**4. Clinical aspects**

Clinical presentation is strictly related to the age of acquisition of the infection, the level of immunity, and the use of antibiotic therapy [14].

The disease affects all age groups, especially children, and is one of the most important causes of deaths of <1 year old infants.

The severity of clinical manifestations is inversely related to the age of affected subjects. In children who have not yet been vaccinated, pertussis has a typical course and can lead to major symptoms with severe complications [15]. The prognosis between the first and second year of life is particularly severe, with a high incidence as well as a high number of hospital admissions and deaths (0.2% and 4% lethality rates in developed and developing countries, respectively) [16].

key role in protecting from the disease (as they neutralize bacterial toxins, inhibit the bond between the bacterium and the respiratory tract cells, and allow the capture and destruction of the bacterium by macrophages and neutrophils). Nevertheless, any specific antibody level, against a single antigen or a combination of antigens, which can be related to clinical protec-

Pertussis Immunization in Pregnancy: A Review http://dx.doi.org/10.5772/intechopen.72085 67

Immunity, whether natural or acquired by vaccination, is not long-lasting and tends to decline in a 4–12 years time range. This data is confirmed by the occurrence of epidemics especially in adolescents and adults, even in geographical areas where vaccine coverage is high. Reinfections may occur in adolescents and adults and have been reported in children as well. It is also well known that cell-mediated immunity plays a key role in protecting against infection; the development of this response can be very important in the clearance of the microorganism and in

Although there is a placental transmission of maternal antibodies, most newborns do not appear to be protected against the disease during the first months of life, probably due to the low and inadequate levels of antibody transferred, unless the mother has been recently vaccinated. Several studies on maternal immunization have evaluated its validity, demonstrating

The WHO, in the "position paper" on pertussis vaccination published in 2015 [2], points out that the primary goal of immunization should be to reduce the risk of severe forms in childhood, when morbidity and mortality are particularly high, and indicates 90% as the minimum level of coverage to be achieved with three doses in infants, starting vaccination at 6 weeks of age.

Historically, vaccination is carried out using two types of vaccine: whole or old generation vaccine and acellular or new generation vaccine. Both are mainly used as components of combined products (along with diphtheria and tetanus toxoid) in a 3-dose vaccine schedule.

The whole cell vaccine, consisting of inactivated bacteria, showed a highly variable efficacy (36–96%) and a relatively high reactogenicity in several clinical trials, and for this reason, its wide-scale use was limited [25–27]. The use of the whole cell vaccine may correlate with relatively frequent adverse reactions (AE) (26–40% of doses) such as fever, irritability, reactions at the inoculation site, or more rare AE, such as hypotonia-hyporesponsiveness (1/1500–2000 doses) [28, 29]. The proportion of local reactions tends to increase with the increase of age and of the number of administered doses; for these reasons, whole cell vaccines are not recommended in

Acellular vaccines are less reactogenic [30] and, thanks to their better safety and tolerability profile, their introduction has led to a gradual increase in coverage rates in most Western coun-

However, several studies have shown that the effectiveness of acellular vaccines decreases over time, leading to an increase in pertussis incidence after 8–12 years, even in areas with

tries and, consequently, to a significant reduction in the incidence of the disease.

tion, is currently unknown [21].

the subsequent protection [22, 23].

**6. Available vaccines**

adolescents and adults [29].

an effective antibody-mediated protection of infants [24].

The pertussis incubation period generally lasts 7–10 days, with a range between 4 and 21 days; rarely, it can last up to 42 days. The typical course of the disease is divided into three phases. The first one, called "catarrhal stage," is characterized by the onset of rhinitis, sneezing, fever, and occasional mild coughing. The cough gradually becomes stiffer, and after 1–2 weeks, the second phase, called "paroxysmal stage" begins. Fever is generally low throughout the duration of the disease. It is during the paroxysmal stage that the diagnosis of pertussis can be suspected. Coughing is typical, generally violent, with sudden and paroxysmal attacks, frequently followed by vomiting. It is generally an expression of the difficulty of ejecting the mucus from the tracheobronchial tract. At the end of the paroxysmal attack, a long high-pitched whoop sound or gasp occurs (except in newborns) [17].

Paroxysmal episodes are often followed by physical prostration. In the period between an episode and the other, the subject does not look ill. Paroxysmal attacks occur more frequently at night, with an average of 15 attacks in 24 hours. During the first 1 or 2 weeks of the paroxysmal phase, the attacks increase in frequency, remain stable for another 2–3 weeks and then gradually decrease. The paroxysmal stage usually lasts from 1 to 6 weeks, but can persist up to 10 weeks. In the third phase, "convalescence stage," there is a gradual recovery; paroxysmal cough attacks are less common and tend to disappear in 2 or 3 weeks. However, paroxysmal attacks can occur again, for many months after the onset of pertussis, in the case of concomitant respiratory infections.

The abovementioned description refers to pertussis in its typical form and without therapeutic intervention. Antibiotics significantly improve the clinical picture. The classic presentation of pertussis occurs less frequently even after vaccination [18].

Adolescents, adults, and partially immunized children may have a milder course of disease than babies and infants; the infection can be asymptomatic or can present with symptoms ranging from mild cough to a classical pertussis with persistent cough. Although the disease may be milder in elderly people, such subjects may transmit the infection to other susceptible subjects, including unimmunized or not completely vaccinated infants [19].

The most common complication and cause of death related to pertussis is secondary bacterial pneumonia (about 10% of cases). Neurological complications, such as seizures and encephalopathy, are more common among newborns and may occur as a result of hypoxia or toxin-induced damage. Other less severe complications include otitis media, anorexia, and dehydration. Complications due to paroxysmal attacks include pneumothorax, epistaxis, conjunctival hemorrhage, subdural hematomas, hernias, and rectal prolapse [17, 20].
