Children stricken with whooping cough or pertussis were less likely than healthy children to have gotten all five doses of the vaccine, known as the DTaP (diphtheria, tetanus, and acellular pertussis vaccine), according to a new study.
As time went on from the last vaccine dose, protection waned for children, even if they got all five recommended doses, the new research finds. Other researchers have also found waning immunity.
For the new study, the researchers looked at the records of children in California, where in 2010 the state had its largest whooping cough epidemic in more than 60 years. In the 2010 California epidemic, more than 9,000 pertussis cases were reported and 10 babies died.
The disease starts as a common cold, but after one or two weeks, the severe coughing can begin. Infants cannot have the cough but have dangerous breathing pauses instead.
The researchers compared 682 children, ages 4 to 10, who had whooping cough with 2,016 children in the same age group who did not.
"The good news from our study is, the vaccine is still protective," says Stacey Martin, M.Sc., a researcher with the Centers for Disease Control and Prevention. The study is published Nov. 28 in the Journal of the American Medical Association.
"Unvaccinated children had eight times the risk overall of pertussis as vaccinated children," Martin tells TakePart. "It's important parents remember this is the best tool."
However, the protection did drop as time went on, she tells TakePart. "By the time they are around age 10, their protection has waned substantially, to roughly 71 percent," she says.
Those who got whooping cough were less likely to have gotten their fifth dose within the past 12 months, but to have received it more than a year ago, she found.
The CDC recommends the five-dose series at two, four and six months of age, with a fourth shot given at 15 through 18 months of age. The fifth is given about ages four to six.. A booster dose is recommended at 11 or 12 years.
Because the first vaccine dose is not given until age two months, very young babies are especially vulnerable.
New research, including previous studies, has raised concern about the current U.S. whooping cough vaccine schedule, the authors say. It may prompt consideration of alternative schedules.
The researchers have given the data from the new study to the CDC's Advisory Committee on Immunization Practices, Martin says. "At this time, there are no plans to change the current schedule," she says.
The CDC's advisory committee is promoting vaccination in pregnant women, however, she says. "The ACIP has just voted that every pregnant woman, every pregnancy, get vaccinated against pertussis," Martin says. The recommendation is provisional until it is published in the CDC's Morbidity & Mortality Weekly Report. That is expected by year's end, she says.
Ultimately, Martin says, improved protection from whooping cough may require a new vaccine that gives longer duration of protection.
"There is research being done in that area," she says. However, that isn't expected to become reality soon. "We're probably a good decade away from a new vaccine for pertussis," she says. "Right now we need to use the vaccine we currently have, the best we can. And the current vaccination schedule is the best way to do that."
"We need new vaccines," agrees James Cherry, M.D., professor of pediatrics at the David Geffen School of Medicine at the University of California Los Angeles. He is an expert on pertussis vaccines. He has consulted for Sanofi Pasteur, which markets a whooping cough vaccine.
"In the interim, we are still much better off than we were in the pre-vaccine era," he tells TakePart.
In a commentary published earlier this year in the New England Journal of Medicine, Cherry put the problem in perspective. He says that today's incidence of pertussis is about ''one twenty-third of what is was during an epidemic year in the 1930s."
That was before the diphtheria, tetanus and whole-cell pertussis vaccine, different from today's, was introduced in the late 1940s.
Meanwhile, as of mid-November, 36,000 cases of whooping cough and 16 deaths from pertussis have been reported to the CDC. That number already surpasses the number of cases in 2010, according to the CDC.