6/29/2009

Work in progress, MMR information -- tracking down how the CDC figures out the number of adverse effects

http://www.cdc.gov/mmwr/preview/mmwrhtml/00046738.htm

"MEASLES PREVENTION
The following recommendations concerning adverse events associated with measles vaccination update those applicable sections in "Measles Prevention: Recommendations of the Immunization Practices Advisory Committee" (MMWR 1989; 38{No. S-9}), and they apply regardless of whether the vaccine is administered as a single antigen or as a component of measles-rubella (MR) or measles-mumps-rubella (MMR) vaccine. Information concerning adverse events associated with the mumps component of MMR vaccine is reviewed later in this document (see Mumps Prevention), and information concerning the rubella component is located in the previously published ACIP statement for rubella (18).

Side Effects and Adverse Reactions

More than 240 million doses of measles vaccine were distributed in the United States from 1963 through 1993. The vaccine has an excellent record of safety. From 5% to 15% of vaccinees may develop a temperature of greater than or equal to 103 F ( greater than or equal to 39.4 C) beginning 5-12 days after vaccination and usually lasting several days (19). Most persons with fever are otherwise asymptomatic. Transient rashes have been reported for approximately 5% of vaccinees. Central nervous system (CNS) conditions, including encephalitis and encephalopathy, have been reported with a frequency of less than one per million doses administered. The incidence of encephalitis or encephalopathy after measles vaccination of healthy children is lower than the observed incidence of encephalitis of unknown etiology. This finding suggests that the reported severe neurologic disorders temporally associated with measles vaccination were not caused by the vaccine. These adverse events should be anticipated only in susceptible vaccinees and do not appear to be age-related. After revaccination, most reactions should be expected to occur only among the small proportion of persons who failed to respond to the first dose.

Personal and Family History of Convulsions

As with the administration of any agent that can produce fever, some children may have a febrile seizure. Although children with a personal or family history of seizures are at increased risk for developing idiopathic epilepsy, febrile seizures following vaccinations do not in themselves increase the probability of subsequent epilepsy or other neurologic disorders. Most convulsions following measles vaccination are simple febrile seizures, and they affect children without known risk factors.

An increased risk of these convulsions may occur among children with a prior history of convulsions or those with a history of convulsions in first-degree family members (i.e., siblings or parents) (20). Although the precise risk cannot be determined, it appears to be low.
In developing vaccination recommendations for these children, ACIP considered a number of factors, including risks from measles disease, the large proportion (5%-7%) of children with a personal or family history of convulsions, and the fact that convulsions following measles vaccine are uncommon. Studies conducted to date have not established an association between MMR vaccination and the development of a residual seizure disorder (5). ACIP concluded that the benefits of vaccinating these children greatly outweigh the risks. They should be vaccinated just as children without such histories.

Because the period for developing vaccine-induced fever occurs approximately 5-12 days after vaccination, prevention of febrile seizures is difficult. Prophylaxis with antipyretics has been suggested as one alternative, but these agents may not be effective if given after the onset of fever. To be effective, such agents would have to be initiated before the expected onset of fever and continued for 5-7 days. However, parents should be alert to the occurrence of fever after vaccination and should treat their children appropriately.

Children who are being treated with anticonvulsants should continue to take them after measles vaccination. Because protective levels of most currently available anticonvulsant drugs (e.g., phenobarbital) are not achieved for some time after therapy is initiated, prophylactic use of these drugs does not seem feasible.

The parents of children who have either a personal or family history of seizures should be advised of the small increased risk of seizures following measles vaccination. In particular, they should be told in advance what to do in the unlikely event that a seizure occurs. The permanent medical record should document that the small risk of postimmunization seizures and the benefits of vaccination have been discussed."

"Allergic Reactions
Hypersensitivity reactions rarely occur after the administration of MMR or any of its component vaccines. Most of these reactions are minor and consist of a wheal and flare or urticaria at the injection site. Immediate, anaphylactic reactions to MMR or its component vaccines are extremely rare. Although greater than 70 million doses of MMR vaccine have been distributed in the United States since VAERS was implemented in 1990, only 33 cases of anaphylactic reactions that occurred after MMR vaccination have been reported. Furthermore, only 11 of these cases a) occurred immediately after vaccination and b) occurred in persons who had symptoms consistent with anaphylaxis (CDC, unpublished data). "


There's much more information there, Craig, but it looks like they're going off of unpublished data and VAERS. I'll see if I can find any studies that compared VAERS data to survey data. Tomorrow. :-)

Update: 0730 06/30:

It looks like they are collecting the unpublished data this way:

"Rapid Cycle Analysis (RCA)

Recent events in the United States highlight the importance of setting up computerized reporting systems to detect adverse events as they happen. In 2005, the Vaccine Safety Datalink (VSD) Project team launched an active surveillance system called Rapid Cycle Analysis (RCA). Its goal is to monitor adverse events following vaccination (possible side effects) in near real time, so the public can be informed quickly of possible risks. The VSD Project team uses RCA to monitor newly licensed vaccines and new vaccine recommendations.
RCA data come from participating managed care organizations that include more than 8.8 million people annually, representing nearly 3% of the United States population. The RCA data contain no personal identifiers."

http://www.cdc.gov/vaccinesafety/vsd/rca.htm

I haven't had the chance to read the whole page yet, but wanted to get it posted and up for you, Craig, and any other readers interested. I'll continue digging and reading when I get back this morning. It's another running around day dropping and picking up kids. :-)

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