Friday, June 10, 2016

Pertussis: waning immunity and Tdap during pregnancy

I've written several posts on pertussis (whooping cough) and pertussis vaccines over the last four years. I started my position in communicable disease epidemiology at the Tacoma-Pierce County Health Department at the beginning of the 2012 Washington State pertussis epidemic. Pertussis is a issue that has demanded a lot of our time and attention ever since.
This is an article that I wrote for our Communicable Disease and Immunization Update newsletter:
Historically, pertussis was thought of as a childhood disease. We now recognize that immunity to pertussis, through immunization or natural infection, wanes over time, and that the effectiveness of acellular pertussis vaccines wanes much more quickly than immunity from whole-cell pertussis vaccines. A case-control study reviewing data from the 2012 pertussis epidemic in Washington State demonstrated that, for children who had received all acellular pertussis vaccines, vaccine effectiveness was 73.1% within one year, 54.9% between one and two years, and 24.2% between two and three years (Acosta et al., 2015). Two studies of data from the 2010 pertussis epidemic in California demonstrated that children who received one or more doses of whole-cell pertussis vaccine were less likely to have polymerase chain reaction (PCR)-confirmed pertussis than children who had received all acellular pertussis vaccines (Klein et al., 2013; Witt et al., 2013).
The age distribution of pertussis cases in Pierce County in 2012 was similar to that in California in 2014 (Winter et al., 2014), with fewer cases at the ages at which pertussis vaccine booster doses are scheduled and fewer cases and lower incidence of pertussis in people born before 1997 who would have received at least one dose of whole-cell pertussis vaccine as part of their primary series.
Infants too young to receive pertussis-containing vaccine are at highest risk for complications and death from pertussis. During the 2012 epidemic, the incidence of pertussis in Pierce County and Washington State was highest in children under one year of age. Of the 15 Pierce County residents hospitalized for pertussis in 2012, 12 (80%) were under one year of age and 11 of those were under 6 months of age, too young to have received 3 doses of DTaP.
In 2015, 5 Pierce County residents were hospitalized for pertussis, three of whom were infants less than 2 months of age. Two of the mothers of those babies did not receive the recommended dose of tetanus, diphtheria, and acellular pertussis vaccine (Tdap) during pregnancy.
Case Series:
Case 1: Two-month-old girl with worsening cough admitted for observation with PCR-confirmed pertussis. Her mother received Tdap during pregnancy. While hospitalized, the infant had mild desaturations during coughing fits which quickly resolved without intervention. The baby was observed on the pediatric unit, not intensive care unit (ICU), and was discharged home on day three.
Case 2: One-month-old girl admitted with repeated episodes of desaturation and bradycardia. On the second day after admission, the baby was intubated and mechanically ventilated with sedation and chemical paralysis. She spent 8 days intubated, 11 days in the pediatric intensive care unit (PICU), and was discharged to home on day 15. Her mother did not receive Tdap during pregnancy.
Case 3: Three-week-old girl admitted after an episode of choking cough, apnea and cyanosis. Although the obstetric care provider recommended that her mother get a Tdap at the pharmacy, she did not receive one. The baby spent 3 weeks in PICU and was discharged four weeks after admission.
Although this sample is not representative, it is notable that the child whose mother received Tdap during pregnancy was not admitted to the PICU and had the shortest length of stay.
Antibody titers in adults who receive Tdap also wane. Healy et al. (2013) found that titers of pertussis-specific antibodies in cord blood from mothers who had received Tdap before or early in pregnancy were unlikely to provide adequate protection against infection for their newborn infants. In October 2012, the CDC's Advisory Committee on Immunization Practices (ACIP) recommended Tdap at 27 to 36 weeks of gestation with every pregnancy based on studies of paired maternal and cord blood from women who received Tdap during pregnancy. The American College of Obstetricians and Gynecologists (ACOG) and the American College of Nurse-Midwives support the ACIP recommendation.
Two studies conducted in the U.K. evaluated the effectiveness of maternal Tdap at preventing pertussis in infants too young to receive DTaP. Vaccine effectiveness was 93% for infants born to women who received Tdap in the third trimester (Dabrera et al., 2015) and 90% for infants younger than 2 months whose mothers received Tdap at least 1 week before birth (Amirthalingam et al., 2014).
Although estimates since the 2012 recommendation have not yet been published, uptake of Tdap during pregnancy has been lower than optimal. As part of a pilot project, the Washington State Department of Health is currently collecting data on Tdap during pregnancy from hospitals in selected counties, including Pierce. Data are preliminary, but, in 2014, less than 50% of women who delivered at Pierce County hospitals had a dose of Tdap during the pregnancy that was recorded in the hospitals' electronic medical record. Administering Tdap during a prenatal visit is the most effective way to ensure that a pregnant woman receives the dose. CDC recommends that providers who do not stock vaccines in their offices make a "strong referral" for vaccination. Resources supporting immunizing pregnant women are found on the ACOG, CDC, and Tacoma-Pierce County Health Department websites.

