Children fully inoculated against whooping cough become more susceptible to the disease as the vaccination wanes over time, contributing to outbreaks in the U.S., a study found.
Each year after receiving the fifth dose of the vaccine, children had a 42 percent increased risk of acquiring whooping cough, also known as pertussis, according to research in the New England Journal of Medicine. The vaccine, known as DTaP, which also inoculates against diphtheria and tetanus, is sold in the U.S. by GlaxoSmithKline Plc (GSK) and Sanofi.
About 25,000 cases of whooping cough have been reported in the U.S. this year through Aug. 24. The totals have almost reached the 27,550 cases for all of 2010, which included an epidemic in California and was the most since 1959, according to the U.S. Centers for Disease Control and Prevention. Strengthening the current vaccine or developing more effective shots are needed to help stop the spread of the bacterial infection, said Nicola Klein, the lead study author.
“A large part of the reason the epidemics have been occurring here and in other states around the country has to do with this waning immunity in this school-aged population,” Klein, a research scientist and co-director of the Vaccine Study Center at Kaiser Permanente, an Oakland, California-based health plan, said in a Sept. 10 telephone interview.
“The long-term solution is we need new vaccines that have long-lasting immunity or to reformat the current vaccines to provide long-lasting immunity. The current vaccines are safe and effective and some protection is better than no protection. They just don’t perhaps last as long as we would probably like.”
Pertussis is a highly contagious disease that causes violent coughing, making it difficult to breathe. It may lead to permanent disability or death, particularly in young children, according to the National Institutes of Health. Patients struggling to take a breath make a “whooping” sound that gives the disease its name.
The study released yesterday is the first to include children who have been fully inoculated with the current pertussis vaccines, which are given in five doses starting at 2 months through 4 to 6 years old. Klein said it is challenging to find a cure for pertussis because getting it once doesn’t stop a person from becoming infected again.
Tom Clark, a medical epidemiologist at the Atlanta-based CDC, said it may take 10 years before a change is made to the current vaccines or new vaccines are developed to fight pertussis.
“The news that protection from the vaccines wears off should not make people doubt the vaccine,” Clark said in a Sept. 10 telephone interview. “The vaccine is the best protection we have.”
Researchers have known the effectiveness of the vaccine wanes over time, which is why the CDC recommends a booster shot for adolescents and adults, Michael Szumera, a spokesman for Paris-based Sanofi (SAN), said in a Sept. 10 e-mail. The company is studying several new and improved pertussis vaccines in clinical trials, he said.
GlaxoSmithKline is working with the CDC and other public- health authorities to better understand what is causing the increased number of U.S. pertussis cases, Rob Perry, a spokesman for the London-based drugmaker, said in a Sept. 11 e-mail. It’s premature to develop new pertussis vaccines before fully understanding what is causing the current outbreaks, he said.
Researchers in the study compared 277 children ages 4 to 12 who were positive for whooping cough with 3,318 children who were negative and 6,086 controls. They looked at pertussis in children from 2006 to 2011 in California and measured the time since their fifth vaccination.
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