A booster vaccine given to pre-teens to protect them from whooping cough only works for a short period of time, a new study suggests. The waning of immunity is seen as a big factor in recent outbreaks that occurred in California, where two major outbreaks occurred in 2010 and 2014 despite having high vaccination rates.
For the study, researchers looked at the data of teens who received DTaP vaccination. More than 96 percent of these subjects also had the booster shot Tdap by their 14th birthday.
The DTaP vaccine is given during childhood but regardless of high vaccination rates in the U.S., cases of whooping cough remained high since DTaP replaced the DTwP vaccine, which was linked with very high fevers. In 2006, the booster Tdap vaccine was recommended for kids between 11 and 12 years old.
To assess the effectiveness of the booster, the researchers looked at whooping cough cases during the two major outbreaks in California and found that Tdap provided "moderate" protection against the disease for about a year preventing 69 percent of whooping cough cases in teens who were exposed to the bacteria that caused the disease.
The immunity though waned quickly that those who were given shot had little protection after two or three years. The effectivity of the shot decreased to 57 percent during the second year and 25 percent during the third year. By the fourth year after vaccination, the effectiveness of the vaccine dropped to less than 9 percent.
"The strategy of routinely vaccinating adolescents to prevent future disease did not prevent the 2014 epidemic, arguably because the protection afforded by a dose of Tdap was too short-lived," said study researcher Nicola Klein, co-director of Kaiser's Vaccine Study Center, in California.
Klein said that the findings of the study show that current vaccines are not enough to prevent epidemics. She even pointed out that waning protection from DTaP and Tdap plays a crucial part in the occurrence of pertussis outbreaks.
"I think waning immunity -- primarily from the DTaP but also Tdap -- are the main drivers of these outbreaks," Klein said.
The study was published in the journal Pediatrics on Feb. 5.
