Despite high vaccination coverage, a recent increase in pertussis incidence rates has been observed. The objective of the study was to describe epidemiological trends in pertussis between 2012 and 2024 in the Community of Madrid (central Spain).
MethodsPopulation-based observational study of pertussis cases reported to the regional epidemiological surveillance system. The cumulative incidence (CI) per 100 000 person-years was estimated for 2012−2015, 2016−2019, 2020−2022 and 2023−2024, as well as the proportion of hospitalizations and timely vaccination.
ResultsThe cumulative incidence for the age groups 1−4 years, 5−9 years, and 10−14 years were, respectively, 24.4, 16.5, and 15.9 cases per 100,000 person-years in 2012−2015 and 40.1, 62.1, and 58.0 cases per 100,000 person-years in 2023−2024. The cumulative incidence in infants aged less than one year was 243.6 cases per 100,000 person-years in 2012−2015 and 160.1 cases per 100,000 person-years in 2023−2024. The proportions of timely vaccination were 49.4, 89.2, 85.3, 79.1, and 67.2% in the <1, 1−4, 5−9, 10−14, and 15−19 years groups, respectively. The median interval between the last vaccination dose and the onset of symptoms was 3.4 years. In the group of infants aged less than 4 months, 52.2% of mothers had been vaccinated during pregnancy. Five deaths occurred among those infants aged less than 3 months whose mothers had not been vaccinated.
DiscussionDespite the increase in pertussis in older children and adolescents during the 2023−2024 epidemic wave, a remarkable decrease was observed in infants aged less than 6 months. It is necessary to consolidate the vaccination program during pregnancy, ensure timely vaccination and evaluate the age at which the booster is given in adolescence.
Pese a las altas coberturas vacunales, se ha observado un reciente incremento de la incidencia de tosferina. El objetivo del estudio fue describir su patrón epidemiológico entre 2012–2024.
MétodosEstudio observacional descriptivo de base poblacional de los casos de tosferina declarados a la Red de Vigilancia Epidemiológica de la Comunidad de Madrid. Se estimó la incidencia acumulada (IA) por 100.000-habitantes en 2012−2015, 2016−2019, 2020−2022 y 2023−2024, la proporción de hospitalizaciones y la inmunización oportuna.
ResultadosLas incidencias acumuladas para los grupos de edad de 1−4 años, 5−9 años y 10−14 fueron, respectivamente, de 24,4; 16,5 y 15,9 casos por 100.000 hab-año en 2012−2015 y de 40,1; 62,1 y 58,0 casos por 100.000 hab-año en 2023−2024 (última onda epidémica). En menores de un año, la incidencia acumulada fue de 243,6 casos por 100.000 hab-año en 2012−2015 y 160,1 casos por 100.000-hab/año en 2023−2024. Las proporciones de inmunización oportuna fueron de 49,4; 89,2; 85,3; 79,1 y 67,2% en <1,1−4, 5−9, 10−14 y 15−19 años, respectivamente. El intervalo mediano entre la última dosis y el inicio de síntomas fue de 3,4 años. El 52,2% de las madres de casos < 4 meses habían sido inmunizadas en el embarazo. Se produjeron 5 fallecimientos en < 3 meses con madres no inmunizadas.
DiscusiónAunque la onda epidémica 2023−2024 mostró un marcado aumento de incidencia en niños mayores y adolescentes, se observó una notable disminución en menores de 6 meses. Es necesario consolidar la vacunación en gestantes, asegurar una primovacunación oportuna y evaluar la edad de implementación de la dosis de refuerzo en adolescentes.
