Val d’Hebron: a new variant of whooping cough increases the rise in incidence, which has already led to the death of three babies | Society

Whooping cough, a respiratory infection that particularly affects children, is affecting Spain in a way that has not been seen in decades. According to the latest data from the Carlos III Institute of Health (ISCIII), the current epidemic, which began last June, already has 23,000 cases, hundreds of hospitalizations (mostly of newborns) and the death of three infants. In addition, two elderly people – a 73-year-old woman and an 83-year-old man – also died from the infection, although in both cases they suffered from other serious pathologies that may explain the outcome.

The scale of the outbreak has surprised authorities and experts, and researchers from the Val d’Hebron Research Institute (VHIR, in its Catalan acronym) have now discovered one of the reasons explaining the high numbers: a new variant of the bacterium. Bordetella whooping cough, more evades the defenses of the immune system.

“We wanted to see the reasons for the explosive growth in incidence. We knew that the protection provided by the vaccine wanes over time. In addition, pandemic restrictions have interrupted the circulation of bacteria, so the population has experienced a loss of natural immunity. But we noticed that, in addition, a new transmission line had arisen with characteristics different from those that had been circulating until now. This means that the immune system does not recognize the pathogen well,” explains Juanjo Gonzalez, head of the microbiology research group at VHIR.

The results of this study, awaiting publication in a scientific journal, were presented at a congress that the Spanish Society of Infectious Diseases and Clinical Microbiology (SEIMC) is holding this week in Zaragoza. VHIR studies Bordetella whooping cough and Collections of circulating bacteria have been stored here since the 1980s.

“We saw that bacteria were changing their repertoire of antigens, which are the characteristic protein structures used to make vaccines. Thus, our immune system recognizes them and responds to the pathogen. Changing antigens is an adaptive mechanism that we have now proven has evolved in the microorganism,” adds Gonzalez. This researcher elaborates that “there are three main variants currently circulating” and that the new one is “more similar to those that circulated in the 1980s.”

Cristina Calvo Rey, president of the Spanish Society of Pediatric Infectology (SEIP), emphasizes the “interest and importance” of the VHIR discovery. “The emergence of new strains is typical for infectious diseases; this is an adaptive mechanism of viruses and bacteria. But this study helps explain and allows us to better understand the causes of the major outbreak we are experiencing,” he says.

Whooping cough is highly contagious and is spread through the air through droplets of saliva exhaled when talking and coughing. The infection develops in two phases: the first mild, similar to a respiratory infection (nasal congestion, low fever and mild cough…) and the second, in which the most severe symptoms occur with respiratory and neurological complications that can be fatal in infants. less than six months.

Despite the existence of a vaccine, whooping cough is a disease that cannot be eradicated, experts agree. The drug currently in use is given in five doses: the mother receives the first during pregnancy (preferably at 27 weeks of pregnancy), then the baby receives two injections at two and four months, and another booster at 11 months. and another at age six. Asturias also adds another at 13 years old.

“The main purpose of the vaccine is to protect babies, and in this it is very effective. But other than that it’s not ideal. It loses effectiveness over time and does not prevent vaccinated people from becoming infected or transmitting bacteria… Therefore, repeat doses are necessary, and despite this, outbreaks among older children and adolescents cannot be avoided. However, among them the infection is usually mild,” explains Gonzalez.

According to Josefa Masa Calles, a disease specialist at the National Epidemiological Center (CNE), the latest data obtained by the Carlos III Institute of Health suggests that the current epidemic wave is coming to an end. “We have been receiving fewer case notifications since the end of April,” he says.

If this is confirmed, it will be good news, since the current epidemic has surprised experts not only with its scale, but also with the months in which it has developed. Whooping cough is historically seasonal and occurs in late spring and summer. However, this time during the winter, the number of cases unexpectedly increased sharply. While in 2023 Gipuzkoa was the worst-affected area, in 2024 the most cases were reported in Catalonia, although significant outbreaks also occurred in regions such as Guadalajara.

Masa Calles explains that “this year the Autonomous Communities have reported about 20,000 cases,” to which should be added the almost 3,000 confirmed cases in the second half of 2023. Since 1998, the oldest cases have been included in ISCIII reports, so many infections have never been reported.

Available hospitalization data are still incomplete. In the last months of 2023 there were 124, and this year, of the just over 3,000 cases (one sixth of the total recorded) for which this information is known, there are already 131, so the real number will be several hundred.

The three babies who died during the current epidemic wave have one thing in common: they were unable to benefit from the protection of a vaccine. According to the ISCIII report, the first case, which occurred last year, involved “an infant in the first month of life without risk conditions whose mother was not vaccinated during pregnancy.”

Risk of having premature babies

This year, two – two and three months, respectively – were premature. In one case, the mother was not vaccinated, and in the other, she received the vaccine just five days before giving birth. “Premature babies are a particular risk group because birth may occur before or immediately after the mother’s vaccination, which does not allow time for the baby to develop an immune response and receive antibodies,” explains Masa Calles.

The scale of the epidemic has prompted some participants to call for an extra dose to be added to the vaccination schedule across Spain in adolescence, between the ages of 12 and 14, as Asturias already does. This was recently done by the Vaccine Advisory Committee of the Spanish Association of Pediatrics (AEP). Adolescents are the age group in which the largest number of cases are diagnosed, although at this age they are always mild.

The Vaccine Report expert panel, which advises the Department of Health, discussed the issue at a meeting this week. Sources familiar with the meeting said the additional dose was not considered necessary. “The priority in the fight against whooping cough is to protect the population under six months of age by vaccinating pregnant women and, within the time frame established by the vaccination schedule, the child population,” these sources add.

Vaccination coverage is high in Spain, but experts stress it needs to be increased in situations like the current outbreak. According to the Ministry of Health, in 2022, 87.2% of pregnant women received an anti-whooping cough dose, which simultaneously immunizes the child against diphtheria and tetanus. According to the ISCIII report, 93.3% of infants received their first two doses at two and four months. A recent risk report published by the European Center for Disease Control and Prevention (ECDC) ranked Spain as the top country for the best coverage of pregnant women.