Holbrook says California is seeing a whooping cough epidemic partly because the disease is cyclical, with cases spiking every three to five years.
Additionally, Holbrook says, the immunity from the current vaccine, introduced in the 1990s, fades more quickly than the previous version. The current vaccine has fewer side effects.
Holbrook says she also thinks clinicians in her county are doing a good job of recognizing and diagnosing cases. “I can’t prove that relative to the other counties, but I honestly feel that that’s contributing to our (higher) rate,” she said.
Marin County Public Health Officer Matthew Willis says not all communities will have the same incidence of pertussis because of different factors and vulnerabilities, both known and unknown. Of the known factors, Willis echoes Holbrook’s points — and adds one more: vaccination rates.
“In Marin, it’s likely that pertussis was able to establish more of a foothold because of lower vaccination rates,” Willis says. Marin’s rate of personal belief exemptions, which allow parents to opt out of vaccines for their children, is among the highest in the state, according to statewide data.
One thing is clear, he says: Vaccination is the most effective way to prevent pertussis. The vaccine does not provide lifetime immunity and boosters are needed.
Of those who should be vaccinated, babies and pregnant women are of particular importance, says Jennifer Henn, an epidemiologist with Napa County's Public Health Division. “Infants, especially infants under six months of age, are especially vulnerable to severe disease and even death if they become infected with the pertussis bacteria.”
Infants generally cannot get their first pertussis vaccine until they are eight weeks, but in light of the epidemic, state health officers said babies can be vaccinated as young as six weeks. Pregnant mothers should be vaccinated in the third trimester of every pregnancy in order for their children to receive antibodies in the womb. People who are around infants, such as other members of the household or caregivers, should also be vaccinated.