http://www2.epediatricnews.com/scripts/om.dll/serve?action=searchDB&searchDBfor=art&artType=full&id=aqp030370707b

Note:  But how many children do these .65 per million vaccinations represent? - SM

July 2003 • Volume 37 • Number 7

News

Events low, but impossible to predict
Vaccine-Associated Anaphylaxis Risk Calculated at 0.65 per Million

Timothy F. Kirn

SEATTLE — Pediatricians and other vaccine providers should be prepared to manage anaphylactic shock, Kari J. Bohlke, Sc.D., said in a poster presentation at the annual meeting of the Pediatric Academic Societies.

The risk of anaphylaxis following vaccination appears to be about 0.65 per million vaccinations, said Dr. Bohlke, a researcher in the department of pediatrics at the University of Washington, Seattle.

To come to that estimate, Dr. Bohlke and her colleagues reviewed records from four Western health maintenance organizations enrolled in the federal government's Vaccine Safety Datalink Project. Among the approximately 7 million doses of vaccine given by the HMOs between 1991 and 1997, the researchers identified 5 cases of potentially vaccine-associated anaphylaxis.

Previously there have been no estimates on how often vaccine-associated anaphylaxis can occur in clinical practice, although it has been accepted that most of the vaccines implicated in this survey can cause anaphylaxis, she said.

All but one of the patients received multiple vaccines at the time of their pertinent visit. That patient received only the MMR vaccine. The other vaccines implicated in the study were hepatitis B (2 cases), diphtheria-tetanus (1 case), diphtheria-tetanus-pertussis (3 cases), Haemophilus influenzae type b (3 cases), and the oral polio vaccine (3 cases).

Computing the rate for each vaccine—given the numbers of each vaccine delivered, and based on the assumption that each and every vaccine given to a particular patient who had a reaction was the cause—the researchers estimated that the vaccine with the highest rate of anaphylactic reactions was the diphtheria-tetanus vaccine, at about 21 per million doses. The next riskiest vaccine according to their estimates was the MMR, with a rate of 3.5 per million doses, followed by the DTP-Hib, with a rate of 3.4 per million doses.

All of their estimates may be high, however, including their overall rate, she said. One of the cases they included was an apparent anaphylactic reaction that did not occur until a day after that particular adolescent was vaccinated. It was included because patient records noted it as possibly associated.

Regarding actual incidents, all five cases were eventually treated in an emergency department or hospital. Three were received epinephrine and parenteral antihistamines and/or steroids. None died.

The most important message provided by the study is that it shows it is impossible to predict when these events will occur, which is why it behooves vaccine providers to be prepared, Dr. Bohlke said in an interview.