The first thing to do is to contact your doctor. He or she will want to manage the immediate event, whether it is a seizure, a high fever, or just crying for several hours. The doctor might need to see your child in the office or the emergency room and, in severe cases, admit your child to the hospital.
After the immediate problem is stabilized, you and your doctor should discuss which vaccines were given and make a plan for future vaccinations. In some cases, a substitute vaccine will be suggested. For example, if a child is diagnosed with encephalopathy within seven days of receiving a DTaP vaccine, then that child should never receive a vaccination containing pertussis again. However, the DT vaccine will presumably be safe to finish the diphtheria and tetanus series.
Unfortunately, with combination vaccines and multiple vaccines given at once, it might be difficult to identify which vaccine was the likely culprit for the high fever. In that case, you might decide to give fewer vaccines at once for the next set of vaccines in the series. That way if you have a repeat episode of the high fever, then you can identify which vaccine might be to blame.
You should also recognize that the vaccine might not be the cause of the problem. Children have fevers and seizures all the time without any recent vaccinations. It could just be a coincidence that the two events occurred in the same few hours or days.
Finally, either you or your physician should report the event to the Vaccine Adverse Event Reporting System (VAERS). Information about VAERS can be found at http://vaers.hhs.gov/. You do not have to prove that the vaccine caused the problem. The researchers at VAERS simply want to know about any medical issues that occurred in close proximity to receiving vaccines. You can fill out the VAERS information online or print out a form and mail it to the organization.
Since 1990, the VAERS program has received well over a hundred thousand reports of medical events after vaccines. Over 85 percent of the reports are for mild and/or transient problems, such as fever, pain, or mild irritability. The remaining 15 percent include more serious experiences, such as being admitted to the hospital or requiring surgery.
If a pattern of events is seen with a given vaccine, then the FDA and CDC can act on the information. This is what occurred in the late 1990s with the rotavirus vaccine. Infants who recently received the rotavirus vaccine were suffering from an increased risk of intussusception, a bowel problem that usually requires surgery, at a higher rate than expected. After the first reports came in, the CDC launched a full investigation and subsequently recommended that the vaccine not be used in the United States.