Outbreak of whooping cough a new normal


Whooping cough is here to stay, according to Marin County Public Health Officer Matt Willis, and the best way to protect the most vulnerable is through the vaccination of pregnant women.

There were 249 cases of the illness—formally known as pertussis—in Marin County last year, and nearly 3,000 cases statewide. Although pertussis is technically a vaccine-preventable disease, the vaccine is only partially effective, protecting people heartily for two to three years. After that, the efficacy will wane, Dr. Willis said.

The new numbers are “likely to represent a new normal for us,” he said. High schools are particularly fertile ground for outbreaks; last spring, students at Sir Francis Drake High reported the highest number of infections—56—of any high school in the county. As vaccines are required before kindergarten and seventh grade, Dr. Willis suggested that upperclassmen are especially vulnerable because the efficacy of their vaccines has largely worn off.

“One of the key strategies in terms of actually preventing pertussis mortality is pre-natal vaccinations,” he said. Pertussis is most dangerous for infants under 10 months old, and babies cannot be vaccinated against pertussis for two months due to their vulnerable immune systems. But “when a mom is vaccinated in her third trimester, her body will make antibodies against pertussis and that child is born protected,” Dr. Willis explained.

The number of whooping cough cases has increased alongside what Dr. Willis called a “reassuring and dramatic increase” in the vaccination rate in the county over the past four years. In the 2012-2013 school year, only 78 percent of students were fully vaccinated; the rest took personal-belief exemptions. In 2016, California passed a bill that eliminated such exemptions, and in 2018 the vaccination rate across Marin was 95 percent.

But Dr. Willis stressed that much of the progress was made even before the law’s passage. “It’s a simplification to say that a policy solely changed vaccination rates,” he said. “It was a much more encouraging dynamic, where people were choosing to protect themselves and their community when the threats themselves were increasing.”

The county is also working to educate high schools to keep infected students out of school and make sure they are treated with antibiotics to prevent the disease from spreading. Ultimately, Dr. Willis said, all of the measures work together to form a “way of eliminating the overall community burden.”