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In a new large study on Kaiser Permanente, children who adhered to the pertussis vaccination schedule were much less likely to develop the disease than unvaccinated children. However, most pertussis cases involved fully immunized children. The risk that vaccinated children become sick increases with the time since vaccination, suggesting that the decrease in efficacy between doses has contributed significantly to recent outbreaks.
The study entitled "Effectiveness of acellular pertussis vaccine over time" was published on June 10 in the journal pediatrics.
Pertussis, known as whooping cough, is a highly contagious and potentially fatal respiratory infection caused by Bordetella pertussis. To help prevent it, the Centers for Disease Control and Prevention (CDC) recommends five doses of DTaP vaccine – a combination vaccine that protects against whooping cough, diphtheria and tetanus – between the age of two months and six years.
"Most DTaP research has explored vaccine status or decreasing efficacy, but we have looked at both at once," said Ousseny Zerbo, PhD, lead author of the new study and lead investigator at the Vaccine Study. Center of Kaiser Permanente Division Northern California Research.
Dr. Zerbo and his colleagues retrospectively badyzed the electronic health records of 469,982 children under the age of 11 who are members of Kaiser Permanente Northern California. Focusing on data from January 2006 to June 2017, they conducted a series of statistical badyzes to determine the risk of whooping cough based on immunization status and the time elapsed since the last dose given to a child.
The researchers found that the risk of whooping cough was 13 times higher in children who had never received DTaP than in those who had been fully vaccinated with all doses recommended for their age. Under-immunized children – those who had received at least one dose but had fallen behind – were almost twice as likely to develop whooping cough as fully immunized children.
"However, in fully vaccinated children, we found that the risk of whooping cough increased with the time since the last dose," said Dr. Zerbo. Among children aged 19 months to 7 years vaccinated according to their age, the risk of whooping cough was five times higher at more than 3 years of the last dose of vaccine. Notably, most children diagnosed with whooping cough in the study were up to date on DTaP. Of the 738 cases of whooping cough, 603 were fully vaccinated, 99 totally unvaccinated and 36 partially, but late.
These results suggest that in an American population with high vaccination coverage, the decreasing efficacy of DTaP is a determining factor in outbreaks, including the 2010 and 2014 outbreaks in California, each of which resulted in more than 9,000 cases. whooping cough.
"The big question was whether pertussis outbreaks were due to under-vaccination, as in other diseases like measles, or to a decline in immunity," said Nicola P. Klein. , MD, PhD, lead author of the study and director of the Vaccine Study Center. "The answer is that both factors matter."
Further research is needed to quantify the relative roles of decreased immunization and under-vaccination in pertussis outbreaks. Nevertheless, new discoveries point to the need for a better vaccine that lasts longer between doses. At the same time, the authors emphasize that families and clinicians should continue to vaccinate children in accordance with the CDC's recommended schedule.
The researchers pointed out that pertussis rates in vaccinated individuals were lower than those for unvaccinated individuals.
"Despite the increased media attention on the choice of parents not to vaccinate, the children in our study had high coverage, which was not completely surprising," Dr. Zerbo said. One percent of children with pertussis were unvaccinated and 3% were under-vaccinated. "We must continue to encourage immunization, no doubt," he said.
This study is based on a growing number of studies from the Center for Vaccine Studies. New England Journal of Medicine which revealed that protection against whooping cough after 5 doses of DTaP decreased rapidly in school-aged children who received DTaP vaccines only. Next are studies conducted in 2016 and 2017 in pediatrics, one of them showing that systematic reminder of Tdap for adolescents is also decreasing rapidly, and the other showing that Tdap administered to pregnant women was extremely effective in preventing whooping cough in the newborn.
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