Acosta, A. M., DeBolt, C., Tasslimi, A., Lewis, M., Stewart, L. K., Misgades, L. K., et al. (2015). Tdap vaccine effective in adolescents during the 2012 Washington State pertussis epidemic. Pediatrics, 135(6). doi:10.1542/peds.2014-3358.
American College of Nurse-Midwives. (2014). Position statement: immunization in pregnancy and p.ostpartum.
American College of Obstetrics and Gynecologists. (2013). ACOG Committee Opinion No. 566: Update of immunization and pregnancy: tetanus, diphtheria, and pertussis vaccination. Obstetrics and Gynecology, 121(6). doi:10.1097/01.AOG.0000431054.33593.e3.
Amirthalingam, G., Andrews, N., Campbell, H., Ribeiro, S., Kara, E., Donegan, K., et al. (2014). Effectiveness of maternal pertussis vaccination in England: an observational study. Lancet, 384(9953). doi:10.1016/S0140-6736(14)60686-3.
Centers for Disease Control and Prevention. (2013). Updated recommendations for use of tetanus toxoid, reduced diphtheria, and acellular pertussis vaccine (Tdap) in pregnant women – Advisory Committee on Immunization Practices (ACIP), 2012. Morbidity and Mortality Weekly Report, 62(7), 131-135.
Dabrera, G., Amirthalingam, G., Andrews, N., Campbell, H., Ribeiro, S., Kara, E., et al. (2015). A case-control study to estimate the effectiveness of maternal pertussis vaccination in protecting newborn infants in England and Wales, 2012-2013. Clinical Infectious Diseases, 60(3). doi:10.1093/cid/ciu821.
Edwards, K. M. & Decker, M. D. (2013). Pertussis vaccines. In S. A. Plotkin, W. A. Orenstein, & P. A. Offit (Eds.) Vaccines (6th Ed.). [Electronic version]. Elsevier.
Healy, C. M., Rench, M. A., & Baker, C. J. (2013). Importance of timing of maternal combines tetanus, diphtheria, and acellular pertussis (Tdap) immunization and protection of young infants. Clinical Infectious Diseases, 56(4). doi:10.1093/cid/cis923.
Klein, N. P., Bartlett, J., Fireman, B., Rowhani-Rahbar, A. & Baxter, R. (2013). Comparative effectiveness of acellular versus whole-cell pertussis vaccines in teenagers. Pediatrics, 131(6). doi:10.1542/peds.2012-3836.
Winter, K., Harriman, K., Zipprich, J., Schechter, R., Talarico, J., Watt, J., et al. (2012). California pertussis epidemic, 2010. Journal of Pediatrics, 161(6). doi:10.1016/j.jpeds.2012.05.041.
Witt, M. A., Arias, L., Katz, P. H., Truong, E. T., & Witt, D. J. (2013). Reduced risk of pertussis among persons ever vaccinated with whole cell pertussis vaccine compared to recipients of acellular pertussis vaccines in a large US cohort. Clinical Infectious Diseases, 56(9). doi:10.1093/cid/cit046.

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