The Supreme Court on Tuesday shielded the nation's vaccine makers from being sued by parents who say their children suffered severe side effects from the drugs.
By a 6-2 vote, the court  upheld a federal law that offers compensation  to these victims through a special tribunal but  closes the courthouse door to lawsuits.
The majority said that Congress found such a system necessary to ensure  that vaccines remain readily available, and that federal regulators are  in the best position to decide whether vaccines are safe and properly  designed.
The National Childhood Vaccine Injury Act of 1986 "reflects a sensible  choice to leave complex epidemiological judgments about vaccine design  to the FDA and the National Vaccine Program rather than juries," Justice  Antonin Scalia wrote, referring to the Food and Drug Administration.
Justices Sonia Sotomayor and Ruth Bader Ginsburg dissented, saying the  threat of lawsuits provides an incentive for vaccine manufacturers to  constantly monitor and improve their products.
The decision "leaves a regulatory vacuum in which no one - neither the  FDA nor any other federal agency, nor state and federal juries - ensures  that vaccine manufacturers adequately take account of scientific and  technological advancements," Sotomayor wrote.
The case was brought by Russell and Robalee Bruesewitz on behalf of  their daughter Hannah, 18. Hannah began to have seizures as an infant  after receiving the third of five scheduled doses of Wyeth's Tri-Immunol  diphtheria-pertussis-tetanus vaccine. The company, now owned by Pfizer,  has taken the drug off the market. 
The 1986 federal law said that all such claims must first go to a  special tribunal commonly called the "Vaccine Court." The program has  awarded nearly $2 billion for vaccine-injury claims in nearly 2,500  cases since 1989. It is funded by a tax on immunizations. 
But the tribunal ruled against the Bruesewitzes, saying they had not  proved that the vaccine harmed Hannah, who will need life-long care.
The couple then sued under Pennsylvania tort law. The company had the  case moved to federal court, and judges have consistently ruled that the  suit cannot proceed, because federal law prohibits claims against  "design defects" in vaccines.
The justices at oral argument debated ambiguous wording in the federal  law. It says that no vaccine maker can be held liable for death or  injuries arising from "side effects that were unavoidable even though  the vaccine was properly prepared and was accompanied by proper  directions and warnings."
Scalia said the word "unavoidable" would be meaningless "if a  manufacturer could be held liable for failure to use a different  design."
Sotomayor read the language to mean the opposite, and said "text,  structure and legislative history compel the conclusion that Congress  intended to leave the courthouse doors open for children who have  suffered severe injuries from defectively designed vaccines."
The case is 
Bruesewitz v. Wyeth.