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. 2021 Jun 9;27(7):1290–1297. doi: 10.1038/s41591-021-01408-4

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© The Author(s) 2021

Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The images or other third party material in this article are included in the article’s Creative Commons license, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons license and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this license, visit http://creativecommons.org/licenses/by/4.0/.

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Extended Data Fig. 2 — Note: The line comes from a generalised additive Poisson model fitted to the number of cases with a simple spline term for the trend. Graph based upon data up to 22 March 2020. One of the assumptions of the standard self-controlled case series analysis is that the underlying rates of the event are constant over time. Fig. S2 shows the number of events for idiopathic thrombocytopenic purpura (ITP) since September 2019. A generalised Additive Poisson model was fitted to the daily data with a spline for the number of days since 1 September 2019 and a factor for the months. There was no evidence of any seasonal pattern associated with the months of the year (p = 0.189, using a change in deviance test) but there was evidence of a non-linear trend (p = 0.0138). Further investigation of the trend was undertaken by including binary change in level variables associated with the period post BNT162b2 (8 December 2020) and post ChAdOx1 (5 January 2021) This showed that there was no residual increasing trend (p = 0.58), nor any change in level following the introduction of BNT162b2 (p = 0.4315) but there was evidence of a change in level amounting to an 0.44 (95% CI 0.20, 0.68; p = 0.0003), additional events per day in the period after the introduction of the ChAdOx1 vaccine.