Pertussis a highly contagious bacterial infectious disease caused by Bordetella pertussis, whose only reservoir is humans. Infants aged less than 4 months are most vulnerable to it and are at risk of serious complications such as apnea, pneumonia, or encephalopathy. In contrast, the disease is generally mild in adolescents and adults, and a persistent cough may be its only symptom, a fact that complicates the diagnosis and facilitates the silent spread of the pathogen.1 There is evidence that older siblings and parents frequently are the main source of infection for infants, with rates of household transmission ranging from 58% to 100% among unvaccinated children.2,3
Although it is well known that vaccine-induced immunity wanes over time,4–6 vaccination remains the most effective preventive strategy for controlling the transmission of pertussis. Routine vaccination with diphtheria, tetanus and whole-cell pertussis vaccine (DTwP) was introduced in Spain in 1965 and replaced by the acellular pertussis trivalent vaccine (DTaP) from 1998. The number of doses progressively increased from 2 to 5 between 1996 and 2001. Between 2011 and 2013, the Community of Madrid (CM) implemented administration of a sixth dose (booster) at age 14 years. Later, the national unified vaccination schedule approved in 2016 established the current vaccination scheme with a primary series consisting of three doses of DTaP given at ages 2, 4 and 11 months, and a booster dose given at age 6 years.7
Vaccination during pregnancy was also introduced in 2016, initially at 36 weeks of gestation and later expanded to 27–36 weeks, preferably between weeks 27 and 28.8 In 2025, following the epidemic wave of 2023−2024, the CM added a booster with Tdap to be given at age 14 years.9
Since 1996, the CM has conducted case-based surveillance of pertussis according to the current protocols.10
Despite high vaccination coverages, in recent years there has been a significant resurgence of pertussis in many countries,11,12 including Spain.13,14 This marked increase has also been observed in the CM.
The aim of our study was to describe temporal trends in the epidemiology of pertussis between 2012 and 2024, analyzing the vaccination status of cases and the associated hospitalizations.
MethodsStudy design, period and settingWe conducted a population-based observational and descriptive study of pertussis cases reported to the Epidemiological Surveillance Network of the Community of Madrid between 2012 and 2024. The case definitions and diagnostic criteria are described in the surveillance protocol of the CM.10
VariablesThe analysis included sociodemographic variables, diagnostic data, vaccination status, complications, hospitalization, death, and other relevant epidemiological data. Clinical information was obtained from an epidemiological survey, supplemented by the review of electronic health records. We determined vaccination status through the vaccination records of the CM. The analysis included vaccine doses administered at least 15 days before the onset of symptoms.
To determine whether cases had been correctly vaccinated, we took into account changes in official vaccination schedules, and harmonized the data in accordance with minimum vaccination requirements: infants aged less than 2 months of age whose mothers had been vaccinated during pregnancy were considered to have been correctly vaccinated; infants aged 2–3 months of age had to have received at least one dose, infants aged 3–11 months at least two doses, children aged 12 months to 5 years at least three doses, and children aged 6 years or older at least four doses.
Statistical analysisWe calculated the cumulative incidence (CumI) in terms of cases per 100 000 inhabitants and by age group, defined both in years (<1, 1−4, 5−9, 10−14, 15−19, 20−39, 40−59 and ≥60 years) and, for the subset of infants aged less than 1 year, also in months (<2, 2−3, 4−5, 6−7, 8−9 and 10−11 months). We obtained data for the reference population from the municipal resident registry for years 2012–2021 and the ongoing census of the National Institute of Statistics from 2022 to 2024.
We grouped the years under study into four periods based on the epidemic cycles and changes in the official vaccination schedule: 2012−2015 (prior to the introduction of vaccination for pregnant women), 2016−2019 (after the introduction of vaccination for pregnant women, pre-pandemic), 2020−2022 (COVID-19 pandemic and post-pandemic, with low pertussis circulation), and 2023−2024 (most recent epidemic wave). We calculated rate ratios (RRs) with the corresponding 95% confidence intervals (CIs) for each period using Poisson regression. The statistical analysis was performed with the software IBM SPSS, version 26.
ResultsIncidence of pertussisBetween 2012 and 2024, there were 4610 reported cases of pertussis in the CM, with epidemic peaks in 2015 and 2024, and a marked decline between 2020 and 2022. A seasonal pattern emerged in years 2012–2019, with increases in incidence between May and July. The seasonal pattern was absent in 2020 and 2021. In the most recent epidemic wave, it occurred earlier, with cases peaking between February and April 2024 (Fig. 1).
