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- COVID-19 vaccination and antibody response in healthcare workers: a longitudinal serological study following the 2023-2024 COVID-19 vaccination campaignPublication . Almeida Santos, João; Henriques, Camila; Amaral, Palmira; Guiomar, Raquel; Machado, Ausenda; Gaio, VâniaBackground: Healthcare workers (HCWs) are essential frontline responders to public health emergencies and are one of the risk groups targeted by annual vaccination campaigns. Serological studies are valuable for high-risk groups such as HCWs, as they contribute to assess vulnerability, monitor infection control measures, and guide vaccination strategies in high-risk settings. This study aimed to assess humoral response at baseline, 3 and 6 months after the 2023–2024 COVID-19 vaccination campaign in HCWs, and to identify demographic and clinical factors associated with variations in antibody levels over time. Methods: Prospective cohort study of vaccinated HCWs at a central hospital in Portugal (September 2023–May 2024). Serial serological tests to assess anti-spike receptor-binding domain (anti-RBD/S) and anti-nucleocapsid protein (anti-N) IgG antibodies were used to monitor the immune response and SARS-CoV-2 infection history, respectively. Wilcoxon signed-rank tests were used to assess changes in antibody levels over time, and linear regression models were used to identify factors associated with variations in SARS-CoV-2 anti-RBD/S IgG concentrations, on the basis of available demographic and clinical data. Results: In a cohort of 166 HCWs who received the 2023–2024 COVID-19 booster vaccine, anti-RBD/S IgG antibody levels significantly increased at 3 months post-vaccination (16 007.4 vs. 30 572.9 AU/mL) before declining by 6 months (18 327.3 AU/mL), nearing baseline levels. Previous infection (β = 1.92, 95% CI: 1.33-2.77) and older age (β = 2.65, 95%CI: 1.64‐4.29) were associated with higher antibody concentrations at baseline, whereas smoking was linked to lower antibody levels at 6 months (β = 0.32, 95%CI: 0.11–0.88). Other factors, such as sex and chronic conditions, had no consistent significant impact over time. Conclusions: Although SARS-CoV-2 anti-RBD/S IgG antibody concentrations declined significantly six months after the 2023–2024 COVID-19 booster vaccination, they remained at relatively high concentrations over the follow-up period. This study provides new insight into these dynamics in a highly vaccinated and exposed HCWs cohort during a later post-pandemic phase, highlighting the influence of prior infection, age, and smoking on antibody persistence and reinforces the relevance of ongoing immune monitoring of this risk group to guide tailored control strategies. However, vaccine effectiveness studies in highly exposed and vaccinated populations, such as HCWs, are needed to better inform the role of antibody monitoring in this context, especially given the ongoing trend of annually updated vaccines.
- COVID-19 Vaccine Effectiveness Against Hospitalization in Older Adults, VEBIS Hospital Network, Europe, September 2024-May 2025Publication . Rojas-Castro, Madelyn; Verdasca, Nuno; Monge, Susana; De Mot, Laurane; Trobajo-Sanmartín, Camino; Duffy, Róisín; Túri, Gergő; Kuliese, Monika; Duerrwald, Ralf; Borg, Maria-Louise; Popovici, Odette; Gomez, Verónica; Makarić, Zvjezdana Lovrić; Launay, Odile; Marques, Diogo F.P.; Pozo, Francisco; Witdouck, Arne; Martínez-Baz, Iván; Fitzgerald, Margaret; Oroszi, Beatrix; Jančorienė, Ligita; Buda, Silke; Dziugyte, Ausra; Lazăr, Mihaela; Machado, Ausenda; Tabain, Irena; Nguyen, Liem Binh Luong; Wagner, Eva Rivas; Dufrasne, François; Castilla, Jesús; Domegan, Lisa; Velkey, Viktória; Majauskaite, Fausta; Hackmann, Carolin; Nicolay, Nathalie; Bacci, Sabrina; Rose, Angela M.C.; European Hospital Vaccine Effectiveness GroupWe estimated COVID-19 vaccine effectiveness (VE) against PCR-confirmed SARS-CoV-2 hospitalization in patients ≥ 60 years with severe acute respiratory infection, using a multicenter, test-negative, case-control study across seven sites in six European countries between September 2024 and May 2025. We included 352 cases (115 vaccinated; 33%) and 9980 controls (5024 vaccinated; 50%). VE was 42% (95% CI: 15; 61) 14-59 days post-vaccination, 32% (95% CI: -1; 54) at 60-119 days, and 36% (95% CI: 2; 60) at 120-179 days, and no effect thereafter. Among adults aged 60-79 and ≥ 80 years, we observed moderate VE against COVID-19 hospitalization for up to 2 and 4 months, respectively.
