Examining the role of different age groups, and of vaccination during the 2012 Minnesota pertussis outbreak.

Colin J Worby,Edward Goldstein,Ruth Lynfield,Marc Lipsitch,Cynthia Kenyon

doi:10.1038/srep13182

Abstract

There is limited information on the roles of different age groups during pertussis outbreaks. Little is known about vaccine effectiveness against pertussis infection (both clinically apparent and subclinical), which is different from effectiveness against reportable pertussis disease, with the former influencing the impact of vaccination on pertussis transmission in the community. For the 2012 pertussis outbreak in Minnesota, we estimated odds ratios for case counts in pairs of population groups before vs. after the epidemic’s peak. We found children aged 11–12y, 13–14y and 8–10y experienced the greatest rates of depletion of susceptible individuals during the outbreak’s ascent, with all ORs for each of those age groups vs. groups outside this age range significantly above 1, with the highest ORs for ages 11–12y. Receipt of the fifth dose of DTaP was associated with a decreased relative role during the outbreak’s ascent compared to non-receipt [OR 0.16 (0.01, 0.84) for children aged 5, 0.13 (0.003, 0.82) for ages 8–10y, indicating a protective effect of DTaP against pertussis infection. No analogous effect of Tdap was detected. Our results suggest that children aged 8–14y played a key role in propagating this outbreak. The impact of immunization with Tdap on pertussis infection requires further investigation.

Highlights

There is limited information on the roles of different age groups during pertussis outbreaks
While surveillance data provide counts for the numbers of reported cases of pertussis disease in different age groups, those counts may not serve as a reliable indicator of the incidence rates for pertussis infection since the reporting rates for cases of pertussis infection vary by age group due to differences in the severity of disease and disease reporting practices
There is a good deal of uncertainty about the relative magnitude of the incidence rates of pertussis infection in different age groups with the corresponding ambiguity about those groups’ relative role in pertussis transmission in the community

Summary

Introduction

There is limited information on the roles of different age groups during pertussis outbreaks. The resurgence of pertussis (whooping cough) in the past two decades has been the cause of much concern, with the number of reported cases in 2012 in the United States being the highest in fifty years[1] The causes of this resurgence are still not completely understood; in particular, there is uncertainty about the role played by different age groups and the impact of vaccination on the transmission of infection[2,3,4]. In 2005, a booster vaccine (tetanus, reduced diphtheria, and reduced acellular pertussis (Tdap)) was introduced and recommended at age [11,12] years in response to an increasing number of reported cases in adolescents. Given that only a small proportion of pertussis infections are reported[6,18,19], it is important to explore the effectiveness against development of infection to determine the impact of vaccination on pertussis transmission in the community

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