The analysis of the CumI by age group in children aged more than 1 year (Table 1) showed that between 2012 and 2015, the CumI was highest in the 1−4 years, 5−9 years, and 10−14 years age groups (22.5, 13.2, and 16.2 cases per 100 000 person-years, respectively). In the years that followed, there was a generalized downward trend. During the 2020−2022 period, the CumI was very low in all age groups. In 2023−2024, there was a generalized increase in the CumI, with the highest rates observed in the 5−9 years and 10−14 years groups (62.1 and 58.0 cases per 100 000 person-years, respectively), followed by the 1−4 years group (40.1 cases per 100 000 person-years). The RRs increased in every age group during the most recent epidemic wave: 1.78 (95% CI, 1.50−2.06) in the 1−4 years group; 4.70 (95% CI, 4.18−5.23) in the 5−9 years group; 3.58 (95% CI, 2.87−4.19) in the 10−14 years group and 8.23 (95% CI, 7.22−9.24) in the 15−19 years group.
Cumulative incidence and incidence ratio by age group for the 2012–2015, 2016–2019, 2020–2022 and 2023–2024 periods in individuals aged more than 1 year and infants aged less than 1 year.
| Age group (years) | CumI 2012−2015 | CumI 2016−2019 | RR 2016−2019/2012−2015 (95% CI) | CumI 2020−2022 | RR 2020−2022/2012−2015 (95% CI) | CumI 2023−2024 | RR 2023−2024/2012−2015 (95% CI) | |||
|---|---|---|---|---|---|---|---|---|---|---|
| Age > 1 year (in years) | ||||||||||
| 1−4 | 22.54 | 24.38 | 1.08 | (0.91−1.25) | 4.19 | 0.19 | (0.10−0.28) | 40.08 | 1.78 | (1.50−2.06) |
| 5−9 | 13.20 | 16.51 | 1.25 | (1.06−1.44) | 1.47 | 0.11 | (0.05−0.16) | 62.07 | 4.70 | (4.18−5.23) |
| 10−14 | 16.20 | 15.93 | 0.98 | (0.79−1.17) | 0.74 | 0.05 | (0.01−0.09) | 58.00 | 3.58 | (2.87−4.19) |
| 15−19 | 1.30 | 2.25 | 1.73 | (1.11−2.36) | 0.48 | 0.37 | (0.17−0.56) | 10.69 | 8.23 | (7.22−9.24) |
| 20−39 | 1.24 | 1.36 | 1.10 | (0.81−1.38) | 0.24 | 0.19 | (0.07−0.32) | 2.02 | 1.63 | (1.03−2.23) |
| 40−59 | 1.19 | 1.85 | 1.55 | (1.29−0.81) | 0.06 | 0.05 | (0.01−0.09) | 3.43 | 2.87 | (1.97−3.67) |
| > 60 | 0.55 | 1.14 | 2.08 | (1.93−2.22) | 0.10 | 0.19 | (0.05−0.35) | 2.17 | 3.96 | (3.10−4.80) |
| Age < 1 year (in months) | ||||||||||
| 0−1 | 466.78 | 191.75 | 0.41 | (0.15−0.67) | 23.13 | 0.05 | (0.01−0.10) | 171.91 | 0.37 | (0.14−0.57) |
| 2−3 | 607.27 | 211.67 | 0.35 | (0.10−0.59) | 26.98 | 0.04 | (0.01−0.08) | 260.83 | 0.43 | (0.22−0.65) |
| 4−5 | 226.59 | 164.36 | 0.73 | (0.53−0.94) | 3.85 | 0.03 | (0.01−0.07) | 136.34 | 0.60 | (0.42−0.81) |
| 6−7 | 83.84 | 109.57 | 1.31 | (0.87−1.74) | 11.56 | 0.14 | (0.06−0.26) | 88.92 | 1.06 | (0.77−1.35) |
| 8−9 | 33.99 | 72.22 | 2.12 | (1.69−2.49) | 7.71 | 0.23 | (0.17−0.56) | 171.91 | 5.06 | (3.68−6.43) |
| 10−11 | 43.05 | 92.14 | 2.14 | (1.62−2.53) | 7.71 | 0.18 | (0.07−0.32) | 130.42 | 3.03 | (3.01−4.90) |
Cases of pertussis notified to the Epidemiological Surveillance Network of the Community of Madrid (2012–2024).
