Annual theme 2025: vaccine-preventable diseases in humans

A surge in pertussis occurred in the Netherlands in 2023–24. Infant vaccination uptake decreased from 95% in 2011 to ca 86% in 2024. Maternal vaccination was introduced in 2019, with uptake ca 70%.

To describe pertussis epidemiological trends in the Netherlands.

We conducted a retrospective study using pertussis notification data from 2012 to 2024 and estimated infant and maternal vaccine effectiveness (VE) with the screening method.

During the COVID-19 pandemic, pertussis notifications dropped from ca 6,000 in 2013–19 to 79 in 2021 (incidence ca 35 to < 0.01/100,000 population). Notifications surged from May 2023, peaking in March 2024, resulting in 18,208 notifications in 2024 (102/100,000). Notifications and hospitalisations in 2024 were highest among infants aged 0–5 months (573 and 304/100,000) followed by infants aged 6–11 months (446 and 92/100,000). Annually, 0–2 deaths were reported; in 2023–24, 10 deaths were reported (6 infants, 4  ≥ 60-year-olds). In 2024, 83% of mothers of notified infants aged 0–2 months were unvaccinated. In 2020–24, maternal VE against pertussis in infants aged 0–2 months was 91%. In 2012–24 primary series VE was 98% at age 1, 92% at age 3, 92% post-booster at age 5, and 71% at age 9 years.

Low population immunity after 2 years of reduced circulation likely contributed to the highest pertussis incidence ever recorded in the Netherlands, posing a particular threat to unprotected infants. Maternal and infant VE are high, underscoring the public health priority of enhancing vaccination uptake.

Global resurgence of measles highlights the need for countries to identify and address immunity gaps. This is challenging given antibody waning and, in Ireland, the absence of robust national vaccine coverage data, population changes due to migration and outdated population-level seroprevalence data from the last national serosurvey (2003).

We aimed to determine the seroprevalence of measles IgG in children aged 3–17 years in Ireland.

Convenience sampling of anonymised residual serum samples from four hospital laboratories across four of six health regions was conducted between 1 February and 19 June 2024. Samples were tested for measles IgG antibodies using a commercial chemiluminescence immunoassay. Seropositivity was adjusted for test sensitivity and specificity and was calculated by sex, age and location.

In total 2,509 of 2,924 samples were seropositive and 415 were seronegative indicating measles IgG seroprevalence of 90.3% (95% confidence interval (CI): 89.2–91.4), with no significant difference by sex. Children aged 3–5 years (94.9%; 95% CI: 92.4–96.6) and 6–9 years (94.2%; 95% CI: 91.7–95.9) had significantly higher seropositivity when compared with children aged 10–13 years (89.1%; 95% CI: 86.6–91.3) and 14–17 years (87.6%; 95% CI: 85.5–89.4).

Our findings suggest close to adequate protection against measles among children 3–9 years but suboptimal (< 95%) protection among children aged 10–17 years. This immunity gap is not reflected in measles vaccine coverage data, highlighting the utility of seroprevalence data to enhance knowledge of clinical protection at population level and to inform vaccination strategies.

Pertussis remains a serious threat to young infants. In Norway, infants receive an acellular pertussis vaccine (aP) according to a 2 + 1 schedule at 3, 5 and 12 months of age, delivered as a hexavalent vaccine.

We aimed to study susceptibility to pertussis in mothers and infants to guide decisions regarding vaccination in pregnancy.

In this prospective observational study, we included 366 mother/infant pairs during 2020–2023, collecting blood samples from mothers in late pregnancy, cord blood at delivery and from infants before their first and after their third vaccine dose. We retrieved health registry data on vaccination and pregnancy-related information. IgG antibody levels against pertussis-antigens, diphtheria and tetanus were measured using a multiplex immunoassay.

