Norwegian-Danish study of rare side effects in connection with AstraZeneca vaccination published
Together with researchers in Denmark, the Norwegian Institute of Public Health has studied the extent of side effects associated with the AstraZeneca vaccine. The study shows an increased rate of rare but serious blood clots in the brain and venous blood clots.
Following the initial reports of rare side effects after vaccination with the AstraZeneca vaccine (Vaxevria), a registry study was initiated quickly. The study includes over 281,000 people who have received this vaccine in Norway and Denmark. It is the first study to systematically investigate the occurrence of side effects in the cardiovascular system after vaccination.
“This is a comprehensive study that has been conducted quickly and with high quality. The excellent collaboration with Danish researchers has been of vital importance,” says Hanne Løvdal Gulseth, Department Director at the Norwegian Institute of Public Health.
Side effects in first 28 days after vaccination studied with data from health registries
All hospital visits were mapped for 281,264 people aged between 18 and 65 years who had been vaccinated with the AstraZeneca vaccine. For each diagnosis, the number of observed cases among those vaccinated was compared with the number expected in the general population.
The results show that there were increased rates of venous blood clots in the brain (cerebral venous thrombosis) in the first 28 days after vaccination. The researchers found that one additional case occurred for every 40,000 vaccinated. The risk of venous thrombosis (blood clots) in general was also increased by about one additional case for every 9,000 vaccinated. There was no increase in blood clots in the arteries or in the incidence of heart attacks or strokes. The incidence of haemorrhages and low platelet counts was also slightly increased. Although the risk of side effects is increased, the number of events found in the registries is low. The risk for each individual person who has been vaccinated is therefore still considered to be low.
“Norway and Denmark have good health registries that are of high quality and updated. We are therefore in a privileged position of having continuous access to current, reliable and privacy-protected knowledge about the effect and side effects after vaccination. Such studies are important to confirm or disprove suspected adverse reaction signals from spontaneous adverse event reports. Reliable data about the background occurrence of the relevant conditions are important for putting the findings in context,” explains Gulseth.
Use of vaccine must be based on an overall assessment
The results from the work have been shared continuously with the Norwegian, Danish and international authorities and were included in their assessments about the use of the AstraZeneca vaccine.
“There is no contradiction between our findings and the European Medicines Agency's (EMA) assessment of the vaccine. Although rare, severe side effects can occur, the EMA has stated that the overall benefit of the vaccine outweighs the risk,” says Gulseth.
Gulseth points out that COVID-19 is a severe disease, and each country must therefore make their own assessment of the benefits of the vaccine compared to the risk of possible side effects. The assessment must be based on the situation in each country, such as the number of cases of severe side effects, the degree of control of the epidemic, and access to alternative vaccines.
On 11 March 2021, the Norwegian Institute of Public Health decided to temporarily pause vaccination with the AstraZeneca vaccine in Norway. The decision was made after reports of severe cases internationally, and a death in Denmark following vaccination. During the pause, there were also reports of similar cases and four deaths in Norway.
Cerebral venous thrombosis is a prominent feature of the new syndrome, known as 'Vaccine-induced Immune Thrombotic Thrombocytopenia' (VITT). This syndrome includes other severe side effects, such as large blood clots in veins from the gastrointestinal tract, liver and spleen.
In this study, both thrombosis (blood clots) and thrombocytopenia (low platelet count) were diagnoses that were more frequently found among vaccinated people, but this study has not studied VITT directly.
Following an overall assessment, the Norwegian Institute of Public Health has recommended not to use the AstraZeneca vaccine in the Norwegian Coronavirus Immunisation Programme. The Government will make the final decision on further use. Coronavirus vaccination has continued since March 11 using COVID-19 vaccines from BioNTech / Pfizer and Moderna.
Pottegård, A., (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 doi: https://doi.org/10.1136/bmj.n1114