They found that there were 6 cases of intussusception after 207,955 doses of one kind of vaccine, whereas only 0.72 cases would have been expected from the 2001 – 2005 figures. Therefore the risk of intussusception increased 8.4 times after immunization.
The authors found no such increase after the use of another type of vaccine, with 8 cases after 1,301,801 doses administered instead of the expected 7.11. This difference was too small to be statistically significant; it might easily have arisen by chance. However, another study of this vaccine, from Australia rather than the United States, suggested that the size of the risk with this vaccine was similar to that of the other.
Therefore, on the balance of probability, immunization against rotavirus does cause intussusception in infants and is therefore not entirely harmless. To that extent the conspiracy theorists are correct. But good in medicine seldom comes without the possibility of harm (the reverse, alas, is not true), and if doctors never prescribed anything that might do harm as well as good they would not prescribe anything at all. The good must always be weighed against the harm and in this case the balance seems overwhelmingly on the side of the good. The very fact that such huge numbers of cases have to be treated to reveal any harm at all is an indication that, in numerical terms at least, it cannot be very great.