Top vaccine controversies

MMR (Measles-mumps-rubella)

Fear: The vaccine can cause autism.

Origin: In a 1998 study of 12 British children with intestinal disorders, eight children developed autism shortly after receiving the MMR shot.

Research: A study of more than 500,000 Danish children found no connection. The U.S. Institute of Medicine (IOM), an agency chartered by Congress to provide the government health advice, reviewed the research and concluded that for the general population, there was no link. But the agency did not rule out the possibility that in rare cases, the vaccine may contribute to the disorder. It called for more research.

DPT/DTaP (Diphtheria, tetanus and pertussis/whooping cough)

Fear: The vaccine leads to brain damage.

Origin: A study of 1,000 British children with brain illnesses connected the DPT vaccine to brain inflammation.

Research: The IOM reviewed 10-year follow-up data on the children and concluded the vaccine could cause seizure disorders and brain damage in rare cases — up to one in 100,000 children. DTaP, a safer version of the old DPT vaccine, is thought to cause fewer cases.

Hepatitis B

Fear: The vaccine can cause multiple sclerosis (MS).

Origin: Individual reports of adults who developed MS and other autoimmune diseases after receiving the shot prompted fears of a link. This dovetailed with concerns about rising MS rates in some communities.

Research: Most population studies do not support an association. The IOM said biological links are feasible, but evidence showed no connection to MS. The agency concluded there wasn't enough research to address other autoimmune diseases.

Mercury in vaccines

Fear: Vaccines containing mercury have contributed to a rise in autism, attention deficit hyperactivity disorder and learning disabilities.

Origin: Mercury is known to impair brain development in children, yet until 2001 it was used in thimerosal, a preservative in three childhood vaccines: hepatitis B, haemophilus type b and DTP.

Research: In 1999, the Food and Drug Administration added up the cumulative mercury exposure from these vaccines and found the levels surpassed the Environmental Protection Agency's safety level. But the government contends there's no proof of harm to children. But since 2001, childhood vaccines have been made without significant amounts of thimerosal. Some manufacturers still make an influenza vaccine with the preservative.

Polio

Fear: The vaccine causes polio.

Origin: The oral vaccine used from 1960 contained a live virus that did cause polio.

Research: Beginning in 1979, the only U.S. cases of polio — about eight a year — were caused by the vaccine. In 1999, the Centers for Disease Control and Prevention voted to switch to the injectable form of the vaccine, which cannot cause polio.

Sources: IOM, Centers for Disease Control and Prevention, National Vaccine Information Center.