Increase in pertussis linked to nonmedical vaccine exemptions, waning immunity
Data from five U.S. states with a high incidence rate of pertussis revealed geospatial links between nonmedical vaccine exemptions among kindergarteners and illnesses among children and young adolescents.
In addition, Carlin Aloe, of Harvard University Extension School, and colleagues also found evidence of waning immunity with the acellular pertussis vaccine among children aged 10 to 14 years.
“The results suggest that states should reconsider allowing nonmedical vaccine exemptions,” Aloe and colleagues wrote in Proceedings of the National Academy of Sciences of the United States of America. “The data also suggest a need for the creation of a longer acting pertussis vaccine or improved regimen and a revised vaccination schedule for the current acellular pertussis vaccine.”
According to the researchers, the incidence of pertussis began to significantly increase in the United States in the early 2000s, with 48,277 illnesses (15.4 per 100,000 people) reported in 2012 — the highest number reported in the country since 1955. Although the researchers acknowledged that this increase is a multifaceted issue, they set out to better understand the roles of two potential factors: waning immunity and nonmedical vaccine exemptions.
The analysis included county-level data collected in 2012 from Arizona, New Jersey, Oregon, Utah and Washington, all of which had an incidence rate higher than the overall national incidence rate (15.4 per 100,000 people). The researchers searched for statistically significant clusters of nonmedical vaccine exemptions among children entering kindergarten during the 2011-2012 and 2012-2013 academic years and reported pertussis cases among children aged 5 years and younger and young adolescents aged 10 to 14 years.
According to the data, 45% of counties had high rates of nonmedical vaccine exemptions. The researchers identified and geospatially linked eight clusters of nonmedical vaccine exemptions with 11 clusters of pertussis cases.
Further analysis showed that the proportion of kindergarteners with nonmedical vaccine exemptions was 2.8 times larger in the exemption clusters. In addition, high rates of pertussis were identified among children aged 10 to 14 years in 31 counties, indicating waning immunity with the acellular pertussis vaccine, the researchers wrote.
“Although we recognize that correlation does not establish causation, the findings from this investigation are consistent with previous suggestions that geographic clusters of nonmedical vaccine exemptions and waning immunity may have been two of several factors that contributed to community-level pertussis outbreaks,” they concluded.
“It is our hope that these results can help policymakers become more informed regarding decisions about nonmedical vaccine exemptions. The data from this study suggest the need for support for research to develop a more enduring acellular pertussis vaccine or regimen, for strengthening surveillance activities at the local level and for creating an updated vaccination schedule for the current pertussis vaccine, all of which will contribute to better protecting children and communities from vaccine-preventable diseases.” – by Stephanie Viguers
Disclosure: The researchers report no relevant financial disclosures.