Infant Pertussis: What to Do Next?

E D I T O R I A L C O M M E N TA R Y Infant Pertussis: What to Do Next? C. Mary Healy1,2 and Carol J. Baker1,2,3 1Center for Vaccine Awareness and Research, Texas Children's Hospital; 2Departments of Pediatrics, and 3Molecular Virology and Microbiology, Baylor College of Medicine, Houston, Texas (See the Major Article by Skowronski et al, on pages 318–27.) Received 5 October 2011; accepted 6 October 2011; electronically published 8 December 2011. Correspondence: C. Mary Healy, MD, Section of Infectious Diseases/Department of Pediatrics, Baylor College of Medicine, 1102 Bates St, Ste 1120, Houston, TX 77030 (). Clinical Infectious Diseases 2012;54(3):328–30 Ó The Author 2011. Published by Oxford University Press on behalf of the Infectious Diseases Society of America. All rights reserved. For Permissions, please e-mail: journals. . DOI: 10.1093/cid/cir846 deaths in the United States in the 21st century. The Advisory Committee on Immunization Practice (ACIP) of the Centers for Disease Control and Prevention addressed this public health issue in 2006 by recommending cocooning of infants [9]. Cocooning is the targeted immunization of postpartum women and all contacts of their infants during the first year of life, preferably before theirbirth or hospital discharge. It had been estimated that, when perfectly implemented, cocooning could potentially reduce pertussis cases in infants ,3 months old by 70% [1]. The ACIP recommendation was based on similar proposals in other countries and concurred with the Global Pertussis Initiative view that, notwithstanding the absence of outcome and cost-effectiveness data, cocooning was worth pursuing because ‘‘even protecting just some infants would be considered a success’’ [1]. Implementation of cocooning has been challenging. Logistic and reimbursement issues have hampered hospital and healthcare organizations from immunizing postpartum women with tetanus and reduced diphtheria toxoids and acellular pertussis (Tdap) vaccine. Reports from the few programs implementing Tdap for postpartum women indicate that such programs require an intense focus on parental education and must either have longer than usual windows of opportunity to administer Tdap to 328 d CID 2012:54 (1 February) d EDITORIAL COMMENTARY parents (eg, when infants are admitted to neonatal intensive care units), or innovative strategies with dedicated funding sources and provide vaccine without reimbursement [10–13]. Financial constraints are major barriers to successful cocooning. In this issue of the Journal, Skowronski et al [14] provide one of the first costeffectiveness evaluations of a parental cocooning strategy applied to 2 Canadian provinces, Quebec and British Columbia, both currently experiencing record low rates of pertussis. By use of provincespecific pertussis surveillance trends from 1990 to 2010 and contemporary infant pertussis illness rates, hospitalization data, and mortality data, coupled with infant illness rates attributable to parent exposure and vaccine-effectiveness rates from the literature, they report that immunization of new parents with Tdap (ie, partial cocooning) is expensive and resource intensive in areas where pertussis incidence is low. The number needed to vaccinate exceeds 10 000 to prevent 1 infant hospitalization, 100 000 to prevent 1 infant intensive care admission, and .1 million to prevent 1 infant death. This epidemiologic construct contradicts more optimistic outcome estimates but provides useful data for financially strapped public health agencies. The findings of Skowronski et al [14] are not necessarily applicable to areas experiencing high rates of endemic The resurgence of pertussis during the past 30 years, despite record high immunization rates in infants and children, has led some to label pertussis as the most poorly controlled vaccine-preventable disease in the developed world. The high incidence of pertussis disease in infants too young to be immunized, resulting in substantial morbidity and mortality, is the driving force behind recent prevention strategies [1, 2]. As many as 75% of pertussis-infected infants acquire the disease from a household contact, most often a parent [3–7]. The need for effective preventive strategies was emphasized during the widespread 2010 pertussis outbreak in California. More persons were affected than had been in any single year during the prior 6 decades; the outbreak resulted in an infection rate of 435 cases per 100 000 population in infants ,6 months old and 10 infant deaths, all ,3 months of age [8]. Unfortunately, young infants have accounted for .90% of pertussis-related Interference with antibody responses to other recommended vaccines of varying degrees was noted in all but one study and sometimes persisted into the second year of life [18–20]. Thus, although neonatal immunization is worthy of further investigation, the facts to date appear to limit this approach. Maternal immunization mimics nature’s gift of passive immunity to the newborn infant. Theoretically, achieving high maternal pertussis-specific immunoglobulin G would passively protect the infant for the first few months of life. Anecdotal data from the prevaccine period appear to support this concept [22]. Maternal immunization with whole-cell pertussis vaccine late in pregnancy was reported to be safe for mothers and infants and resulted in high levels of pertussisspecific antibodies in infants. Contemporary studies confirm that active placental transfer of naturally acquired and vaccineinduced pertussis-specific antibodies occurs, and durability of such passively acquired antibody has been demonstrated [23–28]. Despite concerns that high concentrations of maternal antibodies could interfere with the infant’s immune response to active immunization with DTaP vaccine, data suggest that naturally acquired maternal pertussis-specific antibodies do not significantly interfere with an infant’s immune response to active immunization with acellular pertussis vaccines [29]. Although phase 1 maternal Tdap immunization studies are ongoing, these combined data suggest that Tdap immunization in late pregnancy should induce concentrations of maternal pertussis-specific antibodies in the infant that are high enough to protect against pertussis through the period of highest risk, and may be more cost-effective than cocooning. In June 2011, ACIP recommended Tdap immunization in the third or late in the second trimester of pregnancy in preference to cocooning, to prevent pertussis-related mortality in young infants [30]. It was noted that this strategy should be combined with efforts to cocoon the infant by immunizing as many infant contacts as possible, because passively acquired maternal antibodies to pertussis were unlikely to persist in protective concentrations beyond 3 months of age. Furthermore, maternal immunization would probably have little impact on disease rates in preterm infants in whom the risk of mortality (...truncated)