CI, confidence interval; CumI, cumulative incidence per 100 000 inhabitants; RR, rate ratio (relative to the 2012−2015 period).
The incidence was considerably higher in infants aged less than 1 year compared to other age groups throughout the entire study period (Table 1). The analysis of the incidence in infants by age in months revealed a higher CumI in infants aged less than 4 months during the 2012−2015 period, with very high CumI values of 466.8 and 607.3 cases per 100 000 person-years in the 0–2 months and 2−3 months age groups, respectively. Starting in 2016, there was a notable decline in incidence across all age groups, with rates remaining low through 2022. In the 2023−2024 period, the incidence increased in ever age group, but it remained below the rates of the 2012−2015 epidemic wave, especially among infants under 4 months of age, with a CumI of 171.9 and 260.8 cases per 100 000 population-years in the groups aged 0–2 months and 2−3 months, respectively.
The RRs were less than one for infants aged less than 6 months in both the 2016−2019 and 2023−2024 periods compared to the 2012−2015 period, and greater than one for infants aged more than 6 months. In the most recent epidemic wave, the RR for infants under 2 months was 0.37 (95% CI, 0.14−0.57) in relation to 2012−2015. The corresponding RRs for infants aged 2−3 months and 4−5 months were 0.43 (95% CI, 0.22−0.65) and 0.60 (95% CI, 0.42−0.81), respectively. However, in infants aged 8−9 months, the RR in this period rose to 5.06 (95% CI, 3.68−6.43).
Vaccination status of casesOverall, 49.4% of infants with pertussis were correctly vaccinated. The percentage rose to 89.2% for children aged 1−4 years, 85.3% for children aged 5−9 years, 79.1% for children aged 10−14 years, and 67.2% for adolescents aged 15−19 years (Table 2).
Proportion of cases that had been correctly vaccinated by age group (in years and months) and period.
| 2012−2015 | 2016−2019 | 2020−2022 | 2023−2024 | |
|---|---|---|---|---|
| Age < 1 year (age in months) | n (%) | n (%) | n (%) | n (%) |
| 0−1a | 206 (0.0) | 77 (55.8) | 6 (66.6) | 29 (62.1) |
| 2−3 | 268 (45.9) | 85 (61.2) | 7 (42.9) | 44 (59.1) |
| 4−5 | 100 (34.0) | 66 (48.5) | 1 (0.0) | 23 (30.4) |
| 6−7 | 37 (86.5) | 44 (77.3) | 3 (66.7) | 15 (73.3) |
| 8−9 | 15 (73.3) | 29 (89.7) | 2 (100) | 29 (89.7) |
| 10−11 | 19 (89.5) | 37 (100) | 2 (100) | 22 (90.9) |
| Age > 1 year (age in years) | n (%) | n (%) | n (%) | n (%) |
| 1−4 | 259 (89.6) | 256 (83.6) | 30 (80.0) | 173 (93.1) |
| 5−9 | 184 (82.6) | 234 (89.9) | 15 (80.0) | 408 (83.1) |
| 10−14 | 201 (61.7) | 217 (69.1) | 8 (100) | 425 (93.9) |
| 15−19 | 15 (26.7) | 28 (57.1) | 5 (80.0) | 80 (77.5) |
Cases of pertussis notified to the Epidemiological Surveillance Network of the Community of Madrid (2012–2024).
n: total cases notified per age group; %: proportion of cases that had been correctly vaccinated.
