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Waning and Less Effective Acellular Whooping Cough Vaccines Likely Contributed to the 2010 California Whooping Cough Outbreak

OAKLAND, Calif. – Waning and less effective acellular whooping cough vaccines likely contributed to the 2010 California whooping cough outbreak, according to researchers from the Kaiser Permanente Vaccine Study Center.

The Research is being presented this week at the 49th Annual Meeting of the Infectious Diseases Society of America, held in Boston MA.

Researchers found that DTaP vaccine (given to children younger than 7 to develop immunity for diphtheria, tetanus, and whooping cough) wanes about 40 percent each year.   This means that if the vaccine is 90 percent effective after given, after the 5th dose (given before children enter kindergarten) it is less than 50 percent effective, according to the researchers.

In 2010 California experienced the highest rate of whooping cough (pertussis) in over 50 years.  This increase comes after decades of gradually increasing rates since the the US change over to acellular vaccines  in the early 1990s, said the researchers.

Kaiser Permanente Vaccine Study Center co-directors Roger Baxter, MD, and Nicola Klein, MD, PhD, have previously presented on pertussis vaccine effectiveness and waning —  Baxter at the National Foundation of Infectious Diseases conference held in the Spring of 2011 and Klein at the European Society for Pediatric Infectious Diseases in The Hague, The Netherlands held in June 2011.

At this week’s 49th Annual Meeting of the Infectious Diseases Society of America, Kaiser Permanente researchers are also reporting on the effectiveness of the booster vaccination given to older children and adults.  The booster vaccination given to adolescents and adults (Tdap) was about 55 percent effective, according to Vaccine Study Center do-director, Roger Baxter who led this portion of the research. Researchers did not see evidence of waning, but explain that most people in their analysis had received the vaccine within three years.

“All the findings point to the fact that vaccine guidelines and pertussis control measures may need to be reconsidered,” said Baxter and Klein, explaining that because of the safety concerns regarding whole cell pertussis vaccines, it is unlikely that the parents or medical providers in the United States would return to using them. “These results point to the need for new and improved pertussis vaccines,” they said.

The first pertussis vaccine was developed in the 1930s and was in widespread use by the mid-1940s, when pertussis vaccine was combined with diphtheria and tetanus toxoids to make the combination DTP vaccine.

A series of 4 doses of whole-cell DTP vaccine was 70–90 percent effective in preventing serious pertussis disease, said the researchers, explaining that up to half of the children who received the vaccine developed local reactions such as redness, swelling, and pain at the injection site.

In 1991, concerns about safety led to the development of more purified (acellular) pertussis vaccines that are associated with fewer side effects. These acellular pertussis vaccines have replaced the whole cell DTP vaccines in the United States, they explained.

In 2005, two new vaccine products were licensed for use in adolescents and adults that combine the tetanus and diphtheria toxoids with acellular pertussis (Tdap) vaccine. These vaccines are the first acellular pertussis-containing vaccines that make it possible to vaccinate adolescents and adults against pertussis, said the researchers.

For the findings being presented this week, researchers examined the relationship of vaccination with the likelihood of a positive pertussis test in the Kaiser Permanente Northern California population which includes 3.3 million members in in integrated care system with electronic medical records and a central laboratory.

Additional investigators on the research include: Joan Bartlett, Kaiser Permanente Division of Research; Bruce Fireman, MA, Kaiser Permanente Division of Research; and Ali Rowhani-Rahbar, MD, PhD, Kaiser Permanente Vaccine Study Center.

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