immunity.
The decline in rotavirus also was shown in several regional studies on the efficacy of RotaTeq. In one of at least eight such posters, Dr. Irini Daskalaki of Drexel University in Philadelphia found a decrease in hospitalizations at St. Christopher's Hospital for Children (also in Philadelphia) ranging from 20% to 94% among different age groups at 1 full year after vaccine implementation. And, as in Dr. Lieberman's study, prominent decreases were seen even in unvaccinated age groups.
Neither Dr. Lieberman nor Dr. Daskalaki disclosed any conflicts of interest.
Data from the U.S. VAERS (Vaccine Adverse Event Reporting System) also presented in a poster at the meeting, confirmed the results of prelicensure studies of the vaccine's safety: Of 21,093,180 doses administered between Feb. 1, 2006, and Aug. 30, 2008, according to Merck, 2,600 adverse event reports were filed with VAERS, 683 (26%) of which were serious. Of the serious reports, 328 (48%) involved cases of intussusception, a rate that was not considered sufficient to cause concern. The other adverse events were vomiting and diarrhea. There was one death.
RotaTeq—a live, oral, human-bovine reassortment rotavirus vaccine—was licensed in February 2006, and routine vaccination was recommended by the Centers for Disease Control's Advisory Committee on Immunization Practices (ACIP) later that year. It is administered in three doses before 32 weeks of age. It is the second rotavirus vaccine to be approved in the United States. The first, RotaShield, was removed from the market in 1999 because of a detected increase in intussusceptions.
A two-dose oral rotavirus vaccine, Rotarix (from GlaxoSmithKline) also was approved by the Food and Drug Administration in April of this year.