For help, WebMD turned to the CDC's Frank DeStefano, MD, MPH, director of its immunization safety office.
Are there dangerous side effects or reactions to childhood vaccines?
Fortunately, dangerous side effects or reactions to vaccines are few and rare.
Probably the main one is anaphylaxis, a severe allergic reaction. But like I said, it’s rare. It occurs on the order of one per several hundred thousand to one per million vaccinations.
The other condition is encephalopathy, and that is even more rare, primarily reported with the [old form] of pertussis [vaccine]. But that hasn't been used in the United States for more than 10 years.
In terms of reactions that have the potential to kill you or result in lasting disability, they are very rare.
We hear about adverse events; is that the same as a dangerous reaction?
An adverse event following immunization can be any adverse health condition that occurs after the vaccination. It doesn't necessarily have to be caused by the vaccine.
Can you give an example?
Vaccines are given to millions of people every year. A lot of people will have adverse health events that occur just coincidentally after vaccination. An adverse event of pregnancy is miscarriage, those occur in 10% or more of pregnancies. Often if a woman has a vaccine and then within several weeks has a miscarriage, there is the temptation to say the miscarriage was caused by the vaccine.
What does the CDC do when it gets a report that a vaccine has caused a serious side effect?
It depends on the nature of the condition. There is a routine reporting system; physicians can file reports. What we do depends on whether it is a known adverse reaction to a vaccine or whether it's not known.
We get as detailed information on the case as possible.
If it's a known adverse vaccine reaction, usually questions arise about the clinical management [for the patient]. For example, febrile seizures. This is a known adverse reaction after MMR [measles, mumps, rubella] vaccine, [occurring in] about 1 in 2,500 vaccinations.