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- COVID-19 Vaccine Effectiveness Against Medically Attended Symptomatic SARS-CoV-2 Infection Among Target Groups in Europe, October 2024-January 2025, VEBIS Primary Care NetworkPublication . Delaunay, Charlotte Laniece; Verdasca, Nuno; Monge, Susana; Domegan, Lisa; Sève, Noémie; Buda, Silke; Meijer, Adam; Lucaccioni, Héloïse; Torrijos, Miriam López; McKenna, Adele; Enouf, Vincent; Dürrwald, Ralf; In't Velt, Eline; Laiglesia, Mª Ángel de Valcárcel; Bennett, Charlene; Masse, Shirley; Erdwiens, Annika; Hooiveld, Mariette; Mlinarić, Ivan; Túri, Gergő; Rodrigues, Ana Paula; Martínez-Baz, Iván; Lazar, Mihaela; Latorre-Margalef, Neus; Borges, Vitor; Kaczmarek, Marlena; Bacci, Sabrina; Kissling, Esther; European primary care VE groupWe estimated the effectiveness of 2024/25 COVID-19 vaccination against medically attended SARS-CoV-2 infection in Europe, among target groups. We included 3204 patients (8/139 cases vaccinated: 6%; 517/3065 controls vaccinated: 17%) from a multicentre, test-negative design study at primary care level. Vaccine effectiveness was 66% (95% CI: 34-85) overall, 73% (95% CI: 21-94) and 54% (95% CI: -3 to 83) in the first and second months post-vaccination, respectively. Overall vaccine effectiveness was 67% (95% CI: 33-86) among older adults (≥ 60 or ≥ 65 years). This relatively high COVID-19 VE (compared with previous seasons), as well as trends by time since vaccination, should be confirmed with additional data, as sample size was low.
- COVID-19 Vaccine Effectiveness in Autumn and Winter 2022 to 2023 Among Older EuropeansPublication . Laniece Delaunay, Charlotte; Mazagatos, Clara; Martínez-Baz, Iván; Túri, Gergő; Goerlitz, Luise; Domegan, Lisa; Meijer, Adam; Rodrigues, Ana Paula; Sève, Noémie; Ilić, Maja; Latorre-Margalef, Neus; Lazar, Mihaela; Maurel, Marine; Melo, Aryse; Andreu Ivorra, Blanca; Casado, Itziar; Horváth, Judit Krisztina; Buda, Silke; Bennett, Charlene; de Lange, Marit; Guiomar, Raquel; Enouf, Vincent; Mlinarić, Ivan; Samuelsson Hagey, Tove; Dinu, Sorin; Rumayor, Mercedes; Castilla, Jesús; Oroszi, Beatrix; Dürrwald, Ralf; O’Donnell, Joan; Hooiveld, Mariëtte; Gómez, Verónica; Falchi, Alessandra; Kurečić Filipović, Sanja; Dillner, Lena; Popescu, Rodica; Bacci, Sabrina; Kaczmarek, Marlena; Kissling, Esther; Gallardo García, Virtudes; Perez Morilla, Esteban; Pedrosa Corral, Irene; García Vázquez, Miriam; Milagro-Beamonte, Ana; Fernandez Ibañez, Ana; Margolles Martins, Mario; Giménez Duran, Jaume; Sastre Palou, Bartolomé; López Causapé, Carla; Viloria Raymundo, Luis Javier; Vega Alonso, Tomás; Ordax Díez, Ana; Lozano Alonso, Jose Eugenio; Rojo Bello, Silvia; Mendioroz, Jacobo; Basile, Luca; Martínez Mateo, Ana Isabel; Ruiz de Porras, Carlota; Moya Garcés, Alba; Marcos, Mª Ángeles; López