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Pertussis disease rates and the role of Tdap vaccines
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Immunization schedules targeting infection and illness from Bordetella pertussis have been in place in the United States for more than 50 years, but pertussis remains problematic as a major vaccine-preventable disease.
The United States has experienced recent epidemics of pertussis, in 2005 and 2010, and the incidence of pertussis continues to remain high in 2012. The CDC reports that since 2004, a mean of 3,055 cases of pertussis disease and 19 deaths have occurred annually in young infants (aged 2 months and younger). In 2010, 27,550 cases of pertussis occurred in children and adults in the United States. Several purified acellular-component pertussis vaccine products (DTaP) are available for the pediatric immunization schedule and their use is relatively high — 83.9% for at least four doses (2009). These purified products replaced older whole-cell vaccine products 15 years ago. Although the acellular vaccines are less reactogenic than the whole-cell vaccines they replaced, their efficacy is decreased. The newest pertussis vaccines, reduced-dose acellular products (Tdap), were introduced 7 years ago and include Adacel (Sanofi-Pasteur) and Boostrix (GlaxoSmithKline). The role and frequency of administration of these relatively new products are currently undergoing active study and are likely to play a significant role in future strategies to control pertussis.
Increased incidence
It is likely that a combination of factors is responsible for the recent increase in reportable pertussis in children and adults. Although immunization against pertussis has been utilized in clinical practice for many years, problems remain with its use. Immunity to pertussis from natural infection and immunization wanes with time and is not life-long, as is other infectious diseases for which we have vaccines. Although the currently available acellular-component pertussis vaccines are generally effective and safe, several studies have demonstrated that they are less effective than the older whole-cell vaccines.
Edward A. Bell
Morbidity and mortality from pertussis is highest in young infants — infants aged younger than 12 months — and especially among infants aged younger than 2 months. With the first dose of DTaP recommended at age 2 months by the 2012 pediatric immunization schedule, the youngest infants remain the most susceptible. Published studies have documented that the major source exposing susceptible infants to B. pertussis is household adults, namely mothers, fathers and other family members.
Several studies have documented such family members to be the sources of infection in 76% to 83% of infants. Adults may harbor B. pertussis manifesting as asymptomatic infection, or they may be symptomatic with cough illness. Several studies have shown that 13% to 20% of cough illness in adolescents and adults is caused by B. pertussis . Additional published information has shown that pertussis in adults is often misdiagnosed and, subsequently, mistreated. This information has led to newer strategies of attempting to control infection and illness in adults. Besides these therapeutic-related causes, increased awareness and reporting of pertussis and improved diagnostic techniques have additionally led to increased incidence of reportable pertussis.
Use of Tdap in adolescents and adults
Two Tdap products are currently available for use in adolescents and adults, Adacel (labeled for use at ages 11 to 64 years) and Boostrix (labeled for use at ages 10 years and older). The AAP recommends that Tdap preferably be given at 11 to 12 years. Utilization of these vaccines, however, is not high — 68.7% among adolescents (2010) and only 8.2% among adults (2010).
Several additional strategies for decreasing pertussis morbidity and mortality have been recommended. In 2011, the Advisory Committee for Immunization Practices recommended that pregnant women who had not previously received Tdap be offered it during pregnancy to allow transfer of maternal antibodies to the fetus and subsequently to the infant upon birth. The preferable time for immunization is the third trimester or late second trimester (after 20 weeks of gestation). If immunization at this time does not occur, it is recommended that Tdap be offered immediately postpartum.
Vaccinating a young infant’s (aged younger than 12 months) adolescent and adult family members and close contacts with Tdap, including the mother immediately after birth (if a negative history of Tdap administration during pregnancy), is also recommended, a strategy known as cocooning. Ideally, Tdap should be given 2 weeks before known infant contact. The AAP and CDC recommend cocooning, although its effectiveness can be limited by logistical and practical considerations.
A unique additional strategy that has recently been discussed in the medical literature is immunization of adult family members in the pediatric inpatient and ambulatory settings. Several studies have evaluated the administration of influenza vaccine and Tdap to parents and guardians of newborn infants and have reported limited success. In 2012, the AAP published a report describing the immunization of parents and family contacts in the pediatric office setting as an additional strategy to protect young infants from vaccine-preventable diseases, such as pertussis.
Role for clinicians
Following the annual pediatric immunization schedules as published by the ACIP and AAP remains the most important strategy for protecting infants and children from vaccine-preventable diseases. Despite relatively high rates of DTaP administration, however, morbidity and mortality from pertussis is increasing. More effective primary series vaccines are needed, as are other strategies to control pertussis. Tdap vaccines are underutilized, especially among adults. Utilization of Tdap by adolescents is higher, although there is room for increased use. Most importantly, pediatricians can discuss these issues with their patients and families and provide education on the clinical benefit of Tdap administration. Although more research is needed, some data indicate that vaccinating parents directly in the pediatric ambulatory and inpatient setting can offer additional protection to young infants.
For more information:
- CDC. MMWR. 2011;60(33):1117-1123.
- CDC. MMWR. 2011;60(41):1424-1426.
- CDC. MMWR. 2012;61(4):66-72.
- Cherry JD. N Engl J Med. 2012;367:785-787.
- Cherry JD. Pediatrics. 2012;129:968-970.
- Lessin HR. Pediatrics. 2012;129:e247-e253.