One of the accepted side-effects of the Covid vaccines is increased risk of myocarditis. This risk was first identified in a leaked report produced for the Israeli Government, which was followed by several months of the denial of any link by the vaccine manufacturers and various governments until eventually the evidence for this side-effect became overwhelming and it was added to the growing list of official side-effects.
Of course, once a potential risk of myocarditis was identified there were some attempts by epidemiologists to sift though available data to try to identify the impact of this risk on the vaccinated population. The most recent paper to study this side-effect appeared in late August out of the Nuffield Department of Medicine in Oxford Radcliffe hospital by a team led by Julia Hippisley-Cox. This paper purports to show that the risk of myocarditis following vaccination is much lower than the risk following infection with Covid and that the risk of myocarditis following infection in the vaccinated is much lower than the risk in the unvaccinated. Thus the paper implies that the vaccines are appropriate to use even with this ‘rare’ side-effect. However, there are some complexities in the paper that warrant further attention.
My main concern with the Hippisley-Cox paper is that it is based on the results of a self-control study. With this methodology, the baseline data (i.e., the rate of myocarditis that you’d expect without the vaccines) are gathered from the same individuals as took the vaccine, only outside of the ‘risk window’ that is said to be associated with the vaccines. This methodology is well established and has many advantages, the most important of which being that so long as the study is well designed there is only a low risk of bias because the same group of individuals acts as its own control. The ‘so long as the study is well designed’ in the previous sentence is, however, crucial: pivotal in the design assumption is that the risk window contains all of the additional risk and that the risk returns to baseline outside of this window. If this condition doesn’t obtain then the incidence in the ‘control group’ will be elevated and this will reduce the apparent excess in the ‘treatment group’.
For the Hippisley-Cox paper the main assumption is spelt out in the methods section (emphasis added):
We defined the exposure risk intervals as the following prespecified time periods: 0, 1-7, 8-14, 15-21 and 22-28 days after each exposure date, under the assumption that the adverse events under consideration are unlikely to be related to exposure later than 28 days after exposure.
The pertinent question, then, is: is this assumption correct? Let’s have a look at the risks identified in the paper for the 28 days following the first dose of vaccine, split into four week periods.
Read More – Oxford Study Which Claims Myocarditis is Higher After Covid Than Vaccination is Flawed and Actually Suggests Vaccines Increase Risk by 30%.