Maside, Aurora; Botella Quijal, Francesc; Miralles Espi, Maite; Andreu Salete, Cristina; García Rodríguez, María del Carmen; Linares, Juan Antonio; García Comas, Luis; Barranco, Mª Isabel; Chirlaque, María-Dolores; Moreno Docón, Antonio; Ramos Marín, Violeta; Castrillejo, Daniel; Gómez Anés, Atanasio; Larrauro, Amparo; Pérez-Gimeno, Gloria; Lozano Álvarez, Marcos; Vega, Lorena; Galindo, Silvia; Puma, Tania; Monge, Susana; Pozo, Francisco; Casas, Inmaculada; Sandonis, Virginia; Vázquez-Morón, Sonia; Echeverría, Aitziber; Trobajo-Sanmartín, Camino; García Cenoz, Manuel; Ezpeleta, Guillermo; Ezpeleta, Carmen; Navascués, Ana; Krisztalovics, Katalin; Mucsányiné Juhász, Krisztina; Kristóf, Katalin; Preuss, Ute; Wedde, Marianne; Biere, Barbara; Reiche, Janine; Oh, Djin-Ye; McKenna, Adele; Connell, Jeff; Joyce, Michael; Bagheri, Mariam; Bos, Sanne; van den Brink, Sharon; Dijkstra, Frederika; Eggink, Dirk; van Gageldonk-Lafeber, Rianne; Goderski, Gabriel; Herrebrugh, Chantal; Jenniskens, Liz; Reukers, Daphne; Sluimer, John; Sprong, Tara; Teirlinck, Anne; Veldhijzen, Nienke; van der Burgh, Ruben; Kager, Cathrien; Klinkhamer, Mayra; Knottnerus, Bart; Riethof, Marloes; van den Broek, Ruud; Wortel, Safira; Machado, Ausenda; Kislaya, Irina; Aniceto, Carlos; Gomes, Licínia; Verdasca, Nuno; Henriques, Camila; Dias, Daniela; Lança, Miguel; Blanchon, Thierry; Guerrisi, Caroline; Renard, Aubane; Launay, Titouan; Masse, Shirley; Chazelle, Marie; Ferenčak, Ivana; Kaić, Bernard; Višekruna Vučina, Vesna; Čusek Adamić, Katica; Kosanović Ličina, Mirjana Lana; Lakošeljac, Danijela; Mihin Huskić, Ivana; Nonković, Diana; Carnahan, Annasara; Hansson-Pihlainen, Eva; Arvesen, Elin; Nid, Nora; Hansen, Anna-Lena; Andersson, Emmi; Dillner, Lena; Jidovu, Adrian; Timnea, Olivia Carmen; Pascu, Cătălina; Oprea, Mihaela; Bistriceanu, Iulia; Ivanciuc, Alina; Mihai, Maria Elena; VEBIS Primary Care Vaccine Effectiveness GroupKey Points: - Question: What was the effectiveness of COVID-19 vaccines administered in autumn and winter 2022 to 2023 against symptomatic SARS-CoV-2 infection among people aged 60 years or older in Europe, and how did different exposed or reference groups affect effectiveness? - Findings: In this case-control study of 9308 primary care patients at 11 European sites, within 3 months of vaccination, all COVID-19 vaccine effectiveness (CVE) estimates were 29% to 39% against SARS-CoV-2 viruses and 44% to 52% against the XBB variants. All point estimates decreased by time after vaccination, with no vaccine protection after 6 months. - Meaning: Findings of this study suggest that COVID-19 vaccination campaigns should precede peaks in SARS-CoV-2 incidence and that effectiveness of new vaccines against emerging variants should be continually monitored using seasonal CVE approaches.
