Source: Seattle Times
By: Ostrom, Carol M.
Federal health officials have been investigating the whooping cough outbreak in Washington State, trying to determine why rates of the disease there this year are 10 times higher than in 2011. The state has the third-highest rate of whooping cough cases in the country, with 4,190 cases so far this year. Investigators with the Centers for Disease Control and Prevention (CDC) are looking at the immunization records of patients ages 11 to 18, the age group hit hardest by the disease. Seventy-seven percent of 13- to 19-year-olds diagnosed with whooping cough in the state had received their last recommended vaccination. They were also part of the first generation of teenagers to receive only the new formulation of the vaccine. In the late 1990s, pertussis vaccines switched from the whole-cell (DTP or DTwP) to the more highly purified acellular vaccines (DTaP and Tdap), which cause fewer side effects such as fever or seizures. However, the major spikes in pertussis cases were in younger teens who never received the whole-cell vaccine. One concern is that the new vaccine may not create a strong enough, or lasting enough, immune response. But pertussis is also a cyclical disease that will show high levels in one area one year but decline in others. A 2010 outbreak in California garnered the attention of researchers from the Kaiser Permanente Vaccine Study Center, who published a study showing that protection against pertussis waned during the five years after the last dose of the newer DTaP. After the data from Washington State is analyzed, the CDC’s Advisory Committee on Immunization Practices will recommend the next steps.