- COVID-19 Vaccine Effectiveness among older adultsPublication . Laniece Delaunay, Charlotte; Mateo-Urdiales, Alberto; Pérez-Gimeno, Gloria; O'Reilly, Karen; Uras, Marina; Erdwiens, Annika; Mlinaric, Ivan; Túri, Gergo; Martínez-Baz, Iván; Meijer, Adam; Rodrigues, Ana Paula; Lazar, Mihaela; Latorre-Margalef, Neus; Lucaccioni, Héloïse; Verdasca, Nuno; Bella, Antonino; Rafael de la Cruz Lopez, Maria Angeles; Kelly, Eva; Enouf, Vincent; Tolksdorf, Kristin; Puzelli, Simona; Ibáñez Pérez, Ana Carmen; Fitzgerald, Margaret; Masse, Shirley; Oh, Djin-Ye; Kaczmarek, Marlena; Bacci, Sabrina; Kissling, Esther; VEBIS Primary Care Vaccine Effectiveness GroupIntroduction: From September to November 2025, many European countries launched COVID-19 vaccination campaigns, when SARS-CoV-2 incidence was decreasing after a period of high circulation.1 These campaigns targeted specific groups, including older adults (ie, individuals aged at or above a minimum threshold that varied from age 60 to 70 years across countries). We estimated the effectiveness of COVID-19 vaccines administered during these seasonal vaccination campaigns in Europe against medically attended, symptomatic SARS-CoV-2 infection among older adults, from September 29, 2025, to January 10, 2026.
- COVID-19 vaccine effectiveness in the paediatric population aged 5-17 years: a multicentre cohort study using electronic health registries in six European countries, 2021 to 2022Publication . Soares, Patricia; Machado, Ausenda; Nicolay, Nathalie; Monge, Susana; Sacco, Chiara; Hansen, Christian Holm; Meijerink, Hinta; Martínez-Baz, Iván; Schmitz, Susanne; Humphreys, James; Fabiani, Massimo; Echeverria, Aitziber; AlKerwi, Ala'a; Nardone, Anthony; Mateo-Urdiales, Alberto; Castilla, Jesús; Kissling, Esther; Nunes, Baltazar; VEBIS-Lot 4 working groupBackground: During the first year of the COVID-19 pandemic, vaccination programmes targeted children and adolescents to prevent severe outcomes of SARS-CoV-2 infection. Aim: 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. Methods: 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. Results: 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. Conclusion: 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.
- Do COVID-19 and Influenza vaccines influence susceptibility to other respiratory viruses? A population based studyPublication . Almeida Santos, João; Gomez, Verónica; Guiomar, Raquel; Verdasca, Nuno; Gomes, Licínia; Machado, Ausenda; Rodrigues, Ana PaulaIntroduction: Studies have raised concerns that Influenza and COVID-19 vaccination may influence susceptibility to other respiratory viruses (ORV), potentially increasing the risk of non-target infections. This challenges a key assumption of test-negative design studies—that vaccines do not affect the risk of other infections within the same clinical syndrome. Nevertheless, current evidence remains inconclusive. This study aimed to evaluate the association between COVID-19 and influenza vaccination and the risk of non-influenza/COVID-19 respiratory virus infections. Methods: Test-negative design (TND) study using Portuguese data from a primary care vaccine effectiveness study (VEBIS Primary Care study) between October/2022-April/2025. Data on influenza/COVID-19 vaccination status, age, sex and chronic conditions were collected. Samples were tested by RT-PCR for influenza, SARS-CoV-2 and ORV. Patients with laboratory-confirmed influenza/COVID-19 infection were excluded. Logistic regression estimated adjusted odds ratios (aOR) of being vaccinated among cases (ORV positive) and controls (pan-negative). Results: Of the 1096 patients included, 4.5% received the COVID-19 vaccine, 5.9% the influenza vaccine, 13.3% both, and 76.3% neither. Human Rhinovirus (44.2%), human Coronavirus (14.6%) and Respiratory Syncytial Virus (14.1%) were the viruses more frequently identified. Individuals 65+ exhibited significant lower odds of infection with ORV (OR=0.45, 95%CI:0.25-0.81) compared to younger age group (<18yo). Vaccination status, including influenza only (aOR=1.01, 95%CI:0.59‐1.72), COVID only (aOR=0.88, 95%CI:0.48‐1.59), and both vaccines (aOR=1.38, 95%CI:0.92‐2.06), were not associated to ORV infection risk. Conclusions: Our results suggest that vaccination status—whether for influenza, COVID-19, or both—was not significantly associated with the risk of ORV infections. This supports the use of test-negative controls for influenza/COVID-19 within the same clinical syndrome, as it upholds a key TND assumption of no association between vaccination and risk of non-target infections. While mechanisms such as reduced cross-protection from natural infection or potential vaccine-induced cross-immunity have been proposed, our findings reinforce the validity of the primary methodological assumption rather than suggesting evidence for these alternative effects.
