I note that nowhere in the quoted text does it discuss negative effects. In fact, the very next sentences say:

"In 1998, the National Cancer Institute undertook a large study, using cancer case information from the institute's SEER database. The published findings from the study revealed no increased incidence of cancer in persons who may have received vaccine containing SV40."

And beyond that, a full discussion requires comparison of negative side effects of the vaccine vs side effects of the original virus, and the rate of such effects. We know, factually, that there are often some side effects from vaccines. We also know, factually, that often the vaccine side effects are either of less severity and/or less frequency than the effects of catching the original virus. In other words, statistically, most of the time you're better off tempting fate with the vaccine than with the virus.