Abstract

Estimating 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.

Rights

This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (https://creativecommons.org/licenses/by-nc/4.0/), which permits non-commercial re-use, distribution, and reproduction in any medium, provided the original work is properly cited. For commercial re-use, please contact journals.permissions@oup.com

Cite as

Kissling, E., Nunes, B., Hooiveld, M., Martínez-Baz, I., Monge, S., Robertson, C., Knol, M., Sève, N., Mlinarić, I., Domegan, L., Machado, A., Whitaker, H., Lazar, M., Meijer, A., Enkirch, T., Casado, I., Pérez-Gimeno, G., William, N., Enouf, V., Filipović, S., McKenna, A., Rodrigues, A., de Lusignan, S., Timnea, O., Latorre-Margalef, N., Castilla, J., Pozo, F., Hamilton, M., Masse, S., Ilić, M., Basile, L., O’Donnell, J., Guiomar, R., Riess, M., Popescu, R., Rose, A., Andrews, N., Bacci, S., Celentano, L., Valenciano, M., Moren, A., Beutels, P., Hens, N. & Rose, A. 2025, 'Recommendations for estimating and reporting vaccine effectiveness by time since vaccination: a COVID-19 case study', American Journal of Epidemiology, article no: kwaf254. https://doi.org/10.1093/aje/kwaf254

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Last updated: 03 December 2025
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