The booster vaccination given to preteens to prevent whooping cough provides moderate protection in the first year, but decreases over time, suggests a new study. The research, published online Feb. 5 in Pediatrics and scheduled to appear in the journal’s March print issue, found that four years post-vaccination effectiveness was reduced to 9 percent.
According to study researchers from Kaiser Permanente’s Vaccine Study Center, waning immunity may have been a major contributor to the California epidemic breakouts of the disease in 2010 and 2014. Despite routine vaccination coverage in 90 percent of adolescents, this age group had the highest incidence of whooping cough in 2014.
Cases of whooping cough – also known as pertussis – have been on the rise for years. The Centers for Disease Control and Prevention (CDC) reported that in 2012, there were more than 48,000 incidences of the disease nationwide – the highest number since 1955. The agency also said that older children and teens accounted for a growing portion of the cases.
Health experts attribute the increase to a change in the vaccine in the 1990s, when U.S. health officials switched from the whole cell pertussis (DTwP) to acellular pertussis (DTaP) vaccines for all five doses at ages 2, 4, 6, 12 to 18 months and 4 to 6 years. In 2006, a booster Tdap vaccine was recommended for all kids ages 11 to 12.
“The issue is the old vaccine against whooping cough had a difficult safety profile,” Paul Offit, MD, director of the Vaccine Educational Center and a professor of infectious diseases at Children’s Hospital of Philadelphia, told HealthDay. It could cause high fevers and seizures in young children, and there were concerns about possible, albeit rare, neurological effects, explained Offit, who was not involved in the study.
Those concerns led to the development of DTaP, which has far fewer antigens than the old vaccine. Antigens are proteins that trigger an immune system response. Fewer antigens mean the DTaP vaccine is much less likely to cause side effects. The trade-off, however, appears to be a shorter-lived immunity.
To explore Tdap effectiveness among teens during the 2010 and 2014 outbreaks, researchers led by Nicola Klein, MD, PhD, co-director of Kaiser Permanente’s Vaccine Study Center, looked at booster coverage among kids aged 10 and up who had been vaccinated with DTaP vaccines. They found that more than 96 percent had been vaccinated with the Tdap by their 14th birthday.
Findings showed that Tdap provided moderate protection against the disease in the first year following vaccination, preventing 69 percent of whooping cough cases in teens. However, the shot’s effectiveness dropped to 57 percent during the second year and 25 percent during the third year. By year four, the vaccine’s effectiveness had plummeted to 9 percent.
“This study demonstrates that despite high rates of Tdap vaccination, the growing number of adolescents who have received only the newer acellular pertussis vaccines [when they were young] continue to be at higher risk of contracting whooping cough and sustaining epidemics,” Klein said in a news release. “I think waning immunity – primarily from the DTaP but also Tdap – are the main drivers behind these outbreaks.”
Both Klein and Offit, see the need for the development of new vaccines that will provide longer-lasting protection against whooping cough. In the meantime, they noted consideration should be given to alternate Tdap immunization strategies for adolescents, suggesting it might be effective to give it in “anticipation” of an outbreak.
So what should parents do until there is a new vaccine?
Infectious disease specialist William Schaffner, MD, a professor at the Vanderbilt University School of Medicine, told USA TODAY that although the current vaccine is imperfect, it is still the best way to protect children from the disease. He advised parents to continue vaccinating their kids as scheduled.
“If we routinely vaccinate all middle-schoolers, they will at least have short-term protection,” said Schaffner, who was not involved in the study. “Let’s not throw the baby out with the bath water.”
The health experts also urged pregnant women to get a Tdap shot with each pregnancy. Not only does it protect the moms, it also provides protection to the babies for the first few months of life. Newborns are most vulnerable to and most likely to die from whooping cough.