Growing outbreaks of whooping cough — including a California epidemic that has killed six babies — are worrying public health officials who fear that sporadic vaccination practices may be contributing to dangerous cases of the preventable disease.
More from TODAY.com
Handlers of retired Marine hero, bomb-sniffing dog give thanks
Cpl. Juan Rodriguez's actions saved the dog's life, but he said, "she saved mine multiple times so it was only right."
- Why are you thankful this Thanksgiving? Show us! #WhyImThankful
- Read father's letter to girl whose sky lantern landed in his driveway
- Add Martha Stewart's Thanksgiving favorites to your holiday dinner
- Make Giada DeLaurentiis's Thanksgiving favorites for your family
- Handlers of retired Marine hero, bomb-sniffing dog give thanks
"I'm saddened, but I can't truly say I'm surprised," said Dr. Saad B. Omer, an assistant professor with Emory University's Rollins School of Public Health and an national expert on immunization practices. "We know and we have known for a while that we have these gaps in protection at the local level."
Rising cases of the disease also known as pertussis have been reported in Idaho, Texas, South Carolina, Michigan and in California, where 1,500 children have been diagnosed in what's being called the worst outbreak in 50 years.
In some places, including Michigan and California, there are communities where parents have refused recommended vaccinations, often because they fear complications from the shots.
'Herd immunity' breached
When that happens, vaccine resisters breach what's known as "herd immunity," the necessary level of protection that keeps disease from spreading. That allows infection to infect vulnerable people, including those for whom a vaccine doesn't work or wears off, and babies too young to be immunized.
There's some evidence that being under-vaccinated or not vaccinated at all is contributing to a portion of the cases in the California outbreak and others, said Dr. Tom Clark, a medical epidemiologist with the federal Centers for Disease Control and Prevention. He declined to say what proportion of the ill children in California were not fully vaccinated.
In other cases, the illness is showing up in children ages 7 to 10, kids whose older vaccinations may be waning, but who have not yet received recommended doses for adolescents.
Vaccines for pertussis are given to children at 2, 4 and 6 months and then again at about age 11 or 12. Experts also recommend that adults who are around children under the age of 1 get vaccinated.
Pertussis is a bacterial infection that can cause uncontrollable coughing and respiratory distress. It's dubbed "whooping cough" because of the sound a victim makes trying to catch breath between bouts of coughing. Peak season is late summer and early fall, which may mean more outbreaks ahead.
Whooping cough outbreaks tend to run in three- to five- year cycles, said Chris Van Deusen of the Texas Department of State Health Services. There, outbreaks have been seen in pockets across the state with the biggest increase in Central Texas areas.
"There it's significantly higher than the usual rates but it's not a statewide problem," said Van Deusen said.
Counties report more cases
Some counties in Michigan are reporting more cases so far this year than in the past 10 years. South Carolina has 168 reported cases so far this year, higher than those reported during the same time period since 2006. In Idaho, 77 cases of whooping cough have been reported in in the first six months of the year, according to the Idaho Department of Health and Welfare. That's up from 45 cases reported in the same period last year.
Idaho state epidemiologist Dr. Christine Hahn says the department is encouraging families to get vaccinated against the illness. She says infants will be better protected against potentially fatal whooping cough if adults and adolescents in their families have up-to-date vaccinations or booster shots.
In 2009, a study showed that children who don't get whooping cough vaccine are 23 times more likely to get the disease than vaccinated kids. The study, published in Pediatrics, was of 751 children in Kaiser Permamente of Colorado's health plan.
But Barbara Loe Fisher, president and co-founder of the National Vaccine Information Center, which generally opposes vaccination, says that parents who choose not to immunize their kids can't be blamed for the growing outbreaks.
Pertussis can infect even vaccinated people, and the vaccines aren't always effective, she said. In addition, the pertussis bacteria may be becoming resistant to the vaccines, something the CDC is investigating, Clark said. She urged parents to consider their options carefully.
"It's always a balance to weigh the risk of the complications of pertussis, which can be serious for some children, and the risks, known and unknown, of the vaccines," Fisher said.
© 2013 msnbc.com