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2/28/2001

Negative Vaccine Studies Counter Safety Concerns

Kate Traynor

The results of new epidemiological studies testing for links between childhood immunization and chronic disease may help health care providers reassure parents about the benefits of immunization.

In a study reported in the Feb. 17 issue of BMJ, researchers found no link between the incidence of autism and childhood immunization with the measles, mumps, and rubella (MMR) vaccine. An unrelated report in the Feb. 1 New England Journal of Medicine (NEJM) similarly found no association between hepatitis B vaccination and the onset of multiple sclerosis.

To examine the possibility of a relationship between multiple sclerosis and the hepatitis B vaccine, researchers collected data from two ongoing studies: the Nurses’ Health Study, which began in 1976, and the Nurses’ Health Study II, which began in 1989. A total of 301 of the approximately 238,000 study participants were diagnosed with multiple sclerosis since the early 1990s, when queries about this disease were first included in study questionnaires.

The researchers examined data from the 192 nurses who had multiple sclerosis and whose hepatitis B vaccination status could be confirmed with insurance records. These nurses were matched to 645 nurses who did not have multiple sclerosis.

According to the researchers, there was no evidence that nurses vaccinated against hepatitis B had an increased risk of multiple sclerosis in the ensuing years. But when the researchers relied on the nurses' self-reported vaccination dates instead of insurance records, there did seem to be an increased risk, indicating that recall bias plays a role in this type of research.

The study on autism examined data from the United Kingdom general practice research database and identified children 12 years or younger who were diagnosed with the disorder between 1988 and 1999. Although the incidence of autism increased dramatically during these 12 years, the percentage of children who received the MMR vaccine remained constant at over 95 percent each year. The research team concluded that the MMR vaccine, which was introduced in the United Kingdom in 1988, did not contribute to the increased incidence of autism.

The importance of disseminating the results of "negative" studies, such as the two recent ones, was underscored by two Vanderbilt University physicians in a Feb. 1 NEJM editorial. They said that researchers should "acknowledge the force of the consumer movement" and determine which concerns merit investigation into a possible causal relation between vaccine administration and adverse events.

Parents' misconceptions about the risks and benefits of childhood vaccines were highlighted in a study reported in the November 2000 issue of Pediatrics. This study found that 25 percent of parents surveyed believed that immunizations can weaken their childrens’ immune systems. Twenty-three percent of the parents believed that their children were immunized more often than was good for them, and nearly 40 percent said that immunizations are needed only to prevent "serious diseases."

Despite the overall safety of vaccines, there are legitimate concerns. Wyeth-Ayerst Inc.’s Rotashield vaccine, for example, was withdrawn from the market in 1999, just over a year after the product was first sold in the United States. Rotashield use was halted because of what the Centers for Disease Control and Prevention (CDC) termed a "strong association" between vaccination and subsequent bowel obstruction in young infants.

Physicians have been legally required to discuss with parents the risks and benefits of childhood vaccination since 1986, when the National Childhood Vaccine Injury Act went into effect. Despite this legal requirement, a study reported in the February issue of Pediatrics found that 40 percent of physicians’ offices do not mention vaccine risks to parents.

About a quarter of the physicians surveyed said that discussion of vaccine risks would unnecessarily alarm parents, and about 15 percent said that parents do not understand discussions of risk. Fewer than half of the physicians initiated discussions with parents about contraindications to vaccination, and about 12 percent informed parents about the National Vaccine Injury Compensation Program.

Approximately 40 percent of the physicians surveyed admitted to not giving vaccinees the CDC Vaccine Information Statement (VIS) with each vaccine dose, and about 30 percent apparently do not give out the VIS at all. The 1986 law requires distribution of the appropriate VIS with each vaccine dose.

Good News About Prevnar

Finnish researchers reported in the Feb. 8 NEJM that Prevnar, Wyeth-Ayerst's seven-valent pneumococcal conjugate vaccine, protects against acute otitis media in children two years of age or younger. The incidence of otitis media due to pneumococcal serotypes represented in the vaccine was 57 percent lower among vaccinated children than in unvaccinated children. The overall incidence of acute otitis media was 6 percent lower in vaccinees than in children who did not receive the vaccine.