17 April 2021 — Swiss Policy Research
A new study by the University of Oxford reports that the risk of cerebral venous thrombosis (CVT, i.e. blood clots in the brain) after covid vaccinations is about 8 to 10 times lower than after covid disease (4 to 5 per million vs. 39 per million). Moreover, the study indicates that the risk of CVT is in fact similar after AstraZeneca (adenovector) and after Pfizer and Moderna (mRNA) vaccines.
But the study overestimates the CVT risk after covid, because the analysis was based on a US health records network comprising “hospitals, primary care, and specialist providers”, whereas most people with mild covid don’t visit a doctor or a hospital. Furthermore, the study underestimates the CVT risk after vaccinations, because it included everyone who had received “a first dose of the vaccine”, whereas side effects are generally more severe after the second dose.
Adjusting for these two biases, the CVT risk after full vaccination is equal to or higher than the risk after covid itself. The main difference is that CVT caused by covid affects primarily older people with more comorbidities (as the Oxford study confirms), whereas CVT caused by vaccines affects also, and perhaps even more so, young and healthy people (which is why it was noticed). In other words, the vaccines may cause symptoms of severe covid in young people at very low risk of severe covid.
In addition, confirmed cerebral venous thrombosis is not at all a major cause of post-vaccination death. The major causes of post-vaccination deaths, according to official reporting systems, are ‘general disorders’, ‘cardiac disorders’ (e.g. heart failure, heart attacks), ‘nervous system disorders’, and ‘respiratory disorders’ (e.g. blood clots in the lung).
Conclusion: Covid vaccines are generally effective, at least against current virus variants, but they are not mature medical products meeting the highest medical safety standards. There are already more than 5,000 post-vaccination deaths reported in the US and in Europe, and given underreporting and reporting backlogs, the real figure may be significantly higher. In Israel, an unexplained increase in all-cause mortality after the vaccination campaign has been observed.