Read the numbers in context

There are two main ways researchers determine whether an adverse effffffffffffect is related to a vaccine, Ellenberg said. “One is understanding the biology and how the vaccine might potentially cause this, and the other is understanding whether this is happening more frequently than might be expected in the general population.”

Although there is no exact epidemiological data on the prevalence of coagulation disorders, incidence estimates in 2017 ranged from about 300 per 100,000 people per year to about 650 per 100,000 people per year, according to a draft report requested by the European Medicines Agency.

In the case of Astrazeneca’s vaccine, the drugmaker said in a statement Sunday that out of more than 17 million people who were vaccinated with the shots, there have been 15 events of deep vein thrombosis ( DVT) and 22 events of pulmonary embolism reported as of early March. These reports have led to a number of countries, including Germany, France and Italy, to pause use of the vaccine, despite European regulators and the World Health Organization still recommending Astrazeneca’s vaccine to prevent severe COVID- 19, the illness that can be caused by the novel coronavirus.

“Around 17 million people in the EU and UK have now received our vaccine, and the number of cases of blood clots reported in this group is lower than the hundreds of cases that would be expected among the general population,” Ann Taylor, Astrazeneca’s chief medical offifficer, said in the statement.