- Effectiveness of complete primary vaccination against COVID-19 at primary care and community level during predominant Delta circulation in Europe: multicentre analysis, I-MOVE-COVID-19 and ECDC networks, July to August 2021Publication . Kissling, Esther; Hooiveld, Mariëtte; Martínez-Baz, Iván; Mazagatos, Clara; William, Naoma; Vilcu, Ana-Maria; Kooijman, Marjolein N.; Ilić, Maja; Domegan, Lisa; Machado, Ausenda; de Lusignan, Simon; Lazar, Mihaela; Meijer, Adam; Brytting, Mia; Casado, Itziar; Larrauri, Amparo; Murray, Josephine-L.K.; Behillil, Sylvie; de Gier, Brechje; Mlinarić, Ivan; O’Donnell, Joan; Rodrigues, Ana Paula; Tsang, Ruby; Timnea, Olivia; de Lange, Marit; Riess, Maximilian; Castilla, Jesús; Pozo, Francisco; Hamilton, Mark; Falchi, Alessandra; Knol, Mirjam J.; Kurečić Filipović, Sanja; Dunford, Linda; Guiomar, Raquel; Cogdale, Jade; Cherciu, Carmen; Jansen, Tessa; Enkirch, Theresa; Basile, Luca; Connell, Jeff; Gómez, Verónica; Sandonis Martín, Virginia; Bacci, Sabrina; Rose, Angela M.C.; Pastore Celentano, Lucia; Valenciano, Marta; I-MOVE-COVID-19 and ECDC primary care study teamsIntroduction: In July and August 2021, the SARS-CoV-2 Delta variant dominated in Europe. Aim: Using a multicentre test-negative study, we measured COVID-19 vaccine effectiveness (VE) against symptomatic infection. Methods: Individuals with COVID-19 or acute respiratory symptoms at primary care/community level in 10 European countries were tested for SARS-CoV-2. We measured complete primary course overall VE by vaccine brand and by time since vaccination. Results: Overall VE was 74% (95% CI: 69–79), 76% (95% CI: 71–80), 63% (95% CI: 48–75) and 63% (95% CI: 16–83) among those aged 30–44, 45–59, 60–74 and ≥ 75 years, respectively. VE among those aged 30–59 years was 78% (95% CI: 75–81), 66% (95% CI: 58–73), 91% (95% CI: 87–94) and 52% (95% CI: 40–61), for Comirnaty, Vaxzevria, Spikevax and COVID-19 Vaccine Janssen, respectively. VE among people 60 years and older was 67% (95% CI: 52–77), 65% (95% CI: 48–76) and 83% (95% CI: 64–92) for Comirnaty, Vaxzevria and Spikevax, respectively. Comirnaty VE among those aged 30–59 years was 87% (95% CI: 83–89) at 14–29 days and 65% (95% CI: 56–71%) at ≥ 90 days between vaccination and onset of symptoms. Conclusions: VE against symptomatic infection with the SARS-CoV-2 Delta variant varied among brands, ranging from 52% to 91%. While some waning of the vaccine effect may be present (sample size limited this analysis to only Comirnaty), protection was 65% at 90 days or more between vaccination and onset.
- Effectiveness of COVID-19 vaccines administered in the 2023 autumnal campaigns in Europe: Results from the VEBIS primary care test-negative design study, September 2023–January 2024Publication . Laniece Delaunay, Charlotte; Melo, Aryse; Maurel, Marine; Mazagatos, Clara; Goerlitz, Luise; O’Donnell, Joan; Oroszi, Beatrix; Sève, Noémie; Rodrigues, Ana Paula; Martínez-Baz, Iván; Meijer, Adam; Mlinarić, Ivan; Latorre-Margalef, Neus; Lazăr, Mihaela; Pérez-Gimeno, Gloria; Dürrwald, Ralf; Bennett, Charlene; Túri, Gergő; Rameix-Welti, Marie-Anne; Guiomar, Raquel; Castilla, Jesús; Hooiveld, Mariëtte; Kurečić Filipović, Sanja; Samuelsson Hagey, Tove; Dijkstra, Frederika; Borges, Vitor; Ramos Marín, Violeta; Bacci, Sabrina; Kaczmarek, Marlena; Kissling, Esther; European primary care VE groupIn autumn 2023, European vaccination campaigns predominantly administered XBB.1.5 vaccine. In a European multicentre study, we estimated 2023 COVID-19 vaccine effectiveness (VE) against laboratory-confirmed symptomatic infection at primary care level between September 2023 and January 2024. Using a testnegative case–control design, we estimated VE in the target group for COVID-19 vaccination overall and by time since vaccination. We included 1057 cases and 4397 controls. Vaccine effectiveness was 40 % (95 % CI: 26–53 %) overall, 48 % (95 % CI: 31–61 %) among those vaccinated < 6 weeks of onset and 29 % (95 % CI: 3–49 %) at 6–14 weeks. Our results suggest that COVID-19 vaccines administered to target groups during the autumn 2023 campaigns showed clinically significant effectiveness against laboratory-confirmed, medically attended symptomatic SARS-CoV-2 infection in the 3 months following vaccination. A longer study period will allow for further variant-specific COVID-19 VE estimates, better understanding decline in VE and informing booster administration policies.
