Washington’s worst epidemic of whooping cough in 70 years appears to be winding down. The number of cases is a fraction of the peak last May.
A briefing Wednesday afternoon at the State Board of Health highlights the ongoing investigation into what happened.
A team of about 50 federal scientists spent the summer visiting doctors' offices, reviewing patient records, and compiling evidence.
Whooping cough outbreaks tend to come in waves, every four or five years. But, this time the disease spread much more widely than a typical outbreak, which also happened in California in 2010 and Wisconsin this year.
Health officials suspect one problem is that a newer version of the whooping cough vaccine, called the DTaP, is weaker than the older version. It uses an "acellular" bacteria, instead of the full-cell. The formulation was changed nationally in the 1990’s, to reduce side-effects for children, such as pain and swelling.
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But, it now appears to investigators that the new formulation wears off a lot faster, and makes the booster a bit less effective. That's why the hardest-hit age group was 10-13-year-olds, who hadn't yet got their booster, called the Tdap.
Washington Secretary of Health Mary Selecky urges adults and teens to get a one-time whooping cough booster shot, which has only been available for the last five years. If an infant is exposed, possibly by a sibling or parent or grandparent, the disease is severe, sometimes fatal.
"While the epidemic is in its last days, we aren't ready to declare its over," says Selecky, with about 20 new cases per week, compared to ten or fewer per week in a typical year -- and more than 200 per week last May.
As of Nov. 13th, Washington had a total of 4,501 confirmed cases of whooping cough this year. That's more than double any year since 1941, when the year-end total was 4,960, according to the Department of Health. The vaccine against whooping cough, or pertussis, was licensed in the U.S. in 1949, and became widespread as part of the "DTP" combination (Diptheria-Tetanus-Pertussis) in the early 1950s.
