Introduction 

Pertussis also known as whooping cough is an infectious respiratory disease caused by Bordetella pertussis. This illness can spread rapidly among humans. When an infected person coughs or sneezes, the droplets which are released into the air are inhaled by the non-infected individuals resulting in the spreading of the disease. In 2018, the World Health Organization reported that the cases of pertussis were above 151000 globally. 

Brief history of pertussis

The organism causing whooping cough (Pertussis) was first isolated in 1906 by Jules Bordet and Octave Gengou. Within 1926-1930, the USA recorded 36,013 deaths due to Pertussis, in this record infants had the highest rates of death. This led to the development of vaccines for the prevention and treatment of whooping cough.¹ 

Symptoms of pertussis

Pertussis comes in the form of a common cold but unlike the common cold, it is continuous, persistent and severe. In the first 2 weeks of having whooping cough patients may present with coughing fits which are uncontrollable and intense lasting for several minutes, this may last up to 6-10 weeks as the case may be. 

There are several other symptoms of pertussis, these include:

1. Runny nose
2. Increase temperature 
3. Vomiting during or after coughing
4. Difficulty in breathing
5. Difficulty in breathing while sleeping
6. Whooping sound (high-pitched sounds) while inhaling after coughing
7. Tiredness after experiencing coughing fits

Transmission of pertussis 

Pertussis is transmitted mainly through droplets produced from coughing and sneezing released into the air. People within breathable space can easily contract this illness.² 

Risk factors of pertussis

Pertussis can easily spread among humans, but some individuals are at a higher risk of contracting Pertussis. The risk factors include:

• Pertussis can be transmitted to people of all ages, with infants below 2 months at more risk. Children can easily contract this infection from older adults and caregivers who have close contact with them³ 
• Underlying ailment: having underlying infections and medical conditions such as HIV, tuberculosis, malnutrition etc, increases the susceptibility of patients to pertussis infection³ 
• Incomplete vaccination: Having less than 3 doses of pertussis vaccine also poses individuals especially infants with potential risks

Complications of pertussis

The complications of pertussis are numerous and these are based on several reports. They include:^4,5

• Pulmonary complications: these involve complications like pneumonia, subcutaneous emphysema, and pulmonary hypertension
• Central nervous complications: this may maybe due to toxins caused by pertussis or inadequate supply of oxygen (hypoxia) due to severe coughing fits. These complications include seizures (more likely to occur in infants than older individuals), inflammation of the brain, encephalopathy, haemorrhage, and hematoma
• Other complications: dehydration, epistaxis, sleep disturbances, fracture, fainting, ear infection, and urinary inconsistency

Immunization in pertussis

The best and most crucial way of preventing pertussis and its life-threatening complications is through immunisation. In 2018, the World Health Organization (WHO) recorded that about 86% of the targeted global population had achieved the recommended three doses of vaccines containing DTP for infants. WHO recommends that the primary dose of vaccination for pertussis begin early at 6 weeks. The DTaP-IPV-Hib vaccine is administered to children at 2, 4, 6, and 12 to 23 months. This is followed by a booster dose of the DTaP-IPV or Tdap-IPV vaccine at 4–6 years and an additional Tdap booster dose at 14–16 years.⁶ 

Immunization schedule

1. For children: for infants between the ages of 2,4,6 and 12 to 23 months, DTap-IPV-Hib- containing vaccine. A booster dose of DTaP-IPV or Tdap-IPV vaccine at age 4-6 years
2. Adolescents: Tdap vaccine is given as a booster dose for teens aged 14 to 16 years
3. Adults: adults in this context are regarded as individuals aged 18 years and above. Adults that have not previously received the Tdap vaccine, are required to take them at least 2 weeks before having contact with infants, as infants are most susceptible to pertussis. Additionally, pregnant women are also recommended to receive a vaccine at 27 and 32 weeks of gestation⁶

Types of vaccine 

The pertussis vaccines are available in two main types, they include the Whole-cell pertussis (wP) vaccine and the Acellular pertussis (aP) vaccine.⁷

• White-cell pertussis vaccine: this vaccine contains the heat-killed (inactivated) Bordetella pertussis. It contains many bacterial antigens and was approved in the 1940s, this helped reduce the incidence of pertussis among children and infants. This type of vaccine is in middle and low-income countries due to their low costs and availability due to ease of production
• Acellular pertussis vaccine: the acellular pertussis vaccine contained the purified components of the inactivated Bordetella pertussis such as the pertussis toxoid (PT), filamentous hemagglutinin (FHA), pertactin (PRN) and fimbriae (FIM)

Pertussis incidence in relation to vaccination coverage

Pertussis is a public health concern and there are increased incident rates in countries with low vaccination rates among their populations. According to a study, pertussis is one of the leading causes of death linked to vaccine-preventable diseases, and such deaths are predominantly among young children who are unvaccinated or have incomplete vaccination.⁸ In 2018, WHO attributed poor vaccination and incomplete vaccination schedules among babies as the leading cause of death in the 151,074 reported cases of pertussis.

Factors influencing immunization effectiveness

There are several factors that influence immunization effectiveness, include:^11,12

1. Individual factor: Factors such as the age of the patient and underlying health conditions have a significant influence on the effectiveness of vaccines against pertussis. For instance, the effectiveness of the Dtap Vaccine decreases with an increase in age and also, children with chronic respiratory pneumonia would show low vaccine effectiveness to pertussis
2. Vaccine factor: factors such as the type of vaccine and the dose of the vaccine received have a positive effect on immunization effectiveness. Studies show that the whole-cell pertussis vaccine is more effective than the acellular pertussis vaccine
3. Health factors: such as having access to healthcare facilities and knowledgeable healthcare providers trigger immunization effectiveness
4. Vaccination policies that promote vaccination availability through increased manufacture and distribution of pertussis vaccines effectively promote immunization
5. Cultural beliefs surrounding vaccine uptake and acceptability increase immunization effectiveness.
6. Children from low socioeconomic backgrounds have decreased vaccine effectiveness, this is due to a lack of access to healthcare facilities
7. Frequent exposure to pertussis reduces the effectiveness of the vaccine for the disease

Impact of low immunization rates

1. Increased incidence of vaccine-preventable diseases: The increased rate of poor vaccination has a direct link to increased incidents of diseases such as pertussis, which can be prevented by being vaccinated and as such lead to increased deaths⁹ 
2. Increased strain on the health system: low immunization can also increase hospitalization and the cost of medical services due to vaccine-preventable diseases. Also, an outbreak of this disease can lead to disruption of normal healthcare services
3. Increased health disparities are a consequence of low immunization thus promoting health inequality within the nation
4. The risk of vaccine-preventable diseases spreading globally is associated with the potential challenges of poor immunization^9,10

Adverse effects of pertussis vaccines

Pertussis vaccines have possible adverse effects which include: anaphylactic reactions, fever, vomiting, loss of appetite, difficulty breathing, and fast heartbeat.¹³

Frequently ask question (FAQ)

What is the difference between the DTap and Tdap vaccines?

DTap vaccines are mainly administered to infants to boost their immunity against diphtheria, tetanus and pertussis and they contain the whole-cell pertussis antigen. Tdap is a booster shot given to teenagers and adults to protect against pertussis, and it contains the acellular pertussis vaccine.

Summary 

Pertussis is preventable and the most effective way to prevent pertussis is through proper vaccination. Vaccination plays a crucial role in the reduction of the transmission of pertussis and the protection of individuals at risk of contracting the disease.