By Rebecca H. Allen, MD, MPH
Assistant Professor, Department of Obstetrics and Gynecology, Warren Alpert Medical School of Brown University, Women and Infants Hospital, Providence, RI
Dr. Allen reports she is a consultant for Bayer.
SYNOPSIS: Prior vaccination of both parents with Tdap (“cocooning”) protects newborn infants from contracting pertussis.
SOURCE: Quinn HE, et al. Parental Tdap boosters and infant pertussis: A case-control study. Pediatrics 2014; Sep 15. Pii: peds.2014-1105 [Epub ahead of print].
In March 2009, amidst a pertussis epidemic, the Australian state of New South Wales initiated a Tdap (tetanus-diphtheria-acellular pertussis) vaccination program free of charge for mothers, fathers, grandparents, and other close adult contacts of infants aged < 12 months. To evaluate the program, researchers conducted a case-control study of 217 infants with pertussis and 585 randomly sampled controls matched by date of birth (¡À 7 days) and “statistical subdivision,” defined as socially and economically homogeneous regions in the state. Cases, collected between April 2009 and March 2011, included infants < 4 months of age with either definitive laboratory evidence (culture or nucleic acid testing) of pertussis or suggestive laboratory evidence (serology) together with a compatible clinical illness (coughing illness lasting 2 weeks associated with paroxysms, inspiratory whoop, or post-tussive vomiting). All cases of pertussis in New South Wales are required to be reported to the Ministry of Health. Parents of cases and controls were interviewed by telephone to ascertain infant history such as breastfeeding, daycare attendance, and vaccination history. All household contacts were identified and the vaccination history of adults was obtained by self report and then confirmed with clinic records when possible (16% of sample). Vaccination status of cases, controls, and siblings was confirmed through the Australian Childhood Immunization Register.
Compared with control households, case households had lower education and income levels, mothers were less likely to have breastfed for more than 2 weeks, and they were more likely to include at least one other child in the home. Overall, similar proportions of mothers reported receiving the Tdap vaccine at any time (76% cases vs 79% controls). However, fewer mothers of the cases had been vaccinated either before pregnancy or after birth but ≤ 4 weeks before the onset of the disease (22% cases vs 32% controls). Case fathers were also less likely to report receiving Tdap at least 4 weeks before the onset of disease (20% cases vs 31% controls). In multivariable analysis, after adjusting for income, education, and number and age of siblings, the protective effect of vaccinating both parents (compared with vaccinating neither) for preventing infant pertussis was 51% (95% confidence interval, 10%-73%). In this analysis, immunizing just the mother or father alone did not result in a statistically significant protective effect.
COMMENTARY
The incidence of pertussis in the United States has been rising with 48,000 cases reported in 2012 and 20 deaths, 15 of which occurred in infants < 3 months of age.1 Indeed, most severe pertussis infections occur in this age group. Given that infants cannot receive the vaccine against diphtheria, tetanus, and pertussis until 2 months of age, they are vulnerable to pertussis after birth. Studies show that newborns often contract pertussis from household contacts, with parents being the source in 50-55% of young infant cases, grandparents in 6-8%, and siblings in up to 20%.2,3 In 2006, the Advisory Committee on Immunization Practices (ACIP) of the Centers for Disease Control and Prevention (CDC) recommended a strategy to prevent neonatal pertussis infection called “cocooning.” In this approach, Tdap was administered to all women in the immediate postpartum period and all other family members and caregivers (who had not received the vaccine) at least 2 weeks before infant contact in order to surround the newborn with a protective “cocoon.”4 This study in Pediatrics provides some of the first field evidence that this approach, if actually implemented, does protect newborns from the disease. While this study has limitations, especially regarding verification of the timing of adult vaccination, it has an adequate sample size and methodology.
In the years after the study period, however, ACIP modified its recommendations to state that women who had not previously received a dose of Tdap should be vaccinated during pregnancy, ideally after 20 weeks of gestation.4 If it was not given during pregnancy, then mothers should still be immunized in the immediate postpartum period and “cocooning” should also be performed. This change was due to challenges in reaching all the adult contacts for vaccination given our fragmented health care system and uptake of the vaccine postpartum was not very high. Unfortunately, pertussis cases persisted in the United States and ACIP recently changed its recommendations again in 2013. With knowledge of the proven safety of adult Tdap vaccination and the fact that immunity does wane significantly after immunization, ACIP now recommends that women receive a dose of Tdap during each pregnancy, irrespective of their prior history.4 Ideally, Tdap should be given between 27 and 36 weeks so that the maternal antibody response and passive antibody transfer to the newborn are maximized. ACIP also reiterated that “cocooning” should still be practiced for the other adults who would have contact with the newborn. Nevertheless, a cost-effectiveness analysis has recently shown that vaccination during each pregnancy is the superior strategy for averting infant pertussis, even more than postpartum vaccination plus “cocooning.”5
While obstetrician-gynecologists do not care for newborns with pertussis, we have an important role to play in preventing the disease. For various reasons, pertussis has resurged in the United States and the world but one main reason is the lower efficacy of acellular vaccines compared to past whole-cell vaccines and the waning immunity after acellular vaccines.6 In fact, it is estimated that vaccine effectiveness lasts only about 2 years after injection. When I first heard the latest recommendations that we need to vaccinate women during every single pregnancy, I was surprised and thought the strategy was overly aggressive. Now, however, I see the logic behind the approach given that pregnant women have access to medical care and vaccinations, immunity wanes rapidly, and this is a sure way to provide protection to infants prior to their own 2-month diphtheria, tetanus, and pertussis vaccination. Although I still think “cocooning” should be encouraged, it is difficult to coordinate a vaccination campaign for an entire family given that each member likely has his or her own medical provider. While this Australian study occurred in the context of free Tdap vaccines for all adults, those types of campaigns are not seen often in the United States. For more information about this issue, the American College of Obstetricians and Gynecologists runs an informative website, www.immunizationforwomen.org.
References
- 2012 Final Pertussis Surveillance Report. Available at: http://www.cdc.gov/pertussis/surv-reporting.html. Accessed Sept. 24, 2014.
- Wendelboe AM, et al. Transmission of Bordetella pertussis to young infants. Pediatr Infect Dis J 2007;26:293-299.
- Bisgard KM, et al. Infant pertussis: Who was the source? Pediatr Infect Dis J 2004;23:985-989.
- ACOG Committee Opinion No. 566 Update on immunization and pregnancy: Tetanus, diphtheria, and pertussis vaccination. Obstet Gynecol 2013;121-1411-1414.
- Terranella A, et al. Pregnancy dose Tdap and postpartum cocooning to prevent infant pertussis: A decision analysis. Pediatrics 2013;131:e1748-e1756.
- Plotkin SA. The pertussis problem. Clin Infect Dis 2014;58:830-833.