The effectiveness of a vaccine that helps protect teenagers against whooping cough, also known as pertussis, may decrease over time, according to a new study.
In the study – published Friday (Feb. 5) in the journal Pediatrics – the researchers analysed approximately 1,200 cases of whooping cough that occurred from January 2006 to March 2015, among 280,000 adolescents in California. Two major outbreaks took place in 2010 and 2014, despite high vaccination rates, the researchers found.
The booster vaccine, called Tdap, was moderately effective during the first year after vaccination. Tdap protected teenagers who were exposed to the bacteria that cause whooping cough in 69 percent of the cases. Four years after the vaccination took place, the effectiveness decreased to less than nine percent, according o the researchers.
Dr. Nicola Klein, lead author of the study and co-director of Kaiser Permanente’s Vaccine Study Center, said that the study results raise some questions regarding the benefits of administering a single dose of Tdap in teenagers ages eleven to twelve years. Tdap provides short-term protection, so it may be better to administer before a local breakout, and not on a routine basis, Dr. Klein explained.
In the 1990s, the United States replaced the whole-cell pertussis (DTwP) vaccine with the acellular pertussis (DTaP) vaccine. According to Klein, people were concerned about the side effects of DTwP – such as very high fevers.
The acellular pertussis (DTaP) vaccine is currently administered at ages two, four, six, twelve and eighteen months old, and when the child is four to six years old. Ever since the switch to DTaP, some countries, including the United States, have seen an increase in whopping cough cases, even though the levels of vaccination are high.
For the new study, the researchers examined the effectiveness of the acellular pertussis (DTaP) vaccine during the major cough outbreaks that took place in 2010 and 2014 in California. They focused on the adolescents who received the DTaP vaccine as kids, and not the whole-cell pertussis vaccine.
The findings show that in each of the outbreaks, children ages ten to eleven were the most likely to get sick with whopping cough. Moreover, the researchers also found that the Tdap vaccine became less effective with each year after vaccination.
Every year, the vaccine’s protection against the disease, dropped by about 35 percent. During the first year, it prevented whopping cough about 69 percent of the time, but the prevention rate decreased to 57 percent during the second year, and then to 25 percent during the third year.
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