New Whooping Cough Vaccine Safer, Study Says : Health: It is just as effective at preventing illness and causes far fewer side effects than the current treatment, a major clinical trial in Sweden finds.
A new whooping cough vaccine has been shown to be effective and much safer than existing vaccines in a major clinical trial in Sweden, the National Institutes of Health said Tuesday.
The currently used vaccine for whooping cough, formally known as pertussis, is part of the DPT vaccine routinely given to American children beginning at the age of 2 months. Although it is effective in preventing pertussis, there have been persistent reports that the current vaccine causes neurological damage in some children. Some countries, including Great Britain, Japan and Sweden have discontinued its use, and many parents refuse to allow their children to receive it.
In the trial, the new vaccine was given to 1,692 Swedish infants in three doses, at the ages of 3 months, 5 months and 12 months. The vaccine was about 71% effective in preventing pertussis, compared to about 80% for the current vaccine. Perhaps more important, the incidence of side effects, both mild and serious, was far below that reported with the current vaccine, said Dr. John Taranger of the University of Goteborg, who led the study.
“We really need to get a vaccine that has fewer side effects, and this seems to be a perfect solution to our problem,” said Dr. Lawrence Pickering, a pediatrician at the Center for Pediatric Research in Norfolk, Va.
Sharon Mates, president of North American Vaccine Inc., which manufactures the new vaccine, said the company plans to apply to the Food and Drug Administration early next year for marketing approval.
The pertussis vaccine has been used in the United States since the 1940s, commonly as part of the DPT vaccine, which also protects against diphtheria and tetanus. Children usually get the vaccine in a five-dose series, beginning at age 2 months and continuing at 4, 6 and 18 months, with a final dose between 4 and 6 years.
The current pertussis vaccine is called a whole-cell vaccine because it is made of killed pertussis bacteria. It contains not only a broad mix of cellular components of the bacteria, but also two different toxins that are produced by the microorganism. The pertussis endotoxin is thought responsible for the pain and fever associated with the vaccine, while the pertussis toxin--which causes most of the symptoms of whooping cough--is assumed to cause the more severe side effects.
Reactions to the vaccine usually occur within 48 hours and may include high fever (one out of 100 immunizations), persistent crying (one out of 100), seizures (one out of 1,750) and collapse episodes with limpness and lack of responsiveness (one out of 1,750).
Most side effects are reversible, but there have been persistent reports of permanent brain damage caused by the vaccine. Since the $80-million National Vaccine Injury Compensation program was established in 1988, 4,604 pertussis claims have been filed, according to the federal program’s records.
Because of their fears, many parents have refused to allow their children to receive DPT, leading to an increase in the incidence of the serious, sometimes fatal respiratory disorder. About 4,000 cases of pertussis occur each year in the United States.
In an effort to prevent these side effects, several groups of researchers have developed so-called acellular vaccines, which contain a mixture of proteins from cell walls of the bacteria. An acellular vaccine has been used successfully in Japan for several years and is approved in the United States for the fourth and fifth doses in the vaccination series. But the FDA has said that not enough evidence of safety and efficacy exists to justify using it in younger children, Pickering said.
The vaccine tested in Sweden is unique because instead of cell-wall proteins, it contains a modified form of the pertussis toxin. It was developed by molecular biologists Ron Sekura and John Robbins of the National Institute of Child Health and Human Development, who reasoned that a single protein would produce fewer side effects.
In addition to the vaccine, a placebo containing only the tetanus and diphtheria vaccines was given to 1,687 other infants in the double-blind Swedish study. The children were monitored for an average of 20 months after the third shot by a team of public health nurses who evaluated all coughing episodes. The use of a placebo was possible because most Swedish children do not receive a pertussis vaccine of any sort, despite an epidemic in that country.
During the trial, 240 of the children receiving the placebo developed pertussis, compared to only 72 who received the new vaccine. Although that is lower than the 80% efficacy of the current vaccine, said child health institute spokeswoman Michaela Richardson, the whole-cell vaccine has never been tested during an epidemic. The actual efficacies are probably about the same, she added.
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