Sharp rise in pertussis hospitalizations highlights need for timely vaccination

Pertussis, commonly known as whooping cough, is a vaccine-preventable disease which continues to circulate even in areas where vaccination coverage is high, and outbreaks may still occur. A study published in Eurosurveillance and conducted at Meyer Children's Hospital in Florence, Italy, has found a sharp increase in hospitalisations for pertussis among children and adolescents (patients aged 16 years or under) in 2024. The findings highlight the critical role of not only adhering to vaccination schedules but also administering doses at the earliest opportunity to ensure a further reduction in cases and hospitalisations among children and adolescents.

Caused by the bacterium Bordetella pertussis, pertussis is a highly contagious respiratory infection that can affect individuals of all ages. While infants (children under one year of age) are most vulnerable to severe disease, recent trends have indicated a shift in the age profile of cases. After several years of low incidence from 2016-2023, Tuscany experienced a sharp rise in pertussis cases in 2024.

The study by Nieddu et al. used retrospective observational data of all pertussis-related hospitalisations from 2016 to 2024. The vaccination status of the participants was taken from a digital vaccination registry in the Tuscany region, which is updated daily by healthcare professionals and vaccination centers. For each patient, the time interval between the first eligible day for vaccine administration (when the vaccine could have been administered but was not) and the onset of disease was calculated. From this, the delay was calculated from the number of days between the eligible vaccination date and disease onset.

A ninefold increase in cases since 2016-2019

Between January and December 2024, 259 children and adolescents were hospitalised with laboratory-confirmed pertussis. Compared with data from 2016-2019, there was a ninefold increase in admissions of children and adolescents during the 2024 period. Of note, over half of these cases occurred in adolescents aged 10–16 years, while infants accounted for just 7% of cases. This contrasts with earlier outbreaks, where infants represented the majority of hospitalisations.

Timeliness of vaccination as essential as coverage

Tuscany has one of the highest pertussis vaccination rates in Italy, with 97.7% of two-year-olds and 75.8% of 16-year-olds being fully vaccinated. However, the study outlined that many patients had received their doses at the latest point in time within the recommended schedule. Among infants eligible for vaccination, delays averaged more than a month for the first three doses. For adolescents, the gap between eligibility for the booster (recommended from age 12) and disease onset often exceeded a year.

"Formal compliance with the schedule is not enough", the authors note. "Timely administration could have prevented many hospitalisations".

Most adolescents in the study had completed their early childhood vaccinations suggesting a waning immunity rather than vaccine refusal as the main driver for the increase in cases. The current Italian schedule allows the adolescent booster to be given anytime between 12 and 18 years, a window which this study suggests may be too wide.

Among infants too young to receive their first dose of pertussis vaccine (77 patients were younger than 1 year and 20 were younger than 2 months), none of the mothers had received the recommended pertussis vaccine during pregnancy, despite its availability free of charge across Italy. This highlighted another missed opportunity for protection.

Public health implications

According to the authors, these findings call for renewed public health messaging emphasising not just the importance of vaccination but also that it be done in a timely manner. Strategies could include reminders for families and healthcare providers, as well as campaigns to reduce vaccine hesitancy and vaccine fatigue. Strong and robust surveillance systems are also essential to detect and respond to emerging trends.

The authors conclude that to mitigate resurgence of pertussis and prevent future outbreaks, a combination of measures should be implemented such as "strict adherence to the immunisation schedule, prioritising administration of vaccines at the earliest eligible opportunity, and consideration of advancing the adolescent booster dose".