California Promotes Adult Vaccination to Combat Pertussis Epidemic

July 09, 2010

July 9, 2010 — The pertussis epidemic in California is taking its heaviest toll among infants, so state health authorities are trying to boost immunization in a population group thought to pass along the disease — adults.

The California Department of Public Health (CDPH) is shipping free pertussis vaccine to all birthing hospitals in the state, as well as county and municipal health departments, said CDPH spokesperson Mike Sicilia. The department is encouraging not only new mothers and fathers to get immunized but also other family members, healthcare workers, child care workers, and anyone else who might have contact with infants.

"We believe infants get this disease mainly from adults," Sicilia told Medscape Medical News.

The CDPH projects that California is on track to suffer its worst pertussis outbreak in 50 years. The state declared a pertussis epidemic on June 17. Through the first 6 months of the year it counted 1337 cases compared with 258 for the same period in 2009.

The incidence rate for children younger than 1 year was 38.5 per 100,000 — the highest rate among any age group. Of these children, 89% were younger than 6 months, which is too young to be fully immunized.

So far, the epidemic has claimed 5 lives — all Latino infants younger than 3 months who had not received any pertussis vaccine, according to the CDPH and the US Centers for Disease Control and Prevention (CDC). Pertussis rates for infants are higher for Hispanics than other ethnic groups in California.

As always, public health authorities stress vaccination as best way to protect against the disease. The CDC recommends that children receive the diphtheria, tetanus, and pertussis (DTaP) vaccine at ages 2 months, 4 months, 6 months, and 15 to 18 months, with a booster shot at age 4 to 6 years when they enter school. Infants need the first 3 shots in the series to achieve maximum protection, according to the CDC. Children aged 11 or 12 years should receive a dose of Tdap, the booster shot for adolescents and adults. Adults who did not receive Tdap as a preteenager or teenager also should get a dose.

California does an above-average job of immunizing young children. In 2008, the coverage rate for 3 or more doses of DTaP among children 19 to 35 months of age was an estimated 97.8% for California compared with 96.2% for the nation, according to a survey by the CDC. The immunization rate for California Latinos was even higher, at 98.1%.

Similar to the rest of the country, however, California falters when it comes to vaccinating children aged 11 and 12 years. In 2008, the percentage of children aged 13 to 17 years who had received at least 1 dose of Tdap since age 10 years was 44% in California and 41% nationwide. A bill is pending in the California state legislature, however, that would allow the state to require middle-school children to be vaccinated against pertussis.

The immunization rate among adults nationwide is even worse, at 6% (the corresponding rate in California is not available). It is the lack of vaccine coverage among adults that California is attacking in the midst of its pertussis epidemic.

"What We're Seeing Here Is Not a Surprise"

Gilberto Chavez, MD, chief of the Center for Infectious Diseases in the CDPH, attributes the pertussis epidemic to the cyclical nature of the disease. Cases peak every 3 to 5 years as vaccine-induced immunity in the general population wears off, Dr. Chavez said. The last outbreak in California, as well as the rest of the United States, was in 2005.

"We knew we were due for [another] one," Dr. Chavez told Medscape Medical News. "What we're seeing here is not a surprise."

His department is duly investigating the possibility that California is facing a superbug strain of pertussis. "So far we have found no evidence of a new strain that can't be protected against by a vaccine or treated with an antibiotic," he said.

Socioeconomic factors probably account for the death toll being confined so far to Latino infants, Dr. Chavez said, noting that infants younger than 3 months would not be fully immunized even if they had gotten their first dose of vaccine.

"Poor outcomes could be due to poor access to care," said Dr. Chavez, pointing to higher rates of poverty and lower rates of health insurance coverage among Latinos. "And it may be they don't have enough information on the way the disease presents itself to seek care on a timely basis."

Nationwide, Pertussis Cases Are Down 14%

Although whooping cough grabs headlines in California, it has not reached epidemic proportions elsewhere, according to Stacey Martin, MSc, a pertussis expert and epidemiologist at the CDC.

To be sure, the CDC has seen increased pertussis activity in states such as Michigan, South Carolina, and Arizona during the first half of 2010. However, Pennsylvania, Missouri, New Jersey, and other states have reported a substantial decrease in cases.

Through July 3, pertussis cases nationwide have fallen off by 14% compared with 2009, according to the CDC.


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