Cases of whooping cough, a serious illness in children under one year of age, are on the rise in Spain: should we worry?

In recent weeks, choking cough, a particularly troubling term for parents of minors, is making headlines again in Spain. The trend began in 2023, when the number of cases increased more than nine times compared to 2022. What is the reason for such dramatic growth? Is there any cause for concern?

Whooping cough is a highly contagious disease caused by bacterium Bordetella whooping cough. It is transmitted through direct contact with respiratory secretions or through droplets of saliva from an infected person. The only known hosts are humans.

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The incubation period is usually 7 to 10 days, but can vary from 4 to 21 days. The clinical course is divided into three stages called catarrhal, paroxysmal and convalescent.

The first is characterized by an insidious onset with a runny nose, sneezing, mild cough and symptoms similar to any acute respiratory infection. Then the cough gradually becomes more intense and after 1–2 weeks a paroxysmal phase begins, usually lasting from 1 to 6 weeks. Then typical coughing attacks may occur, making breathing difficult and ending with an effort to inhale (the so-called “rooster”). During these attacks, cyanosis and vomiting may occur.

Finally, during convalescence, the patient gradually gets better. The cough, becoming less paroxysmal, disappears after 2-3 weeks.

Patients with whooping cough can be contagious from the beginning of the catarrhal stage until the third week after the onset of attacks. Vaccinated people may have asymptomatic or mild infection but are able to transmit the disease.

It’s a disease very contagious, as evidenced by secondary cases (up to 80% among household contacts). The source of infection in most cases is household contacts, especially close family members.

Although this disease affects people of all ages, it more serious in children under one year of ageespecially if they have not yet received all doses of the vaccine.

The most common complication is pneumonia. In the United States, it is estimated to account for 13.2% of all cases. Seizures and encephalopathy can also occur as a result of lack of oxygen due to coughing or direct exposure to a bacterial toxin.

Other less serious effects include ear infections, anorexia and dehydration. Finally, increased pressure during coughing attacks can cause pneumothorax, nosebleeds, subdural hematomas, hernias, or rectal prolapse.

A study conducted in Catalonia and Navarre found that 14.9% of cases required hospitalization and 91% were younger than 6 months. In Spain, 91.7% of hospitalizations occur in children under one year of age.

From 2000 to 2006, the national average death rate from whooping cough was one case per year, but from 2007 to 2015, this figure increased to 5.1 per year. In response to this increase, the Interterritorial Council of the National Health System recommended the introduction of a dose of acellular whooping cough vaccine. whooping cough in pregnant women to protect the newborn. During the period 2016-2019, the annual mortality rate from whooping cough decreased to 2.5.

Despite high vaccination coverage, as in other neighboring countries, epidemic waves of pertussis occur every 3–5 years (1998–2001, 2002–2005, 2006–2009, 2010–2013 and 2014–2020).

During the 2020-2022 pandemic, the incidence decreased sharply, but in 2023 the disease began to grow rapidly, which marked the beginning of a new epidemic wave. Based on the behavior of previous epidemics, it is foreseeable that the number of cases will increase until the peak of the wave is reached.

However, vaccinating children and pregnant women prevents serious cases, and the identification of cases and outbreaks by surveillance authorities – especially in the most vulnerable groups – facilitates the implementation of preventive measures that reduce the spread of infection.

We have two measures of action:

• Home isolation of sick people until completion of antibiotic treatment for five days. If they do not receive such treatment, it will continue until they stop coughing or three weeks have passed since the onset of the paroxysmal cough.
• Vaccination. This is an inactivated vaccine that is administered together with others, or as a hexavalent combination (together with components against diphtheria, tetanus, polio, Haemophilus influenzae and hepatitis B); pentavalent (same components, except hepatitis B); quadrivalent (together with the components of diphtheria, tetanus and polio) or trivalent (together with the components of tetanus and diphtheria).

In Europe and North America, acellular vaccines are used, that is, they contain cellular fractions of bacteria that cause the disease, and not the entire pathogen. They cause fewer adverse reactions than whole-cell vaccines: pain and swelling at the injection site or mild fever are the most common.

Not only were cell-based vaccines more likely to cause this type of discomfort, but they also caused seizures and other more severe reactions. Subsequent studies in children over several decades and in different countries confirm the superior effectiveness of acellular vaccines in this aspect.

In Spain, the vaccine is included in the systematic vaccination calendar. It is recommended to prescribe it to children at 2, 4, 11 months and 6 years, as well as to pregnant women in the third trimester of pregnancy, so that they pass on the protection developed in the first months of life to the newborn.

Vaccination coverage in 2022 was 98% for the first three doses, 95% for the 11-month dose and 90% for the 6-year dose. In pregnant women it reached 87%.

Thanks to such high coverage, Why do outbreaks occur that particularly affect teenagers? The answer, at least in part, comes from various studies that have examined the duration of protection provided by acellular vaccines compared with whole-cell vaccines.

According to their results, the risk of contracting whooping cough 5 years after completion of vaccination with acellular vaccinations is clearly higher than that of those immunized with whole-cell preparations.

In addition, the increase in the number of asymptomatic carriers (people who do not get sick but transmit the bacteria) observed among people who received acellular vaccines may contribute to the spread of the disease.

In 2023, 82.7% of Spanish whooping cough cases were vaccinated and more than 5 years had passed since the last dose. The loss of effectiveness of acellular vaccines over time is driving research into new immunization and vaccination strategies that allow us to improve disease control.

Meanwhile, Can we improve immunity against this disease with current vaccines? Available evidence suggests that administering an additional dose during adolescence – as has already been done in Asturias – may be useful in preventing or minimizing outbreaks.

In fact, to counteract the decline in immunity observed over time, most European countries recommend a fifth injection between the ages of 10 and 16 years. In some countries (for example, in Luxembourg and Austria), after expert opinion, they even recommend repeating revaccination every 10 years.

More vaccinations: this is the best answer.

*Angela Domínguez García is a professor of preventive medicine and public health at the Faculty of Medicine, Epidemiology and Public Health, CIBER, University of Barcelona; Pello Latasa, Responsible for Public Health Surveillance, Osakidetza/Basque Health Service; Pere Godoy, physician, professor of public health, University of Lleida.