A big data study of 99 million people across eight countries showed greater than expected incidence of side effects from various Covid-19 vaccines, the Global Vaccine Data Network (GVDN) said on Monday.
The study, originally published in the medical journal Vaccine on February 12, looked at 13 neurological, blood, and heart-related conditions, called “adverse events of special interest.” Researchers looked at 99,068,901 vaccinated individuals from ten sites in eight countries.
“The size of the population in this study increased the possibility of identifying rare potential vaccine safety signals,” said Kristyna Faksova, the lead author of the study from the Statens Serum Institut in Copenhagen, Denmark.
According to the GVDN, the study observed a greater incidence of myocarditis (inflammation of the heart muscle) and pericarditis (inflammation of the heart sac) than expected among those who took the Pfizer/BioNTech (BNT162b2) and Moderna (mRNA-1273) shots.
Moderna’s vaccine also had a higher rate of acute disseminated encephalomyelitis (ADEM, inflammation and swelling in the brain and spinal cord), with seven observed events compared to two expected within 42 days of the first shot.
Safety signals for myocarditis were “consistently identified” following the first three doses of either mRNA shot, with the highest ratio after the second dose. Signals for pericarditis also appeared following the first and fourth doses of mRNA-1273 and were also observed after a third dose of the Oxford/Astra Zeneca (ChAdOx1) viral vector vaccine.
Recipients of ChAdOx1 had 190 observed events of Guillain-Barré Syndrome (GBS) compared to the expected 76, and 69 observed instances of cerebral venous sinus thrombosis (CVST, a type of blood clot in the brain) compared to the expected 21, the study has shown.
The GVDN has made the results available to the public on its interactive data dashboards, along with a warning not to read too much into correlations and that the vaccines are both safe and effective.
“By making the data dashboards publicly available, we are able to support greater transparency, and stronger communications to the health sector and public,” GVDN co-director Dr. Helen Petousis-Harris said.
The study was part of the GVDN’s Global COVID Vaccine Safety Project and was funded entirely by a $10 million grant from the US Centers for Disease Control and Prevention (CDC).