There was a growing proportion of cases in infants aged less than 2 months whose mothers had been vaccinated during pregnancy (55.8% between 2016 and 2019; 66.6% between 2020 and 2022; and 62.1% between 2023 and 2024). The proportion of infants aged 4–6 months who were correctly vaccinated was smaller (ranging from 30.4% to 48%). In contrast, the proportion of cases with correct vaccination was higher in infants aged 6–11 months and reached 100% several years.
As regards older age groups, the proportion of children who were correctly vaccinated ranged from 80% to 93% in children aged 1−4 years and 5−9 years. However, the proportion of correctly vaccinated children in the group aged 10−14 years was less than 70% before 2019 and more than 90% afterward. In the group aged 15−19 years, the proportion was low (26.7%) during the 2012−2015 period, increased to 57.1% during the 2016−2019 period, and approached 80% thereafter (Table 2). The median time from the last dose to the onset of pertussis was 41 months (3.4 years), with an interquartile range of 7–70 months (5.8 years).
In the subset of cases in infants aged less than 4 months reported since vaccination of pregnant women was introduced in 2016 (n = 257 cases), 134 mothers had been vaccinated during pregnancy (52.2%), 112 had not been vaccinated (43.6%), and the vaccination status was unknown for the remaining 11 (4.3%). In the group of women vaccinated in 2016, a majority received the vaccine after week 36. Between 2019 and 2022, a higher proportion of mothers received the dose between weeks 32 and 36. In 2023 and 2024, most received the dose before week 32. The proportion of unvaccinated mothers or those with unknown vaccination status declined over time, decreasing from nearly 70% in 2016 to 30% in 2024 (Fig. 2).
We identified several risk factors among the 134 cases in infants younger than 4 months whose mothers had been vaccinated during pregnancy. Specifically, 16 (11.9%) had been born preterm, one (0.7%) extremely preterm, and 12 (9.0%) with low birth weights. No other significant complications at birth had been documented.
FatalityThere were five notified deaths from pertussis were reported (in 2015, 2017, 2020, 2023, and 2024), all of which occurred in infants aged less than 3 months. Four were full-term infants with no underlying medical conditions, and one was a very preterm infant. None of the mothers had been vaccinated against pertussis during pregnancy. Two of the infants had received a single dose of the vaccine, one 5 days and the other 19 days before the onset of symptoms (the latter was the preterm infant).
From a clinical standpoint, there were severe cases with complications such as apnea, pneumonia, pulmonary hypertension, sepsis, and multiple organ failure. Viral coinfection (rhinovirus and/or seasonal coronavirus) was documented in two of the cases, and coinfection by Pseudomonas aeruginosa in one other case.
Hospitalization due to pertussisThe highest percentage of hospitalization was observed in the group of children aged less than 1 year, particularly in 2022 (75.0%) and 2023 (66.7%). The percentage of cases requiring hospitalization was also relatively high in adults aged more than 60 years between 2017 and 2020 (ranging from 20% to 60%) and in 2023 (17.7%) (Table 3).
Proportion of cases that required hospitalization by year and age group.
| Year | <1 year, % | 1−4 years, % | 5−9 years, % | 10−14 years, % | 15−19 years, % | 20−39 years, % | 40−59 years, % | ≥60 years, % |
|---|---|---|---|---|---|---|---|---|
| 2016 | 54.5 | 2.6 | 3.5 | 1.1 | 0.0 | 0.0 | 3.1 | 11.5 |
| 2017 | 52.6 | 8.6 | 1.9 | 2.8 | 25.0 | 3.6 | 7.1 | 20.0 |
| 2018 | 38.9 | 7.2 | 0.0 | 1.8 | 0.0 | 0.0 | 4.7 | 19.2 |
| 2019 | 31.1 | 1.7 | 0.0 | 0.0 | 7.7 | 0.0 | 4.3 | 20.0 |
| 2020 | 53.8 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 60.0 |
| 2021 | 50.0 | 25.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 |
| 2022 | 75.0 | 66.7 | 33.3 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 |
| 2023 | 66.7 | 14.3 | 10.6 | 0.0 | 6.7 | 0.0 | 5.0 | 33.3 |
| 2024 | 40.9 | 4.3 | 1.9 | 1.6 | 4.6 | 1.6 | 6.9 | 17.7 |
Cases of pertussis notified to the Epidemiological Surveillance Network of the Community of Madrid (2016–2024).
