Supporting Universal Antenatal Pertussis Vaccination
Pertussis (Whooping Cough) is a serious health issue, especially in the very young infant. It is caused by a bacteria, Bordetella pertussis, and is transmitted person to person via aerosol droplets usually by coughing or sneezing. The illness typically begins with cold-like symptoms which may then progress to the characteristic paroxysms of cough terminating with an inspiratory whoop.
In young infants, the illness can proceed to cyanosis, severe respiratory fatigue, apnea, and even death. Although whole-cell and acellular vaccine formulations against B. pertussis are available, primary immunization generally does not start until 6-8 weeks and as late as 3 months of age in some countries, leaving the infant unprotected during a most vulnerable period.
The incidence of pertussis has steadily increased in the United States and elsewhere since the 1980s and especially since 2005. Since 2010, 10-50,000 cases of whooping cough have been reported each year in the United States with every state represented. More than 48,000 cases were reported in 2012, and in California alone, greater than 10,000 cases were reported in 2014. Although all ages are affected, the highest rates of disease and hospitalization occur in infants less than one year of age. The numbers have been accompanied by an alarming increase in the number of deaths, almost exclusively among infants less than 3 months of age.
One of the causes thought to explain the resurgence of pertussis is the rapid waning of the immunity induced by current vaccines. Prior to the 1990s, a whole-cell vaccine was used and the immunity it induced was longer lasting. Since then, acellular pertussis vaccines have been used exclusively in the United States primarily due to less frequent adverse reactions.
However, these vaccines have been shown to induce immunity which wanes rapidly over a period of several years. As a result, pertussis immunization is required more frequently and the likelihood of non-protection is much greater, especially for older children and adults. This is particularly alarming since such persons are often the caretakers and closest contacts of young infants. Thus, when considering prevention strategies for pertussis, it is critical to include approaches that prevent pertussis transmission to young infants.
In 2001, the Global Pertussis Initiative (GPI) was established in response to the resurgence of pertussis and in an effort to raise global awareness about pertussis and to develop evidence-based recommendations for vaccination strategies . Over the years, the GPI has focused particular attention on protection of the very young infant and has emphasized as a primary strategy maternal immunization during pregnancy which directly protects the infant through the passive transfer of pertussis antibodies from mother to fetus.
Numerous studies have demonstrated that a pregnancy booster (Tdap) provides the necessary protection to the very young from birth until infant-generated immunity is achieved from the primary series of pertussis immunizations. Based on studies that demonstrate robust maternal antibody production within 2 weeks of booster immunization and ready immunoglobulin transfer after 30 weeks’ gestation, current recommendations call for Tdap immunization between 28 and 38 weeks’ gestation.
Since maternal antibody levels decline significantly I year post immunization and are almost non-existent 2 years post immunization, the Advisory Committee on Immunization Practices (ACIP) of the Centers for Disease Control and Prevention (CDC) in 2012 recommended booster immunization during every pregnancy.
To date, research finds that vaccination against pertussis during pregnancy is well tolerated and not associated with any adverse obstetric, birth, or neonatal outcomes. Recently, a study from the United Kingdom evaluating antenatal booster immunization and efficacy in preterm births demonstrated with a mean gestational age of 29 weeks at time of immunization and birth at a mean gestation of 32 weeks, protective antibody levels were found at the start of the primary immunization series.
Unfortunately, despite strong recommendations by the CDC, the American College of Obstetrics and Gynecology, the American Academy of Family Physicians, and the American Academy of Pediatrics , pertussis immunization rates during pregnancy remain very low. Clearly, education of caregivers and patients must be a goal. Until a new pertussis vaccine with longer duration of protection is available, large-scale pertussis outbreaks will continue and the burden of disease will continue to be particularly felt by the very young infant.