Of the pregnant women, 48% (174/366) had low levels of antibodies against pertussis toxin (PT) defined as below 5 IU/mL. Maternal antibodies declined in infants from birth until first vaccination, leaving 72% (154/215) of infants with anti-PT IgG levels below 5 IU/mL. All infants responded well to vaccination and we found no evidence of blunting from high levels (> 40 IU/mL) of maternal antibodies against PT. Infants of mothers who received an aP-containing booster vaccine within 2 years before pregnancy displayed low anti-PT IgG levels, with 58% (15/26) having levels below 5 IU/mL.

A high proportion of pregnant women and their infants under 3 months of age had low anti-PT antibody levels, indicating high susceptibility to pertussis. The results support the introduction of vaccination against pertussis during pregnancy in Norway.

Rotavirus is a main gastroenteritis cause in children ≤ 5 years old. In 2017, when few Italian regions had rotavirus vaccination programmes, rotavirus vaccines were included in the National Plan for Preventive Vaccination (PNPV). Although all Italian regions follow the PNPV, they each decide how to implement it, contributing to rotavirus vaccination coverage differences across the country.

The objective was to assess rotavirus vaccination national/regional policies in Italy and, between 2016 and 2023, vaccination coverage trends at national and regional level.

Scientific and grey literature was systematically reviewed for reports on Italian national/regional policies or programmes concerning rotavirus vaccination. Their key features and strategies to increase vaccination coverage were recorded. Vaccination coverage data originating from the Ministry of Health, were analysed descriptively, or with linear regression, for national and regional trends.

Among 418 policy/programme reports identified, 25 were included. Between 2013 and 2015, Sicilia, Calabria and Puglia had already initiated universal vaccination programmes. The PNPV 2017–19 standardised regions’ offer of rotavirus vaccination. Between 2016 and 2023, vaccination coverage in Italy significantly increased (p = 0.0005) from 10.5% to 70.76%, with a 140% rise in 2019−20. Regional coverage disparities existed. Throughout 2016–23, most central Italian regions had annual coverages below national values. Bolzano annual coverage was consistently < 50%, while in Veneto, coverage reached 85.10% in 2021. In 2023, five regions had > 80% coverage.

While rotavirus vaccination coverage improved in Italy in 2016−23, regional disparities persist. Addressing these requires overcoming logistical and societal challenges, as well as harmonised policies.

Childhood vaccination coverage has declined in recent years in many countries, including the Netherlands.

To understand differences in coverage between population subgroups in the Netherlands over time, we studied sociodemographic factors associated with measles–mumps–rubella (MMR) and diphtheria–tetanus–pertussis–poliomyelitis (DTaP-IPV) vaccination.

We conducted a national retrospective database study including children born between 2008 and 2020. Individual-level data linkage allowed examination of associations of sociodemographic variables with MMR and DTaP-IPV vaccination status at age 2 years. We calculated coverage for each variable, stratified by birth cohort. Multivariable Poisson regression assessed independent associations and changes in coverage over time.

MMR coverage decreased in all population subgroups (overall 95% in cohort 2008 and 89% in cohort 2020), more substantially in some. In multivariable analysis, children of non-Dutch origin, particularly Moroccan and Turkish origin, showed more pronounced declines (respectively −25% and −12% as children of Dutch origin in cohort 2020). Among children not attending daycare and children living in larger families (≥ 4 children), coverage declined faster than in those attending daycare and living in smaller families (both −12% in cohort 2020). Coverage among children of self-employed mothers and children in the lowest income households was lower than among children of mothers in employment and the highest income households (respectively −8% and −7% in cohort 2020). Trends for DTaP-IPV vaccination were nearly identical.

Childhood vaccination coverage in the Netherlands declined substantially, with increasing disparities between sociodemographic groups. Vaccination efforts should be prioritised to protect public health equitably.

Influenza A(H1N1)pdm09, A(H3N2) and B/Victoria viruses circulated in Europe in 2023/24, with A(H1N1)pdm09 dominance. First influenza infections in childhood may lead to different vaccine effectiveness (VE) in subsequent years.

