As San Luis Obispo County reported this week that it has one of the highest numbers of whooping cough cases in the state, local health officials said it’s likely due to waning immunizations among children and young adults.
As of Wednesday, the county reported 258 cases, compared to Marin County, with 232 cases. The two counties had the highest numbers of whooping cough cases in a statewide survey earlier this month.
“Typically, outbreaks have to do with high numbers of susceptible populations,” Ann McDowell, an epidemiologist with County Public Health, said Friday. “There appears to be some waning immunity (locally).”
Waning immunity is the term often used when vaccines begin to lose their effect, making a person susceptible to disease or infection absent another dose of vaccine. Susceptible populations also include those that haven’t been vaccinated.
McDowell said cycles of outbreaks occur every three to five years and that in the past two years only 19 cases were reported in the county.
Of the current local cases, about half — 122 — are children between ages 6 and 15.
Some parents choose not to have their children immunized, which can leave them susceptible to infections, McDowell said. Children should receive five doses during childhood.
Others don’t realize children should receive a booster shot around age 10 or 11 — leaving those who don’t get the booster vulnerable around that age.
Whooping cough can be transmitted through the air.
McDowell stressed that “anyone around a baby should get shots because infants have the highest risk and can die.”
San Luis Obispo County had the second-highest number of whooping cough cases in the state as of July 13 with 193. That number rose to 258 as of Wednesday.
Marin County, with 232 cases, was the highest in the state as of July 13 in the most recent statewide reporting.
Marin County Public Health Officer Fred Schwartz said waning immunity appears to be a problem there as well.
“We see our greatest numbers among children and teens,” Schwartz said. “It’s very important for kids to be brought up to date (with shots).”
Tribune staff writer AnnMarie Cornejo contributed to this report.