(dailyRx News) Numbers of whooping cough cases have increased dramatically in the past several years. The biggest reason appears to be related to the newer vaccine for the disease.
A recent study found that the current vaccine used for whooping cough, or pertussis, is less effective than the previous one.
The DTaP vaccine protects against pertussis, but it only started being used in the 1990s. Before then, a different shot called DTP was used before it was discontinued due to safety concerns.
The newer shot may safer than the old shot, but it does not appear to protect as well against pertussis.
The study, led by Nicola P. Klein, MD, PhD, of the Northern California Kaiser Permanente Vaccine Study Center in Oakland, compared the effectiveness of two different vaccines for pertussis.
The older vaccine was a whole cell vaccine. That means it was created using the entire bacterium of the Bordetella pertussis germ.
It contained about 2,000 to 3,000 components that causes the immune system to prepare for a pertussis infection. However, it also could cause very high fevers that sometimes led to seizures, though with no long-term consequences.
The new vaccine is "acellular" and replaced the old one on the childhood schedule in 1997. It is made from protein pieces of the bacterium only.
The new vaccine contains only two to five components to stimulate the immune system, but it does not share the same serious side effects.
The researchers compared the medical records of children in the Kaiser Permanente Northern California medical system during the two-year pertussis outbreak in California in 2010 and 2011.
They specifically looked at children aged 10 to 17 who had been born between 1994 and 1999, in the middle of the transition from the old vaccine to the new vaccine.
All the children in the study had gotten all five shots of the pertussis vaccine by age 7, but some had gotten all the old vaccine while others got all the new vaccine or a mixture.
The researchers compared 138 children who had tested positive for pertussis during the outbreak to 54,339 children in the same medical system and age group who did not get pertussis. They also looked at 899 children who had been tested for pertussis but tested negative.
The researchers found that children who had received four shots of the new vaccine were almost six times more likely to get pertussis than those who had four shots of the old vaccine.
Those who had a mixture of the old and new vaccines during their first four shots were almost four times more likely to get pertussis than those whose four shots were all the old vaccine.
When the researchers looked specifically at the children who had gotten a mixture of the old and new vaccines, they calculated that each additional shot of the new vaccine gotten instead of the old one increased the child's risk of pertussis by 40 percent.
"A lot of studies are coming out showing the whole cell and acellular vaccines stimulate slightly different parts of the immune system," Dr. Klein told dailyRx.
"It may be that there is some fundamental difference that the whole cell stimulates in the immune system that has an effect years later that the acellular vaccine doesn't produce," she said.
However, she emphasized that the current vaccine does still work even though the immunity does not last as long.
Therefore, parents should follow the CDC schedule in vaccinating their children, especially being sure to get the additional recommended booster shots, she said.
"You now have a population of kids who have only received the acellular vaccine, so they'll be most benefited by getting booster," Dr. Klein said.
Thomas Seman, MD, a pediatrician at North Shore Pediatrics in Danvers, Mass. and a dailyRx expert, echoed the importance of staying up to date with booster shots for pertussis.
"The research demonstrates what we have been seeing in the real world. Pertussis is on the rise," Dr. Seman said.
"Maintaining immunization and proper reporting and testing for pertussis in children meeting symptom criteria is essential," he said.
Dr. Seman also explained a bit more about the background of the whole cell pertussis vaccine.
"The whole cell vaccine was known to be a very effective vaccine. However, some of the side effects seen in a percentage of children were not considered to be acceptable," he said.
"Some of these included seizures in approximately 8 percent of children, high fevers and significant swelling of the injection site causing severe pain," Dr. Seman said.
Although the new vaccine may not offer the same protection as the old one, Dr. Seman said every bit of extra protection helps.
"Any immunization and protection against this sometimes fatal disease is worth getting," Dr. Seman said. "Please keep vaccinating your child. You could save his/her life or that of another child."
The study was published May 20 in the journal Pediatrics. The research was funded by Kaiser Permanente. Two authors have received support from GlaxoSmithKline, Sanofi-Pasteur, Pfizer, Merck & Co, Novartis and MedImmune. The other authors declared no disclosures.
The pertussis vaccines studied in this research were manufactured by GlaxoSmithKline, Wyeth (now Pfizer), Sanofi-Pasteur, Merck & Co. and other pharmaceutical companies.