The United States last year saw its highest number of whooping cough cases since 1959, according to the U.S. Centers for Disease Control and Prevention, a fact made more acute since recent research shows the effectiveness of the vaccine wanes over time.
A number of factors play into the rise in cases nationally, said Patti Bull, infection prevention coordinator at Hendrick Medical Center in Abilene, Texas.
"For various reasons, we're seeing a lot of people that are choosing to not immunize their children," she said. "We're also finding out as we grow older, the vaccine (effectiveness) seems to be waning somewhat."
Whooping cough, named for a distinctive sound made by some with the illness, attacks the respiratory system.
Adults who get the disease are not "as commonly diagnosed" with it, because their symptoms are less severe than in children, Bull said.
"So we become the 'pool,' if you will, continuing to pass it along," she said. "And with this new generation of more unvaccinated children, we're seeing more of a resurgence of the disease."
Also called pertussis, the illness can be deadly to infants, causing coughing fits, choking, pneumonia, brain damage and even death, according to preventpertussis.org, a site created by the Texas Department of State Health Services.
The illness responds well to antibiotics "if you recognize it early," said Zane Travis, medical authority with the Abilene-Taylor County Public Health District.
New research by the CDC has shown the current vaccine's effectiveness wanes after its fifth dose, commonly given when a child is age 4 to 6, and an adolescent booster, recommended around ages 11-12.
Newborns and infants are supposed to begin receiving pertussis vaccinations, along with protection against diphtheria and tetanus, at 2, 4 and 6 months, with a fourth dose at 15-18 months.
Health officials still recommend parents follow the CDC's vaccination schedule for their children, noting those who are vaccinated tend to have milder bouts with the disease.
And "adults who are exposed to a lot of young kids should probably receive a booster dose," Travis said, adding that patients with a cough with no obvious cause lasting more than two weeks should be tested for pertussis.
In 2012, 41,000 cases and 18 deaths from pertussis were reported nationwide. Most of the deaths occurred in infants.