Small Shots, Big Fears
Recent research has debunked many fears that vaccines can cause certain childhood disorders:
In 1998 a British doctor urged a follow-up of his earlier observation that the MMR vaccine might, in rare cases, cause such behavioral problems as autism by triggering an intestinal disorder like Crohn's disease. He had based his conjecture on a small group of cases -- 12 children. Since then, several large-scale investigations in the U.S., England, and Finland showed that neither Crohn's disease nor autism occurs more often following immunization.
In children 6 months to 5 years old, a fever can trigger brief seizures marked by jerking or stiffness. Two vaccines -- the MMR and the diphtheria-tetanus-pertussis (DTP) -- commonly cause fever and thus, in a small number of cases, seizures. These fever-related incidents occur in 1 in 3,000 children vaccinated against MMR and 1 in 1,700 kids inoculated with the old, whole-cell DTP vaccine. (The rate is markedly lower with the newer, "acellular" DTaP vaccine: 1 in 14,000 children.)
In the vast majority of cases, convulsions caused by fever in young children do no lasting harm -- although they can be frightening to parents. In about 1 in a million cases, though, these seizures are followed by epilepsy, coma, or mental impairment. In such instances, some researchers suspect, the fever simply unmasked an underlying condition: If the vaccine-related fever hadn't triggered the onset of the disorder, another fever would have done so. There hasn't been enough research to know for sure whether this is true, and in rare instances, seizures are not fever induced.
Anti-vaccine groups also claimed that whole-cell DTP increased the risk of SIDS, but large studies have found that immunized infants actually have a slightly lower risk.
In 1998 France suspended hepatitis B immunization requirements among children following isolated reports that tied the vaccine to multiple sclerosis. Soon afterward, drug companies funded several international studies, and no evidence was found to link the two.
In the 1990s one hypothesis explaining the rise in the rates of allergic diseases, such as hay fever, asthma, and eczema, was that better hygiene was shielding children from the germs they needed to "educate" their immune system to distinguish harmless substances like pollen and dust from more harmful bacteria and viruses. Some scientists wondered whether vaccines might contribute to that by preventing kids from contracting "normal" childhood diseases. A recent study of immunization rates at 91 medical centers in 38 countries put such concerns to rest, showing no association between vaccination and the incidence of allergic diseases in children ages 6 to 7. In a separate study of children ages 13 to 14, those with the highest immunization rates actually had lower rates of allergic conditions.
In 1997 an immunologist theorized that the timing of the flu vaccine might have an influence on the occurrence of Type 1 diabetes. But a 2001 study done by the Centers for Disease Control and Prevention (CDC) that compared infants who developed diabetes with those who did not found no link between the time the vaccine was given and the disease.
One of the charges leveled most frequently by anti-vaccine activists is that too many immunizations can overwhelm a young child's developing immune system. This theory is currently being investigated by the Immunization Safety Review Committee, created by the CDC and the Institute of Medicine of the National Academies of Science. But pediatric immunologist Richard Johnston, M.D., at the University of Colorado School of Medicine says that taken together, the purified antigens (compounds that stimulate an immune response, which protects against the real disease) in all of the recommended childhood vaccines represent a mere drop in the ocean compared to what small children are exposed to in their daily lives. And many studies have found that when several vaccines are combined into one shot -- standard practice -- no major adverse side effects have been detected.