- Effectiveness of the XBB.1.5 COVID-19 Vaccines Against SARS-CoV-2 Hospitalisation Among Adults Aged ≥ 65 Years During the BA.2.86/JN.1 Predominant Period, VEBIS Hospital Study, Europe, November 2023 to May 2024Publication . Antunes, Liliana; Rojas-Castro, Madelyn; Lozano, Marcos; Martínez-Baz, Iván; Leroux-Roels, Isabel; Borg, Maria-Louise; Oroszi, Beatrix; Fitzgerald, Margaret; Dürrwald, Ralf; Jancoriene, Ligita; Machado, Ausenda; Petrović, Goranka; Lazar, Mihaela; Součková, Lenka; Bacci, Sabrina; Howard, Jennifer; Verdasca, Nuno; Basile, Luca; Castilla, Jesús; Ternest, Silke; Džiugytė, Aušra; Túri, Gergő; Duffy, Roisin; Hackmann, Carolin; Kuliese, Monika; Gomez, Verónica; Makarić, Zvjezdana Lovrić; Marin, Alexandru; Husa, Petr; Nicolay, Nathalie; Rose, Angela M.C.; VEBIS SARI VE network teamWe estimated the effectiveness of the adapted monovalent XBB.1.5 COVID-19 vaccines against PCR-confirmed SARS-CoV-2 hospitalisation during the BA.2.86/JN.1 lineage-predominant period using a multicentre test-negative case-control study in Europe. We included older adults (≥ 65 years) hospitalised with severe acute respiratory infection from November 2023 to May 2024. Vaccine effectiveness was 46% at 14-59 days and 34% at 60-119 days, with no effect thereafter. The XBB.1.5 COVID-19 vaccines conferred protection against BA.2.86 lineage hospitalisation in the first 4 months post-vaccination.
- Genomic Analysis of Antibiotic Resistance and Virulence Profiles in Escherichia coli Linked to Sternal Bursitis in Chickens: A One Health PerspectivePublication . Ribeiro, Jessica; Silva, Vanessa; Freitas, Catarina; Pinto, Pedro; Vieira-Pinto, Madalena; Batista, Rita; Nunes, Alexandra; Gomes, João Paulo; Pereira, José Eduardo; Igrejas, Gilberto; Barros, Lillian; Heleno, Sandrina A.; Reis, Filipa S.; Poeta, PatríciaAbstract: Sternal bursitis is an underexplored lesion in poultry, often overlooked in microbiological diagnostics. In this study, we characterized 36 Escherichia coli isolates recovered from sternal bursitis in broiler chickens, combining phenotypic antimicrobial susceptibility testing, PCRbased screening, and whole genome sequencing (WGS). The genetic analysis revealed a diverse population spanning 15 sequence types, including ST155, ST201, and ST58. Resistance to tetracycline and ciprofloxacin was common, and several isolates carried genes encoding β-lactamases, including blaTEM-1B. Chromosomal mutations associated with quinolone and fosfomycin resistance (e.g., gyrA p.S83L, glpT_E448K) were also identified. WGS revealed a high number of virulence-associated genes per isolate (58–96), notably those linked to adhesion (fim, ecp clusters), secretion systems (T6SS), and iron acquisition (ent, fep, fes), suggesting strong pathogenic potential. Many isolates harbored virulence markers typical of ExPEC/APEC, such as iss, ompT, and traT, even in the absence of multidrug resistance. Our findings suggest that E. coli from sternal bursitis may act as reservoirs of resistance and virulence traits relevant to animal and public health. This highlights the need for including such lesions in genomic surveillance programs and reinforces the importance of integrated One Health approaches.
- Genomic diversity of Enterobacteriaceae on food-processing surfaces: an overlooked non-clinical setting with public health implicationsPublication . Peixoto, Andreia; Nova, Lúcia; Mourão, Joana; Matos, Cátia; Santos, Susana; Rodrigues, João; Saraiva, Margarida; Correia, Cristina Belo; Batista, Rita; Peixe, Luísa; Novais, Carla; Antunes, PatríciaBacterial hazards on contaminated surfaces in food-processing environments pose significant food safety risks. Hygiene monitoring of surfaces in direct or indirect contact with food typically relies on a limited set of bacterial indicators, such as Enterobacteriaceae counts. However, their genomic diversity remains poorly characterised. The aim of this study was to provide a comprehensive genomic characterisation of Enterobacteriaceae recovered from food-contact surfaces after cleaning and disinfection with biocides in foodservice units. Diverse strains were identified, with some STs shared across samples and/or foodservices. - A diverse Enterobacteriaceae population persists on food-contact surfaces even after cleaning and disinfection with biocides, with evidence of cross-contamination. - These surfaces represent critical points of contact for strains that are genetically similar to those circulating in food, environment, and human clinical sources, including strains carrying clinically relevant AMR genes. - Further research is needed to understand the factors driving their persistence and dissemination in foodservice environments, aiming to enhance food safety risk management protocols and protect public health.
