What could possibly be the reason that Rotateq has not been found to cause intersusseption (sorry sp maybe) but Rotarix may possibly cause it according to those preliminary study results?
Good question and it is hard to say. Both are manufactured differently, Rotateq is a reassortant vaccine, meaning they took cow and human rotavirus strains and put parts of them together so that they elicit an immune response but not be pathogenic. Whereas Rotarix is a straight-up human, live, attenuated rotavirus so possibly can revert to wild-type? Here is the thing though, rotavirus infection has not been known to be associated with intussusception.
If they find that Rotarix does raise the risk to 4 in 100,000 as I read in a news article, will they pull the vaccine?
At NCKP, 16,627 doses of RRV-TV were administered to 9802 infants during December 1, 1998-June 10, 1999. Nine cases of intussusception among infants were identified with onset during that same period, all of which were radiographically or surgically confirmed. Three were among vaccinated children, with intervals of 3, 15, and 58 days following vaccination. The rate of intussusception among never-vaccinated children was 45 per 100,000 infant-years, and among children who had received RRV-TV was 125 per 100,000 infant-years (age-adjusted relative risk [RR]=1.9, 95% CI=0.5-7.7, p=0.39). The rate among children who had received RRV-TV during the preceding 3 weeks was 219 per 100,000 infant-years (age-adjusted RR=3.7, 95% CI=0.7-19, p=0.12). Among children who had received RRV-TV during the previous week, the rate was 314 per 100,000 infant-years (age-adjusted RR=5.7, 95% CI=0.7-50, p=0.11).
Bear in mind that this is expressed in person (infant) years so it would be the risk per year of intussusception with Rotashield. Here is a more straight-forward estimate: http://www.ncbi.nlm.nih.gov/pubmed/11207352
Assuming full implementation of a national program of vaccination with RRV-TV, we estimated that 1 case of intussusception attributable to the vaccine would occur for every 4670 to 9474 infants vaccinated.
I would suspect that this issue will be examined more closely, either another survey or mining the Vaccine Safety Datallink perhaps.