- Effectiveness of XBB.1.5 Vaccines Against Symptomatic SARS‐CoV‐2 Infection in Older Adults During the JN.1 Lineage‐Predominant Period, European VEBIS Primary Care Multicentre Study, 20 November 2023–1 March 2024Publication . Merdrignac, Lore; Laniece Delaunay, Charlotte; Verdasca, Nuno; Vega‐Piris, Lorena; O'Donnell, Joan; Sève, Noémie; Trobajo‐Sanmartín, Camino; Buda, Silke; Hooiveld, Mariëtte; Rodrigues, Ana Paula; Túri, Gergő; Latorre‐Margalef, Neus; Mlinarić, Ivan; Lazar, Mihaela; Maurel, Marine; Castrillejo, Daniel; Bennett, Charlene; Rameix‐Welti, Marie‐Anne; Martínez‐Baz, Iván; Dürrwald, Ralf; Meijer, Adam; Melo, Aryse; Oroszi, Beatrix; Hagey, Tove Samuelsson; Kurečić Filipović, Sanja; Dijkstra, Frederika; Gómez, Verónica; Bacci, Sabrina; Kaczmarek, Marlena; Kissling, Esther; VEBIS Primary Care Vaccine Effectiveness GroupWe estimated XBB.1.5 vaccine effectiveness (VE) against symptomatic SARS-CoV-2 infection among adults aged ≥65 years during the 2023/2024 JN.1 lineage-predominant period in a European multi-country test-negative case–control study at primary care level. We estimated VE adjusted by study site, age, sex, chronic conditions and onset date. We included 220 cases and 1733 controls. The VE was 48% (95% CI: 12–71), 23% (95% CI: −11–48) and 5% (95% CI: −92–56) among those with symptom onset 1–5, 6–11, and ≥12weeks after vaccination, respectively. XBB.1.5 vaccine provided short and moderate protection against JN.1 symptomatic infection.
- Exploring the effect of clinical case definitions on influenza vaccine effectiveness estimation at primary care level: Results from the end-of-season 2022–23 VEBIS multicentre study in EuropePublication . Maurel, Marine; Mazagatos, Clara; Goerlitz, Luise; Oroszi, Beatrix; Hooiveld, Mariette; Machado, Ausenda; Domegan, Lisa; Ilić, Maja; Popescu, Rodica; Sève, Noémie; Martínez-Baz, Iván; Larrauri, Amparo; Buda, Silke; Túri, Gergő; Meijer, Adam; Gómez, Verónica; O'Donnell, Joan; Mlinarić, Ivan; Timnea, Olivia; Diez, Ana Ordax; Dürrwald, Ralf; Horváth, Judit Krisztina; Dijkstra, Frederika; Rodrigues, Ana Paula; McKenna, Adele; Filipović, Sanja Kurečić; Lazar, Mihaela; Kaczmarek, Marlena; Bacci, Sabrina; Kissling, Esther; VEBIS study teamBackground: Within influenza vaccine effectiveness (VE) studies at primary care level with a laboratory-confirmed outcome, clinical case definitions for recruitment of patients can vary. We used the 2022-23 VEBIS primary care European multicentre study end-of-season data to evaluate whether the clinical case definition affected IVE estimates. Methods: We estimated VE using a multicentre test-negative case-control design. We measured VE against any influenza and influenza (sub)types, by age group (0-14, 15-64, ≥65 years) and by influenza vaccine target group, using logistic regression. We estimated IVE among patients meeting the European Union (EU) acute respiratory infection (ARI) case definition and among those meeting the EU influenza-like illness (ILI) case definition, including only sites providing information on specific symptoms and recruiting patients using an ARI case definition (as the EU ILI case definition is a subset of the EU ARI one). Results: We included 24 319 patients meeting the EU ARI case definition, of whom 21 804 patients (90 %) meet the EU ILI case definition, for the overall pooled VE analysis against any influenza. The overall and influenza (sub)type-specific VE varied by ≤2 % between EU ILI and EU ARI populations. Discussion: Among all analyses, we found similar VE estimates between the EU ILI and EU ARI populations, with few (10%) additional non-ILI ARI patients recruited. These results indicate that VE in the 2022-23 influenza season was not affected by use of a different clinical case definition for recruitment, although we recommend investigating whether this holds true for next seasons.