- Genomic evolution and re-emergence of a multidrug-resistant Clostridioides difficile RT027 clone with reduced vancomycin susceptibility driving a prolonged hospital outbreakPublication . Isidro, Joana; Dionísio, Filipa; Alves, Frederico; Almeida, Soraia; Santos, Cláudia; Santos, Manuel Mota; Reis, Ernestina; Oliveira, Júlio R.; Gomes, João Paulo; Oleastro, MónicaFollowing an extended period of declining prevalence of the epidemic Clostridioides difficile ribotype 027 (RT027) in Portugal, a genetically distinct, multidrug-resistant (MDR) RT027 strain with reduced susceptibility to vancomycin has emerged, causing a 15-month outbreak. This investigation provides epidemiological and genomic evidence for renewed circulation and evolutionary adaptation of this high-risk lineage. A comprehensive outbreak investigation was conducted in a tertiary-care hospital in northern Portugal between 2023 and 2025. Epidemiological and clinical data, antimicrobial exposures, and infection-control measures were analysed. Whole-genome sequencing (WGS) was performed to characterize the outbreak clone. Sixty-six RT027 C. difficile infection (CDI) cases were confirmed, with incidence peaking at 5.46 cases per 10,000 patient-bed days in April 2024. WGS revealed an unusual accumulation of AMR determinants conferring a broad MDR phenotype. Notably, all isolates harboured the VanR T115A substitution, a rare mutation previously linked to reduced vancomycin susceptibility, raising concerns regarding evolving antimicrobial tolerance within RT027. The close relatedness to 2016-2018 USA isolates suggests a recent emergence of this clone. Transmission was facilitated by structural constraints, limited isolation capacity and shared sanitary facilities. This prolonged outbreak documents the re-emergence and genomic evolution of a hypervirulent RT027 lineage, characterized by a concerning expansion of antimicrobial resistance and decreased vancomycin susceptibility and a high recurrence rate (25%). These findings highlight the ongoing adaptive potential of C. difficile under antimicrobial pressure and underscore the need for strengthened surveillance, genomic monitoring, and infection-prevention strategies to mitigate re-establishment of epidemic RT027 strains in Europe and beyond.
- Impact of a revised late HIV diagnosis definition on late HIV estimates in Europe: A multi-country pilot studyPublication . Kirwan, P.; Stengaard, A.; Brännström, J.; Van Beckhoven, D.; van Sighem, A.; Op de Coul, E.; Bartmeyer, B.; Koppe, U.; C. Martins, H.; Maly, M.; Wessman, M.; Tsiara, C.; Ferentinos, G.; Suligoi, B.; Grabar, S.; Sullivan, A.K.; Reyes, J.; Pharris, A.; Kuchukhidze, G.; Kirk, O.; Croxford, S.; Delpech, V.; Raben, D.; EuroTEST Steering CommitteePurpose: Late HIV diagnosis has been defined as a CD4 count <350 cells/mL or AIDS-defining event. With improvements in HIV tests and testing frequency, more people in Europe are diagnosed during the acute/seroconversion phase, when their CD4 count can be temporarily low. A revised consensus definition of late HIV diagnosis* enables better distinction between people diagnosed late and those diagnosed during the acute/seroconversion phase. We aimed to pilot this revised definition with European countries. Method: Pseudo-anonymised HIV diagnosis records for 2022-2023 were collected from nine countries. Records included markers of recent HIV acquisition from laboratory evidence (RITA, p24), testing history (negative HIV test within 12 months), or clinical evidence (e.g. seroconversion illness). We applied the revised definition to reclassify those with recently acquired HIV as ‘not-late’. Late diagnosis correction factors were calculated as: (number reclassified)/(number with CD4<350 or AIDS-defining event) and evaluated by demographic factor. Results: Availability of recent acquisition evidence varied by country and individual marker. Of 10,241 diagnoses with CD4 counts reported, 56% (5,696/10,241) had a CD4<350 or AIDS-defining event, i.e. were initially classified as late. Of these, 563 had evidence of recent HIV acquisition: 168 had laboratory evidence, 238 testing history evidence, and 260 clinical evidence (could have multiple). After reclassification the late diagnosis rate was reduced from 56% to 50%,with an overall correction factor of 10% (563/5,696), ranging between 3-25% across countries . The correction factor was higher for younger individuals compared to older, and for MSM compared to other transmission routes . Conclusions: Without reclassification, late HIV diagnosis rates are overestimated, by up to 25% in young MSM. This correction addresses a lack of progress in reducing the percentage of people diagnosed late. For countries to undertake this correction, improved collection of recent acquisition markers at clinic and national levels is needed.
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