An outbreak of whooping cough in Guadalajara, declared this week, has now affected 137 people, most of them between 5 and 13 years of age. No one required hospitalization. This episode is part of a rise in cases observed in Spain and Europe since at least June 2023. In our country, the 2,211 cases detected last year are almost ten times more than the 250 in 2022, and in fact almost double that figure. was reached in the first three years of the pandemic (a total of 1,158 cases between 2020 and 2022), and only the outbreak in La Mancha, which began in December, almost exceeds the total number of cases in 2021 (147). What is the reason for this significant growth?
In fact, comparing 2023 numbers to those in the early years of the pandemic can be misleading. Last year’s numbers are in line with pre-pandemic levels and are a far cry from the 3,503 infections in 2019 and even further from the 9,234 in 2015. The anomaly, therefore, lies in the low number of cases detected in 2020. 2022.
Pediatrician and representative of the Spanish Association of Vaccinologists Fernando Moraga-Llop explains to elDiario.es two factors behind this decline. First, during the Covid-19 crisis, “all respiratory-borne infectious diseases such as RSV and influenza have decreased.” Second, “because the disease does not have a high mortality rate, there were likely many more cases than diagnosed during the pandemic.”
In this sense, the increase in cases observed in recent months will mark a return to pre-pandemic levels. “Many cases have been reported in the last two months. Like everything (diseases caused by respiratory pathogens), we are returning to what we saw before the pandemic,” Moraga-Llop said.
Whooping cough is caused by bacteria Bordetella whooping cough and this does not pose a problem for vaccinated children. Conditions that occur in newborns and children under three months of age who have not yet been immunized can be serious or even fatal. For this reason, since 2016, all autonomous communities have been vaccinating pregnant women: “In this way (the child) will be protected until he receives a dose in two months,” adds the pediatrician.
Why do outbreaks like the one in Guadalajara occur?
Almost every year, outbreaks of whooping cough occur in schools, especially among children 10–12 years of age, although these episodes are usually limited to a dozen cases. The explanation lies in the vaccine, or rather in the lack of a booster dose.
“A primary vaccination is given at two and four months, then a booster is given at 11 months and another at six years, and that’s the end of the story,” Moraga-Llop summarizes. Coverage with this last dose in Spain is around 90%. However, over time, the effectiveness decreases. “Because immunity from current vaccines declines significantly after five years, once children reach 11 years of age, they may become infected.”
The main explanation for outbreaks like the one in Guadalajara is the loss of immunity in students who have been vaccinated for more than five years. In addition to the loss of immunity, it should be added that the vaccine effectively prevents only serious diseases, but not infection. In other words, a vaccinated person can become infected and pass on the bacteria.
“It does not provide sterilizing immunity because it does not create immunity at the mucosal level,” explains Moraga-Llop. For this purpose, intranasal vaccines are being developed that can prevent infection at the site of entry of the pathogen.
What needs to be done?
Pediatricians like Moraga-Llop advocate for another booster dose at around age 14. “Instead of giving the diphtheria and tetanus vaccine, they should also be given the whooping cough vaccine, like the six-year dose,” he comments. In his opinion, this period could even be increased to 11 or 12 years to match the five-year period of the six-year enhancement.
This “doesn’t solve the problem of whooping cough because the teenager will lose immunity at age five and (the bacteria) will continue to circulate, but we will protect the teenager,” he says. This will improve immune protection at school age and reduce outbreaks in educational centers.
Cases of whooping cough can occur at any age, as nine adults infected during the Guadalajara outbreak remember. For this reason, countries such as the United States recommend a dose of diphtheria-tetanus-pertussis vaccine every ten years.
Why did cases start to rise in 2011?
Whooping cough has never disappeared from Spain and Europe, but more than a decade ago there was a change in its epidemiology. To find out the reason for the current increase in whooping cough incidence, we don’t need to look to 2023, but go back to 2011.
“Although the pertussis vaccine has been available for more than 60 years and Spain has achieved high vaccination coverage, both the number of cases and the number of outbreaks have increased in recent years,” write the authors of a study published in 2013 that explained this change.
Moraga-Llop believes one of the factors behind the growth has been improvements in diagnostic tests. “I was then working at the Vall d’Hebron University Hospital in Barcelona, and (the increase in cases) was not detected until 2011, when we started using PCR,” he recalls.
Although whooping cough is a notifiable disease, the doctor emphasizes that many cases in vaccinated children do not “manifest clinically as such” because the disease is “much milder.” These are patients who might have gone undetected in the past, but are now easily detected using the now famous PCR test. This, says Moraga-Llop, does not exclude other factors, such as “genetic changes in bacteria.”
Report published by the National Center for Epidemiology in 2022. supports the pediatrician’s perception. While they explain that the disease has been “in a sustained epidemic situation” in Spain since 2010, they also note that the availability of PCR and awareness in clinical practice have “improved diagnosis and case reporting.” For example, if in 2005 only 25% of cases of infection were confirmed, then in 2011 this percentage exceeded 50%, and at the peak of the maximum incidence in 2015 the percentage reached 84%.