- Influenza vaccine effectiveness in Europe and the birth cohort effect against influenza A(H1N1)pdm09: VEBIS primary care multicentre study, 2023/24Publication . Kissling, Esther; Maurel, Marine; Pozo, Francisco; Pérez-Gimeno, Gloria; Buda, Silke; Sève, Noémie; Domegan, Lisa; Hooiveld, Mariëtte; Oroszi, Beatrix; Martínez-Baz, Iván; Guiomar, Raquel; Latorre-Margalef, Neus; Mlinarić, Ivan; Lazar, Mihaela; Giménez Duran, Jaume; Dürrwald, Ralf; Enouf, Vincent; McKenna, Adele; de Lange, Marit; Túri, Gergő; Trobajo-Sanmartín, Camino; GOMEZ TEIXEIRA PINTO, VERÓNICA DEL PILAR; Samuelsson Hagey, Tove; Višekruna Vučina, Vesna; Cherciu, Maria Carmen; García Vazquez, Miriam; Erdwiens, Annika; Masse, Shirley; Bennett, Charlene; Meijer, Adam; Kristóf, Katalin; Castilla, Jesús; Rodrigues, Ana Paula; Kurečić Filipović, Sanja; Ivanciuc, Alina Elena; Bacci, Sabrina; Kaczmarek, MarlenaIntroduction: 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. Aim: The VEBIS primary care network estimated influenza VE in Europe using a multicentre test-negative study. Methods: 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. Results: 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. Discussion: 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.
- Influenza vaccine effectiveness in Europe: Results from the 2022–2023 VEBIS (Vaccine Effectiveness, Burden and Impact Studies) primary care multicentre studyPublication . Maurel, Marine; Pozo, Francisco; Pérez‐Gimeno, Gloria; Buda, Silke; Sève, Noémie; Oroszi, Beatrix; Hooiveld, Mariette; Gómez, Verónica; Domegan, Lisa; Martínez‐Baz, Iván; Ilić, Maja; Carnahan, Anna Sara; Mihai, Maria Elena; Martínez, Ana; Goerlitz, Luise; Enouf, Vincent; Horváth, Judit Krisztina; Dijkstra, Frederika; Rodrigues, Ana Paula; Bennett, Charlene; Trobajo‐Sanmartín, Camino; Mlinarić, Ivan; Latorre‐Margalef, Neus; Ivanciuc, Alina; Lopez, Aurora; Dürrwald, Ralf; Falchi, Alessandra; Túri, Gergő; Meijer, Adam; Melo, Aryse; O'Donnell, Joan; Castilla, Jesús; Vučina, Vesna Višekruna; Hagey, Tove Samuelsson; Lazar, Mihaela; Kaczmarek, Marlena; Bacci, Sabrina; Kissling, Esther; VEBIS Study TeamBackground: Influenza A(H3N2) viruses dominated early in the 2022-2023 influenza season in Europe, followed by higher circulation of influenza A(H1N1)pdm09 and B viruses. The VEBIS primary care network estimated the influenza vaccine effectiveness (VE) using a multicentre test-negative study. Materials and methods: Primary care practitioners collected information and specimens from patients consulting with acute respiratory infection. We measured VE against any influenza, influenza (sub)type and clade, by age group, by influenza vaccine target group and by time since vaccination, using logistic regression. Results: We included 38 058 patients, of which 3786 were influenza A(H3N2), 1548 influenza A(H1N1)pdm09 and 3275 influenza B cases. Against influenza A(H3N2), VE was 36% (95% CI: 25-45) among all ages and ranged between 30% and 52% by age group and target group. VE against influenza A(H3N2) clade 2b was 38% (95% CI: 25-49). Overall, VE against influenza A(H1N1)pdm09 was 46% (95% CI: 35-56) and ranged between 29% and 59% by age group and target group. VE against influenza A(H1N1)pdm09 clade 5a.2a was 56% (95% CI: 46-65) and 79% (95% CI: 64-88) against clade 5a.2a.1. VE against influenza B was 76% (95% CI: 70-81); overall, 84%, 72% and 71% were among 0-14-year-olds, 15-64-year-olds and those in the influenza vaccination target group, respectively. VE against influenza B with a position 197 mutation of the hemagglutinin (HA) gene was 79% (95% CI: 73-85) and 90% (95% CI: 85-94) without this mutation. Conclusion: The 2022-2023 end-of-season results from the VEBIS network at primary care level showed high VE among children and against influenza B, with lower VE against influenza A(H1N1)pdm09 and A(H3N2).
