GVDN AESI Background rates 2015–2020

Before the unprecedented global rollout of COVID-19 vaccines, a list of adverse events of special interest (AESI) was developed based on the pathophysiology of SARS-CoV-2 infection and what was known about vaccine safety issues in general. Post vaccination rollout, further events have been added in response to the safety signals of thrombosis with thrombocytopenia syndrome and myocarditis, respectively.

The estimation of background and post-vaccination rates is a rapid and useful tool for the surveillance of vaccine AESI. In the context of a global collaboration, estimation of background rates is feasible for many countries since only outcome and population estimates as denominator are required. Background rates provide important context for regulatory and public health agencies to quickly assess emerging safety signals. Countries with access to immunisation registers can also provide post-vaccination rates, which allows for observed versus expected comparisons of AESI. Such comparisons have the potential to investigate early safety concerns, inform vaccination policies and can be conducted rapidly; well before a more sophisticated analysis can be planned and carried out.

One highly relevant example of this approach was the thrombosis with thrombocytopenia signal, which prompted the suspension of the use of Oxford/AstraZeneca COVID-19 vaccine on 11 March 2021 in Denmark and Norway. Immediately, a  collaboration between Denmark and Norway was formed to provide observed versus expected comparisons for a range of thrombotic events based on nationwide register data. The results showed an increased risk of serious thrombotic events primarily in the form of cerebral venous sinus thrombosis following vaccination with the adenoviral vector vaccine, corresponding to one case per ~40,000 vaccinations.1 On March 25, the vaccine was removed from the Danish programme. Norway similarly removed the vaccine from the national programme on May 12. Additional studies have confirmed this vaccine risk.

The GVDN Background Rates Dashboard below summarises background rates of adverse events of special interest (AESI) from different sites/countries and population subgroups (age and sex) on a set of consistently defined AESI outcomes over the six years (2015–2020) prior to the global SARS-CoV-2 virus (COVID-19 disease) outbreak. Contributing sites/countries followed the GVDN Background rates of adverse events of special interest following COVID-19 vaccination study protocol, and this harmonised approach to collection, collation, and analyses of the data allows comparison between sites/countries and aggregation of data for meta-analyses.

Click on this link to download the GVDN Background rates of adverse events of special interest following COVID-19 vaccination study protocol.

 Click here to view the paper Background rates of adverse events of special interest for COVID-19 vaccines: A multinational Global Vaccine Data Network (GVDN) analysis published in the journal Vaccine.

Eleven GVDN member sites followed the protocol above and analysed data from national or regional healthcare databases covering 197 million people from Europe, Asia, North and South America, and Oceania. The study captured data across five pre-pandemic years (2015–2019) and the initial year of the pandemic (2020).

You will need Adobe Acrobat Reader to open the study protocol.

Brief guide for using the dashboard

After selecting the site from a dropdown menu, data can be viewed in graph or table format by AESI and patient type as combined data, or by age, sex, or age-sex, and by year(s). Information describing the site, data source(s), active population, and patient type has been provided by each site and is available in the third tab.

To resize the dashboard to fit within your viewing screen, click in the dashboard area, then hold down the Control button on your keyboard and scroll up or down.

Clicking on the question icon beside each data set provides additional information related to the variables in that set. 

In the graph view, tab one, clicking on the camera icon will download a picture (PNG) file of the plot. It is possible to zoom into the plot, click and hold the right mouse button while drawing a marquee around the area of the plot you wish to zoom into, then release the button. Clicking on the house icon will reset the plot axes.  While in the graph view, hovering the mouse over a data point will show the closest data numerically.

Data provided in the table view, tab two, can be downloaded as a spreadsheet (XLXS) file by clicking on this button .

In tab three, information describing the site, data source(s), active population, and patient type has been provided by each site.

The data dashboard will time-out and the screen will become grey if the dashboard is left idle for too long. Refreshing the webpage will activate the dashboard again, previous data selections will need to be re-entered.


1. Pottegard A, Lund LC, Karlstad O, Dahl J, Andersen M, Hallas J, et al. Arterial events, venous thromboembolism, thrombocytopenia, and bleeding after vaccination with Oxford-AstraZeneca ChAdOx1-S in Denmark and Norway: Population based cohort study. BMJ. 2021;373:n1114.