The VEBIS primary care network estimated influenza VE in Europe using a multicentre test‐negative study.

Primary care practitioners collected information and specimens from patients consulting with acute respiratory infection. We estimated VE against influenza (sub)type and clade, by age group and by year of age for A(H1N1)pdm09, using logistic regression.

We included 29,958 patients, with 3,054, 1,053 and 311 influenza A(H1N1)pdm09, A(H3N2) and B cases, respectively. All-age VE against influenza A(H1N1)pdm09 was 52% (95% CI: 44–59). By year of age, VE was 27% (95% CI: −2 to 47) at 44 years with peaks at 72% (95% CI: 52–84) and 54% (95% CI: 41–64) among children and those 65 years and older, respectively. All-age A(H1N1)pdm09 VE against clade 5a.2a was 41% (95% CI: 24–54) and −11% (95% CI: −69 to 26) against clade 5a.2a.1. The A(H3N2) VE was 35% (95% CI: 20–48) among all ages and ranged between 34% and 40% by age group. All-age VE against clade 2a.3a.1 was 38% (95% CI: 1–62). All-age VE against B/Victoria was 83% (95% CI: 65–94), ranging between 70 and 92% by age group.

The 2023/24 VEBIS primary care VE against medically attended symptomatic influenza infection was high against influenza B/Victoria, but lower against influenza A(H1N1)pdm09 and A(H3N2). Clade- and age-specific effects may have played a role in the lower A(H1N1)pdm09 VE.

Vaccine-derived polioviruses (VDPVs) continue to circulate internationally, causing sporadic cases and outbreaks of paralytic polio in countries certified as polio-free. In 2022, sustained detection of type 2 VDPVs was reported in environmental surveillance samples collected from London. Genetic mutations indicative of loss of attenuation of virulence were observed, consistent with community transmission events over several months.

We aimed to determine the extent of geographical spread of transmission in an area of environmental poliovirus detection.

We implemented an opportunistic, cross-sectional survey in areas where environmental surveillance indicated sustained VDPV transmission between October 2022 and April 2023. Residual stool samples taken from children < 16 years presenting to primary or secondary healthcare were examined for enteroviruses, including poliovirus. Methods for poliovirus detection recommended by the World Health Organization, including virus isolation in cell culture, PCR and molecular characterisation, were applied to residual stool material on a daily basis with real-time clinical reporting.

We examined 1,251 stool samples from 1,051 children presenting to healthcare with illness over a 6-month period. A range of enteroviruses from groups A, B and C were found, but no poliovirus was detected. Documented polio vaccination coverage was high, between 95% and 98% in under 5-year-olds.

Poliovirus was not widespread in the area of environmental poliovirus isolation. Opportunistic poliovirus testing of residual stool samples taken from children seeking healthcare was feasible and can be implemented rapidly in areas where poliovirus circulation is suspected, although untargeted sampling may not adequately capture populations at highest risk.

Vaccination programmes initiated in the early 1970s reduced the incidence of measles in Austria, which resulted in the interruption of endemic measles virus (MeV) circulation and the achievement of elimination status in 2018. However, large outbreaks occurred in 2023 and 2024.

By assessing MeV-specific IgG antibody levels, we analysed if immunity recently declined due to the COVID-19 pandemic, vaccine-induced immunity waned over long term or immunity gaps already pre-existed in the population.

We determined anti-MeV antibody levels in a retrospective dataset of 56,360 diagnostic samples (from 50,754 individuals) collected 2010–2024 and correlated antibody cutoffs to titres from a live-virus neutralisation test.

Individuals born before 1970 (n = 15,007) had antibody levels > 3,000 IU/L, persisting into higher age, and < 2% (n = 300) of them were seronegative. In contrast, individuals born after 1990 (n = 12,778) displayed seronegativity rates of 13–20% and lower median antibody concentrations in seropositive individuals (449–773 IU/L). In these individuals, antibody levels decreased noticeably between the ages of 2 and 10 years but remained stable between those aged 10 and 30 years. There was no significant difference in seronegativity rates at the age of 12–24 months in children born 2016–2019 and 2020–2022 (the years of the COVID-19 pandemic).

