The numbers we know about the AstraZeneca vaccine

The numbers we know about the AstraZeneca vaccine

The suspension is the result of a political choice, explains AIFA, linked to the blocking of vaccination in other countries. To date, there are 30 cases out of 5 million vaccinated in Europe: lower numbers of statistical cases (not due to the vaccine) expected among the population. But it is good to keep the precaution

(Photo: Getty Images) The news that the AstraZeneca vaccine has also been suspended in Italy by the Italian Medicines Agency (Aifa) "as a completely precautionary and temporary" affects the our attention and raises many questions, from how long the stop will last to whether and when people already vaccinated with AstraZeneca will receive the second dose. For now we do not have certain answers but we can shed some light on the reasons for the suspension and the statistical incidence of thrombotic events such as those reported so far. Meanwhile, the World Health Organization indicates that the distribution of the AstraZeneca vaccine will proceed undisturbed and has urged countries not to suspend vaccination campaigns. Here's what we know.

Aifa: why the vaccine was suspended

Today March 16 Nicola Magrini, director of Aifa, declared in an interview with Repubblica that it was a "Political choice", linked to the previous suspension of the AstraZeneca vaccine by other European countries, including France and Germany. Those who have already received the first dose, adds Magrini, need not worry and simply report any symptoms to the doctor, remembering that adverse reactions occur in the hours immediately following administration. To date, as Aifa recalls, no cause-effect link has been proven between vaccination and these events and for now there is only a temporal relationship. Given the importance of the case, the health authorities are working to understand the actual causes of this phenomenon.

The role of pharmacovigilance

In other words the question is: is this a statistical coincidence, given that every year there are several cases of thrombosis, or is it really a very rare associated effect to vaccines, which, remember, protect against Covid-19 whose risk of complications and death is much higher? In this sense, pharmacovigilance is working very well and we have real-time data on adverse events: for example, the page of the Drug Safety Reasearch Unit, an independent US unit that analyzes the safety and risk management of drugs, lists the cases of thrombocytopenia associated with thrombosis reported in people vaccinated in the US, Europe and the UK.

Europe and Italy, here are the data

Checks and counts of thrombotic events, in particular brain, in people who have been given the vaccine are ongoing. The European Medicines Agency (EMA) announces that as of 10 March 2021 there were 30 cases out of 5 million (or 0.6 cases out of 100 thousand) of vaccinations with the AstraZeneca vaccine. To better interpret the data, one wonders if these data are in line with the statistical incidence of this disease. In this sense, the Italian Association of Epidemiology (AIE) responds, which has taken a position on the suspension in Italy of the AstraZeneca vaccine.

The Association has explained that, on the basis of scientific studies and data on hospitalizations, every year in the population between 35 and 70 years, about 80 cases of deep vein thrombosis are expected (the one that also concerns today's cases) per 100 thousand people. This estimate corresponds to about 1.5-2 cases per week and 6 to 8 cases per month. As of March 14, almost 800 thousand Italians have received the AstraZeneca vaccine: there are 184 thousand vaccinated among the armed forces and 610 thousand among school staff. On the basis of previous statistics (6-8 cases out of 100 thousand for each month), within a month, among the 800 thousand vaccinated, 42-64 cases of thrombosis should have occurred as a result of the case. "These cases - writes the AIE - certainly occur not as a result of the vaccine but as a result of the normal incidence of the disease". In short, the numbers would be in line, at least at a statistical level, with the normal occurrence of thrombosis in the same sample of people. There is no "increase in cases of blood thrombi" among those who have received the vaccine, Professor Andrew Pollard, head of the research project from which the AstraZeneca vaccine was born, also points out to the BBC. Obviously the AIE itself limits itself to reporting data and does not indicate with certainty that it is a statistical coincidence.

Europe and the USA: the other cases

To date there are several countries that have suspended the AstraZeneca vaccine, including Germany, France, Spain. In Germany, data indicate that out of 1.6 million vaccinated there were 7 cases of cerebral venous sinus thrombosis, a rare form of thrombosis affecting the brain. The figure is a little higher than the annual incidence estimates - the cases that would occur anyway - equal to 3-4 cases per million people. But these cases would not only concern the AstraZeneca vaccine: on February 8, the New York Times reported 36 cases of autoimmune thrombocytopenia (or thrombocytopenia, platelet deficiency) associated with cerebral hemorrhage out of a total of 31 million vaccinated in the USA with the vaccines of Pfizer-BioNTech and Moderna - a disease which, however, has an incidence that falls within the statistics of the United States. In any case it is good to clarify and the authorities are investigating.

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