A booster vaccine aimed at protecting teens against whooping cough may wear off over time, a new study suggests.
In the study, researchers looked at about 1,200 cases of whooping cough (also called pertussis) that occurred among a population of about 280,000 teens in California between January 2006 and March 2015. Despite high vaccination rates against the disease among teens, there were two major outbreaks in this group in California, in 2010 and 2014.
The researchers found that, during the first year after a teen received the vaccination, the booster vaccine, called Tdap, had moderate effectiveness for protecting against the disease. It prevented 69 percent of cases of whooping cough in teens who were exposed to the bacteria that cause the disease.
However, that effectiveness dropped to less than 9 percent by four years after vaccination.
"The results in this study raise serious questions regarding the benefits of routinely administering a single dose of Tdap to every adolescent at age 11 or 12," lead study author Dr. Nicola Klein, co-director of Kaiser Permanente's Vaccine Study Center, said in a statement. "Because Tdap provides reasonable short-term protection, Tdap may contain pertussis more effectively if it is administered to adolescents in anticipation of a local outbreak rather than on a routine basis."
During the 1990s, the United States switched from whole-cell pertussis (DTwP) vaccine to the acellular pertussis (DTaP) vaccine, because there were concerns about the side effects of the whole-cell vaccine. Although the vaccine was very effective in preventing pertussis, it was linked with very high fevers, Klein said.
Currently, the DTaP vaccine is given during childhood in five doses, administered at ages 2 months, 4 months, 6 months, 12 to 18 months, and 4 to 6 years. However, despite high levels of vaccination, the United States and other developed countries have experienced an increase in whopping cough cases since the switch to DTaP, the researchers said. [5 Dangerous Vaccine Myths]
In 2006, officials began recommending that a booster shot with the acellular pertussis Tdap vaccine be given to kids at age 11 or 12.
In the new study, the researchers looked at the effectiveness of this booster during the two major outbreaks in California, in 2010 and 2014. Specifically, researchers looked at teens who had only ever received the newer acellular vaccine as kids, and not the older whole-cell vaccine.
Results showed that children who were 10 or 11 years old were the most likely to get sick with pertussis in each of the outbreaks. In other words, the kids were most likely to get sick just before they were scheduled to get their booster shots.
The researchers found that the effectiveness of Tdap vaccine decreased steadily with each year after vaccination. It prevented whooping cough 69 percent of the time during the first year, decreasing to 57 percent of the time during the second year and 25 percent during the third year. These numbers translate to a 35 percent decline in protection against the disease per year, the researchers said.
These results show that routine vaccination of adolescents at age 11 or 12 "provides moderate protection during the one year after vaccination," but then this protection decreases, Klein said.
As researchers work on developing new vaccines that could provide long-lasting protection against whooping cough, alternative strategies for Tdap immunization in teens should be considered, the researchers said.
The new study was published today (Feb. 5) in the journal Pediatrics.
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