With the disease’s resurgence in recent years and an only somewhat effective vaccine, public health officials are pushing preventive measures meant to keep pertussis, more commonly known as whooping cough, at bay. That includes urging adolescents, pregnant women, adults, and those in contact with newborns, such as grandparents and caregivers, to get a booster shot.
Pertussis is characterized by fits of coughing, followed by a “whoop” sound from the attempt to inhale. A booster shot is an additional dose of the vaccine that “boosts” the immune system response as immunity to the disease wanes over time.
Massachusetts health officials said some people have been slow to follow the recommendations, but have encouragingly seen more people across all age groups receive the shots this year. Ninety percent of adolescents received the shot this year — a significant increase from 2005, when it was first licensed for middle-school age children — but it’s difficult to make sure that children who do not visit a pediatrician every year get the shot, said Dr. Lawrence Madoff, director of the Division of Epidemiology and Immunization at the Massachusetts Department of Public Health.
And few adults get the booster vaccine — only 36 percent in the state have ever received it. Experts say adults may not be aware they need it.
“The public at large and even physicians in general are inappropriately secure that early immunization has taken care of the problem and this is a disease of the past,” said Dr. Jeffrey Gelfand, an infectious disease physician at Massachusetts General Hospital and professor at Harvard Medical School. “The public still needs additional education. The public needs to be aware that we’re more susceptible than perhaps even 10 years ago.”
Cases of whooping cough in the United States were sparse for decades after a combined diptheria, tetanus, and pertussis vaccine was introduced in the 1940s. The shot was a whole-cell vaccine, meaning it used an entire inactivated Bordetella pertussis bacteria, the organism that causes the infection, so the patient could mount a robust immune response.
But after patients continually reported adverse side effects, such as swelling in the arm, fever, and even rare neurological problems, the vaccine was redesigned in the 1990s to only use fragments of the bacteria.
It used to be enough for infants and young children to get their school-mandated five doses of the old vaccine, which was expected to protect them for the rest of their lives. But the new vaccine, known as DTaP (the adult version is Tdap), while safer, is less effective. Massachusetts experienced a pertussis outbreak in 2012, with 653 cases and at least one death, and the country saw nearly 50,000 cases that year, the most since 1955. The rates have since decreased, with 346 cases in the state in 2013 and about 50 so far this year, according to DPH.
Immunity to pertussis wanes over time for those who receive the new vaccine. The DTaP shot is about 98 percent effective in its first year, but declines to about 70 percent effectiveness after five years, said Dr. Thomas A. Clark, director of the CDC’s Meningitis and Vaccine Preventable Diseases Branch.
“People think of a vaccine as: you get it and you’re sort of protected, or you don’t get it and you’re not protected,” Clark said. “It’s more a matter of degree. A vaccine can be 95 percent effective, but you can still be susceptible.”
A study from the American Academy of Pediatrics last year found that teenagers who received the new vaccine had a six times higher risk of contracting whooping cough than those who received the whole-cell vaccine. More than 85 percent of reported pertussis cases are in people who are vaccinated, Clark said.
Researchers are at least 10 years away from developing a new — and, they hope, more effective — vaccine, Clark said, so for the time being, there will be more cases. While some states that experienced outbreaks have since mitigated the spread of pertussis, including Massachusetts, health officials continue to see cycles of outbreaks. California declared a pertussis epidemic last month.
As more parents are choosing not to vaccinate their children, the lower number of immunized individuals, coupled with the vaccine’s waning immunity, has expedited transmission of pertussis and other diseases.
The Boston Globe