Of all infants hospitalized for pertussis in 2023−2024, 55.1% were correctly vaccinated, which constituted an increase compared to 2020−2022 (36.3%) and 2016−2019 (52.2%). In the 1−4 years and 5−9 years age groups, the proportion ranged from 75% to 100%. In the 10−14 years group, the proportion was 100% in the 2016−2019 period and 50% in the 2023−2024 period. In adolescents aged 15–19 years, the proportion remained above 75% (Table 4).
Number and proportion of cases that required hospitalization and were correctly vaccinated, by age group (in years) and period when the case was notified (%).
| Age in years | 2016−2019 | 2020−2022 | 2023−2024 |
|---|---|---|---|
| n (%) | n (%) | n (%) | |
| 0−1 | 161 (52.2) | 11 (36.3) | 76 (55.1) |
| 1−4 | 13 (76.9) | 4 (100) | 11 (81.8) |
| 5−9 | 4 (100) | 1 (100) | 12 (75) |
| 10−14 | 2 (100) | 0 (0) | 6 (50.0) |
| 15−19 | 2 (100) | 0 (0) | 4 (75.0) |
Cases of pertussis notified to the Epidemiological Surveillance Network of the Community of Madrid (2016–2024).
n: number of cases requiring hospitalization by age group; %: proportion of hospitalized cases that were correctly vaccinated.
Pertussis continues to circulate in Spain, as reflected in its seasonal pattern and the occurrence of periodic peaks, which were particularly pronounced during the 2023−2024 season. These findings are consistent with those observed nationwide and in other autonomous communities in Spain,13–16 as well as in neighboring countries.11,12
The incidence of pertussis was highest in infants aged less than 1 year, which was also the group that accounted for all fatalities. However, despite the high circulation of B pertussis among children and adolescents during the 2023−2024 epidemic wave, there was an appreciable decline in incidence in infants under 1 year compared to the previous epidemic wave (2012−2015), specifically in those aged less than 6 months. These findings suggest that the strategy of vaccinating pregnant women has helped protect the youngest and most vulnerable. This phenomenon was also observed at the national level,13,16 although it was not as pronounced.
The goal of vaccination during pregnancy is to prevent maternal infection and transmission to the newborn and to protect the infant through passive antibody transfer. National and international studies have estimated an effectiveness of vaccination during pregnancy of 72%–88%.17–20 Vaccination coverage in pregnant women has been very high since the strategy was first introduced in the CM, ranging from 86.5% to 92.7%, above the national average.21 Furthermore, our study showed that the timing of vaccination during pregnancy has changed over time in adherence to the consensus recommendations on the optimal period for immunization, which is the beginning of the third trimester.22 However, we also found that mothers had not been vaccinated during pregnancy in a significant proportion of cases involving infants younger than 4 months (at least 43.6% of the total). In addition, none of the mothers of the deceased infants had been vaccinated. A recent study identified older maternal age, maternal birth outside of Spain, preterm birth, multiple pregnancy, and home birth as factors associated with lower adherence to the pertussis vaccination program during pregnancy.23 These findings evince the importance of continuing to reinforce this vaccination program.
The vaccination coverage for the pertussis primary series in the CM is very high, and it has remained above 95% since year 2000 and neared 100% since 2016. The coverage for the booster dose has been between 92% and 96% since 2016, values that are very similar to the national average.21 However, in our study, we found that in a high proportion of the cases in infants aged less than 6 months, the infant was not correctly vaccinated, a trend that was disappeared by age 11 months. This finding is very likely due to delays in the administration of the first two doses of vaccine.
