In the two weeks since California health officials declared a whooping cough epidemic, the state has added 1,100 more cases, officials with the California Department of Public Health said Friday.
That brings the total number of cases to 4,558. A third infant died of the disease recently. The baby, from Sacramento County, had started showing symptoms at just 3 weeks of age. The baby was hospitalized for more than a year and then passed away.
Infants are at particular risk because they cannot be vaccinated until they are several weeks old. Generally, the recommendation is that babies receive the first dose of vaccine at 8 weeks, but in light of the epidemic, state health officials say babies can be vaccinated at 6 weeks.
In addition, state epidemiologist Dr. Gil Chavez urged all pregnant women to be vaccinated against whooping cough, also called pertussis, in their third trimester of pregnancy. A mother's antibodies can transfer some immunity to the baby.
"Vaccination of pregnant women is the most important thing that can be done to protect infants until they are old enough to be vaccinated," Chavez said.
Women should receive a pertussis vaccine with every pregnancy, Chavez added. So even if a woman bore a child in the last few years, she needs to be revaccinated in the third trimester of a new pregnancy to help give each baby immunity from whooping cough.
Of the 4,558 cases, 142 have been hospitalized and more than 80 percent of those hospitalized are infants less than 4 months old.
While a great deal of attention has been paid to those who choose not to vaccinate their children, Chavez said the most important drivers of this year's epidemic are more likely the cyclical nature of whooping cough as an illness and the fact that the vaccine against whooping cough wanes over time. It does not confer lifetime immunity, and boosters are needed.
Chavez said the Centers for Disease Control and Prevention's Advisory Committee on Immunization is reviewing whether boosters of this newer whooping cough vaccine, introduced in the late 1990s because it reduces side effects, might need more frequent boosters. "We just have to wait and see if and when they make a different recommendation," Chavez said.
The three counties in the state with the highest rates of whooping cough are Marin, Napa and Sonoma. Marin has the highest vaccine-refusal rate in the Bay Area and one of the highest in the state. California last had a whooping cough epidemic in 2010. In later research, scientists determined that vaccine refusals helped to fuel that epidemic.
State health officials said they don't yet know if this year's epidemic will be worse than in 2010. In the meantime, officials say people should make sure vaccines for themselves and especially their children are up to date. The Centers for Disease Control and Prevention has an easy-to-use "adult vaccine finder" available to anyone. County health departments often provide vaccinations as well.