Norwegian and Danish researchers published a register study in BMJ of over 281,000 people who have received the AstraZeneca vaccine. – The study confirms previous findings from OUS and internationally.

The registry study finds 11 additional cases of venous thrombosis among 100,000 vaccinated.  

The article that follows people who have received the AstraZeneca vaccine in Denmark and Norway can be read in the British Medical Journal.

The British Medical Journal includes also a linked Editorial confirming that vaccination remains overwhelmingly the safest option.

The researchers conclude that even though a higher risk of venous thrombosis was observed, the benefit-risk assessment must be made based on the situation in each country and the benefits of using the vaccine. Among other things, one must consider the degree of control of the pandemic and the availability of other vaccines.

– This is a register study of 281,000 people aged 18-65 in Norway and Denmark, following the vaccinated for four weeks, and comparing the incidence of heart and cardiac diagnoses in the registers against what is the expected incidence in the general population. The Authors found an increased incidence of venous thrombosis, and especially in the veins of the brain in the people they followed.

Corresponds with previous findings
The study followed 148,792 people in Denmark, with a median age of 45 years and 132,472 in Norway, with a median age of 44 years. 80 and 78 percent in the cohorts were women, respectively. 

– This is in line with the findings of Holme and colleagues in the New England Journal of Medicine. We find in the registers the serious side effects that were mentioned in the study from Tromsø and Oslo University Hospital. In our study, we also include Danish data and also look at a number of other cardiovascular events.

– We find no increase in blood clots in the arteries or in the incidence of heart or brain infarction. However, we find an increased incidence of venous thrombosis (blood clots) in general, and there was also some increase in bleeding and low platelets. Although the risk of these outcomes is increased among vaccinated people, the number of incidents we found in the registers is low.

This article shows the much-discussed research finding from OUS Rikshospitalet, that vaccination with ChAdOx1 nCoV-19 in five patients seemed to induce a syndrome similar to autoimmune heparin-induced thrombocytopenia, vaccine-induced immune thrombotic thrombocytopenia (VITT), consisting of low platelets, blood clots and bleeding.

– We find signals for all this in the register study. VITT does not have its own diagnostic code in the health registers and we can therefore not calculate the number of cases of this directly. In this sense, what we find in the register data corresponds to what one might expect, based on reported incidents.

Tendency to bleed
In addition to low platelets and bleeding, they also found a tendency for an increased incidence of cerebral haemorrhages, and other haemorrhages such as nosebleeds. However, not all of these findings persisted when they excluded outpatient consultations.

Such registry studies are important for monitoring the signs of side effects after vaccination. It is important to be able to both confirm and deny signals.

– Here we see another example of how contemporary Norwegian and Danish health registers are useful during the pandemic. This is information that is important for the authorities when they make their decisions so that these are based on the best possible knowledge.

Risk must be assessed
The Authors do not believe the increased risk of blood clots necessarily provides an answer as to whether the vaccine should be used or not, because this must always be assessed on the basis of the current situation.

– In each individual country, the benefit of the vaccine must be weighed against the risk. The number of cases of serious side effects, degree of control of the epidemic, and access to alternative vaccines will be factors that can be emphasized. In Norway, we observed several serious side effects in a short time while keeping the epidemic under reasonable control.

EMA in its assessment of the vaccine , also points out that risk-benefit assessments must be based on how much infection there is of the virus in a country.

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