Rare cases of cerebral thrombosis possibly linked to AstraZeneca’s vaccine have been enough to send health officials into a panic. However, such occurrences are much more common in patients infected with Covid-19. This puts the risk-benefit ratio into perspective.
Rare cases of cerebral thrombosis
The few cases of atypical thrombosis reported after AstraZeneca and Johnson & Johnson vaccines have led to strict restrictions on their use. A precautionary step that is completely unnecessary, according to a new study from the University of Oxford. According to the study, the risk of getting a blood clot in the brain is ten times higher after catching Covid-19 than after vaccination.
The researchers studied the incidence of cerebral thrombosis in two groups of patients who either had Covid-19 disease or had been vaccinated with an mRNA vaccine (Pfizer or Moderna) or a vaccine from AstraZeneca. Incidence rates were as follows:
- 39 thrombosis cases per million for patients infected with Covid-19.
- 4 cases per million for vaccines from Pfizer and Moderna.
- 5 cases per million after the first dose of AstraZeneca’s vaccine.
Thus, the risk of thrombosis from Covid-19 is 10 times higher than for Pfizer’s vaccine and 8 times higher than for AstraZeneca’s vaccine.
This leads to two important conclusions, says Paul Harrison, professor of psychiatry and head of the neurobiology group at Oxford University. “First, Covid-19 significantly increases the risk of cerebral venous thrombosis, an addition to the list of many already known complications of the virus. Second, the risk of thrombosis is much higher with Covid-19 than with current vaccines.”
A favorable risk-benefit ratio
It should be noted that the risk of AstraZeneca’s vaccine as determined in this study is two times lower than the risk estimated by the European Medicines Agency (1 in 100,000, or 10 cases per million). But either way, this is still much lower than the risk of getting Covid-19, even in people under 30, points out Paul Harrison, who suggests that age-related limitations have no reason to exist.
We’re only talking about the risk of thrombosis here. But when we consider all the other possible complications of Covid-19 infection (including death!), the potential clotting problems associated with the vaccine “seem insignificant,” says John Bell, another Oxford researcher interviewed by Sky News.
More such comparisons can be made. For instance, the risk of venous thrombosis with the 3rd generation birth control pill is 3 to 4 cases per 10,000, 10 times higher than with anti-covid vaccination (taking into account all types of venous thrombosis).
Acetaminophen (Tylenol) is also the cause of thousands of acute poisonings every year in the US. However, no one has thought of banning it, although it is used to treat often more benign diseases.