Coronavirus disease (COVID-19) has caused considerable morbidity and mortality with more than 66 million cases and 1.2 million deaths reported in the World Health Organization European Region as at 5 September 2021. The highly transmissible Delta variant (Phylogenetic Assignment of Named Global Outbreak (Pango) lineage designation B.1.617.2 and the AY sublineages) of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) dominated over the Alpha variant (B.1.1.7) in Europe from July 2021 onwards and accounted for more than 99% of sequenced samples in weeks 35–36 in 2021. From mid-March 2021, four COVID-19 vaccines were authorised in the European Union by the European Medicines Agency: two mRNA vaccines (Comirnaty and Spikevax) and two adenoviral vector vaccines (Vaxzevria and COVID-19 Vaccine Janssen). Before the circulation of the Delta variant, randomised controlled trials indicated a high efficacy for these vaccines. Observational post-authorisation studies in Europe are therefore important to measure the effectiveness of the different COVID-19 vaccines against the currently circulating Delta variant.
Recent discussions around recommendations for booster doses, for various populations, highlight the need to measure vaccine effectiveness (VE) by time since vaccination. Many studies have reported a decrease in VE against infection with increasing time since vaccination, and a recent review indicated that VE against for symptomatic COVID-19 disease decreased by 24.9 percentage points among all ages from 1 month to 6 months after full vaccination. It can be difficult to disentangle potential changes in VE by time since vaccination from changes in VE that are due to circulation of different variants over time. The I-MOVE-COVID-19 and European Centre for Disease Prevention and Control (ECDC) networks in Europe carry out COVID-19 VE studies, including a VE study at primary care/community level. All studies are based on a common generic protocol.
We conducted a study in symptomatic individuals swabbed for a COVID-19 test at primary and care/community level in July and August 2021, assuming that any identified COVID-19 cases were infected with the Delta variant given its dominance in Europe during this period. We estimated VE against SARS-CoV-2 symptomatic infection, by vaccine brand, age group and time since vaccination to understand if there may be waning of vaccine-induced protection over time.
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Kissling, E., Hooiveld, M., Martínez-Baz, I., Mazagatos, C., William, N., Vilcu, A., Kooijman, M., Ilić, M., Domegan, L., Machado, A., de Lusignan, S., Lazar, M., Meijer, A., Brytting, M., Casado, I., Larrauri, A., Murray, J., Behillil, S., de Gier, B., Mlinarić, I., O'Donnell, J., Rodrigues, A., Tsang, R., Timnea, O., de Lange, M., Riess, M., Castilla, J., Pozo, F., Hamilton, M., Falchi, A., Knol, M., Filipović, S., Dunford, L., Guiomar, R., Cogdale, J., Cherciu, C., Jansen, T., Enkirch, T., Basile, L., Connell, J., Gomez, V., Martin, V., Bacci, S., Rose, A., Celentano, L., Valenciano, M. & teams, I. 2022, '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 2021', Eurosurveillance, 27(21). https://doi.org/10.2807/1560-7917.ES.2022.27.21.2101104