In Austria, there are significant immunity gaps in individuals born after 1970, which pre-existed before the COVID-19 pandemic. Thus, young and middle-aged populations not immune against measles should be vaccinated to counteract a further decline of immunity at the population level and prevent outbreaks whenever MeV is imported.

Respiratory syncytial virus (RSV) is a leading cause of hospitalisation in children worldwide. Recent regulatory approval of monoclonal antibody (mAb) nirsevimab for infants and the RSVpreF vaccine for pregnant women offers promising approaches to mitigate RSV-associated morbidity.

To evaluate potential impacts of routine prophylactic campaigns (mAbs targeting infants or maternal vaccination) introduced in the 2024/25 season on hospitalisations from RSV lower respiratory tract infections in Lombardy, Italy.

We used a catalytic model informed by data from pre-COVID-19 pandemic (before 2020) and post-pandemic periods (until 2022) to quantify the number of cases and hospitalisations that could be averted by seasonal nirsevimab administration to infants and RSVpreF maternal vaccination, considering changes in susceptibility caused by reduced RSV circulation during the pandemic.

As a marked proportion of RSV hospitalisations occurs in infants aged ≤ 1 year, seasonal mAb administration to 80% of newborns (uptake levels observed in Spain) was estimated to avert 50.2% (95% CI: 43.5–55.8) of hospitalisations in the total population. Coverage levels close to those observed for childhood vaccines (95%) could result in an additional average 18% reduction in hospitalisations. Vaccination of 65% of pregnant women, resembling the diphtheria–tetanus–pertussis vaccine coverage in Lombardy for this population, was estimated to avert 30.5% (95% CI: 19.6–39.7) of hospitalisations. At influenza vaccine coverage (12%), less than 8% of hospitalisations could be averted by maternal immunisation.

Routine nirsevimab administration to infants demonstrates clear potential to reduce RSV-associated hospitalisations. Maternal immunisation can help in achieving high protection in at-risk populations.

During the first year of the COVID-19 pandemic, vaccination programmes targeted children and adolescents to prevent severe outcomes of SARS-CoV-2 infection.

To estimate COVID-19 vaccine effectiveness (VE) against hospitalisation due to COVID-19 in the paediatric population, among those with and without previously documented SARS-CoV-2 infection.

We established a fixed cohort followed for 12 months in Denmark, Norway, Italy, Luxembourg, Navarre (Spain) and Portugal using routine electronic health registries. The study commenced with paediatric COVID-19 vaccination campaign at each site between June 2021 and January 2022. The outcome was hospitalisation with a laboratory-confirmed SARS-CoV-2 infection or COVID-19 as the main diagnosis. Using Cox proportional hazard models, VE was estimated as 1 minus the confounder-adjusted hazard ratio of COVID-19 hospitalisation between vaccinated and unvaccinated. A random-effects meta-analysis was used to pool VE estimates.

We included 4,144,667 5–11-year-olds and 3,861,841 12–17-year-olds. In 12–17-year-olds without previous infection, overall VE was 69% (95% CI: 40 to 84). VE declined with time since vaccination from 77% ≤ 3 months to 48% 180–365 days after immunisation. VE was 94% (95% CI: 90 to 96), 56% (95% CI: 3 to 80) and 41% (95% CI: −14 to 69) in the Delta, Omicron BA.1/BA.2 and BA.4/BA.5 periods, respectively. In 12–17-year-olds with previous infection, one dose VE was 80% (95% CI: 18 to 95). VE estimates were similar for 5–11-year-olds but with lower precision.

Vaccines recommended for 5–17-year-olds provided protection against COVID-19 hospitalisation, regardless of a previously documented infection of SARS-CoV-2, with high levels of protection in the first 3 months of the vaccination.