The resurgence observed in the other age groups during the 2023−2024 outbreak can be attributed to multiple factors. The waning of immunity over time has been described in numerous studies,5,6 and is mainly attributed to the decreased long-term effectiveness of acellular vaccines compared to whole-cell vaccines.24,25 The average 3- to 4-year interval between the administration of the last dose and the onset of pertussis reflects rapid waning of vaccine-induced immunity.
In addition, several different pertussis strains have been detected in multiple countries in recent years.26 Changes in the antigenic composition of circulating strains have been described as another factor that may be contributing to the resurgence of the disease.27,28 This is compounded by the indirect impact of the COVID-19 pandemic on the transmission dynamics of vaccine-preventable respiratory diseases, with the phenomenon known as the “immunity debt” arising from the drastic decline in the circulation of B pertussis during the pandemic.29,30 On the other hand, during the study period there were changes in the vaccines used for immunization and in vaccination strategies that may have also contributed to the observed trends.
Another factor to consider is the improvement in surveillance systems and the widespread use of diagnostic techniques such as PCR,11,14,24 which has increased diagnostic accuracy. This is reflected in the fact that the proportion of confirmed cases increased from 76% to 88% in infants aged less than 1 year and from 49% to 70% in children aged more than 1 year between 2012 and 2024. It is worth noting that the pathway for sample collection and processing at the Regional Public Health Laboratory has improved significantly, particularly during the most recent epidemic wave (2023−2024), when it was promoted and facilitated by primary care centers.
On the other hand, pertussis is less likely to be suspected with increasing age, which may lead to underreporting of cases in youth and adults. However, the role played by older children and adolescents in the most recent epidemic wave has been clearly demonstrated. This fact has led to the reintroduction of the booster dose for adolescents in January 2025, a practice that was already in place in most European countries.31 Nevertheless, the potential impact of doses administered during adolescence on the incidence in infants aged less than 1 year is still under debate, based on patterns of social interaction.5,32,33 In addition, our study shows high incidence rates in the 10- to 14-year-old group, with a sharp decline from this age. The booster dose for adolescents in Madrid is currently administered at age 14. Advancing its administration slightly to coincide with other scheduled vaccinations at earlier ages could be more efficient to target the most affected age groups, based on the reviewed surveillance findings. There is substantial variation in the time the booster dose is given in other European countries, which ranges between ages 9 and 16 years.31
There are limitations to this study. First, changes in surveillance protocols, data collection methods, response measures, case definitions, and the availability of laboratory tests may have affected the consistency of the data. Furthermore, it is very likely that cases have been underreported, especially among adults, due to a lower level of suspicion compared to the pediatric population, and more specifically during the COVID-19 pandemic, due to disruptions in non-urgent health care services. We were also unable to comprehensively verify vaccination status in adult cases due to the lack of electronic records for vaccines administered in the not-recent past. Furthermore, changes in childhood vaccination schedules affect the number of doses received at a given age by different birth cohorts; therefore, we harmonized the data regarding correct vaccination based on minimum requirements. Finally, the epidemiological surveillance system does not include microbiological information on the circulating strains.
ConclusionsBetween 2023 and 2024, there has been widespread circulation of pertussis, leading to a surge in newly diagnosed cases, particularly in children and adolescents, albeit with a lower incidence among infants. In spite of high vaccination coverages, a significant proportion of cases occurred in infants aged less than 6 months who had not received the number of doses scheduled for their age, and in infants under 4 months whose mothers were not vaccinated during pregnancy. Vaccination coverage in pregnant women and in infants during the first year of life should continue to be monitored, and timely administration of the primary series ensured. Determining the optimal timing for the booster dose in adolescence would also be desirable, preferably taking advantage of appointments for other vaccines included in the official immunization schedule.
FundingThis research did not receive any external funding.
The authors have no conflicts of interest to declare.