- Interim 2023/24 influenza A vaccine effectiveness: VEBIS European primary care and hospital multicentre studies, September 2023 to January 2024Publication . Maurel, Marine; Howard, Jennifer; Kissling, Esther; Pozo, Francisco; Pérez-Gimeno, Gloria; Buda, Silke; Sève, Noémie; McKenna, Adele; Meijer, Adam; Rodrigues, Ana Paula; Martínez-Baz, Iván; Mlinarić, Ivan; Latorre-Margalef, Neus; Túri, Gergő; Lazăr, Mihaela; Mazagatos, Clara; Echeverria, Aitziber; Abela, Stephen; Bourgeois, Marc; Machado, Ausenda; Dürrwald, Ralf; Petrović, Goranka; Oroszi, Beatrix; Jancoriene, Ligita; Marin, Alexandru; Husa, Petr; Duffy, Roisin; Dijkstra, Frederika; Gallardo García, Virtudes; Goerlitz, Luise; Enouf, Vincent; Bennett, Charlene; Hooiveld, Mariëtte; Guiomar, Raquel; Trobajo-Sanmartín, Camino; Višekruna Vučina, Vesna; Samuelsson Hagey, Tove; Lameiras Azevedo, Ana Sofía; Castilla, Jesús; Xuereb, Gerd; Delaere, Bénédicte; Gómez, Verónica; Tolksdorf, Kristin; Bacci, Sabrina; Nicolay, Nathalie; Kaczmarek, Marlena; Rose, Angela MC; European IVE groupInfluenza A viruses circulated in Europe from September 2023 to January 2024, with influenza A(H1N1)pdm09 predominance. We provide interim 2023/24 influenza vaccine effectiveness (IVE) estimates from two European studies, covering 10 countries across primary care (EU-PC) and hospital (EU-H) settings. Interim IVE was higher against A(H1N1)pdm09 than A(H3N2): EU-PC influenza A(H1N1)pdm09 IVE was 53% (95% CI: 41 to 63) and 30% (95% CI: −3 to 54) against influenza A(H3N2). For EU-H, these were 44% (95% CI: 30 to 55) and 14% (95% CI: −32 to 43), respectively.
- Recommendations for estimating and reporting vaccine effectiveness by time since vaccination: a COVID-19 case studyPublication . Kissling, Esther; Nunes, Baltazar; Hooiveld, Mariëtte; Martínez-Baz, Iván; Monge, Susana; Robertson, Chris; Knolm, Mirjam; Sève, Noémie; Mlinarić, Ivan; Domegan, Lisa; Machado, Ausenda; Whitaker, Heather; Lazar, Mihaela; Meijer, Adam; Enkirch, Theresa; Casado, Itziar; Pérez-Gimeno, Gloria; William, Naoma; Enouf, Vincent; Kurečić Filipović, Sanja; McKenna, Adele; Rodrigues, Ana Paula; de Lusignan, Simon; Timnea, Olivia-Carmen; Latorre-Margalef, Neus; Castilla, Jesús; Pozo, Francisco; Hamilton, Mark; Masse, Shirley; Ilić, Maja; Basile, Luca; O’Donnell, Joan; Guiomar, Raquel; Riess, Maximilian; Popescu, Rodica-Manuela; M C Rose, Angela; Andrews, Nick; Bacci, Sabrina; Pastore Celentano, Lucia; Valenciano, Marta; Moren, Alain; Beutels, Philippe; Hens, Niel; I-MOVE-COVID-19 and ECDC primary care study teamsEstimating COVID-19 vaccine effectiveness (VE) by time since vaccination (TSV) is essential for understanding how protection may change over time and enables meaningful comparisons across studies. This is important for accurate comparisons of VE against different SARS-CoV-2 variants/sublineages, across age groups, during different periods post vaccination campaign, or by vaccine type/brand. We provide recommendations for case–control VE studies on estimating and reporting VE analyses by TSV, with the aim of improving quality of these estimates. Our recommendations cover study design and pre-analysis considerations, descriptive analyses, choice of categories of TSV, categorical and continuous modelling approaches, and best practices for reporting VE by TSV. Using a real-life case–control study, we apply these recommendations, and include accompanying statistical scripts in R and Stata. These recommendations will serve as a practical resource for researchers conducting VE analyses by TSV. We encourage ongoing refinement of them through input from other study groups.
