(dailyRx News) Vaccines may be one of medicine's greatest inventions, but they're not perfect. Some can lose effectiveness over time, like the DTaP that protects against whooping cough.
Whooping cough is a common name for pertussis. As these cases have been increasing in recent years, researchers are realizing the vaccine is wearing off sooner than expected.
A new study finds that the pertussis vaccine starts to fade in the five years after the final childhood booster.
The study, led by Nicole P. Klein, MD, PhD, from the Kaiser Permanente Vaccine Study Center, involved children who have received only the DTaP (diphtheria - tetanus - acellular pertussis) vaccine and its boosters since they were born.
Previously, a different vaccine called the DTP was given to children. It also covered diphtheria, tetanus and pertussis, but it used larger pieces of the pertussis virus.
It was discontinued in the 1990s because of a higher risk of seizures caused from high fevers. These seizures did not cause long-term damage or death, but they were frightening.
The DTaP was recommended by the U.S. Centers for Disease Control and Prevention in 1998 and includes five shots given to children starting at 2 months. The last booster is recommended between age 4 and 6.
No children who had received the DTP vaccine were included in this study, which compared three groups of children, aged 4 to 12, during the 2010 pertussis outbreak in California.
The study groups included 477 children who tested positive for pertussis, 3,318 children who tested negative for pertussis, and 6,086 children as controls for a comparison group.
They determined the risk of pertussis after receiving the fifth DTaP booster between 2006 and 2011.
They found that the pertussis part of the DTaP vaccine declined in effectiveness about 42 percent each year.
This means that each year after a child's fifth booster, the child's risk of contracting pertussis increased by 42 percent.
The amount of decrease in the vaccine's effectiveness depends on how effective the fifth booster shot was for the child.
For example, the researchers write, if the fifth DTaP booster had 95 percent effectiveness, that would have dropped to about 71 percent effectiveness five years later.
But an initial effectiveness of 90 percent translate to only 42 percent effectiveness five years later.
The authors note that past clinical trials of the DTaP "suggested that protection against pertussis was sustained 5 to 6 years after vaccination."
However, other studies have shown declines in effectiveness over time and the possibility of the vaccine not working at all eventually, which matched the findings in this study.
Because the 2010 outbreak had the highest number of cases among children aged 8 to 11 who had received all five DTaP shots, the researchers said it appears the decreasing effectiveness of the vaccine likely contributed to the continuation of the outbreak.
The authors therefore concluded that even though getting all five shots of the DTaP is important for children, more should be done to ensure they are effectively protected until they can get the TDaP shot. The TDaP is the adult pertussis vaccine.
"Our findings highlight the need to develop new pertussis-containing vaccines that will provide long-lasting immunity," they wrote.
The study was published September 12 in the New England Journal of Medicine. The research was funded by the Kaiser Permanente Vaccine Study Center.
Dr. Klein and another co-author have received grant support from pharmaceutical companies Sanofi Pasteur, GlaxoSmithKline, Novartis, Merck and Pfizer. No other authors reported competing interests.