  We describe several shortcomings of a study by Patone et al, whose findings
were recently published in the American Heart Association Journal Circulation,
including the following:
  * The study's principal conclusion, as initially stated, begins "Overall, the
risk of myocarditis is greater after SARS-CoV-2 infection than after COVID-19
vaccination ...." However, Patone et al never attempt to assess the incidence
of myocarditis in their study population following SARS-CoV-2 infection.
Rather, they make an untenable assumption that all infections occurring in
their study population are associated with (reported) positive COVID-19 tests.
Using publicly available data from the UK's ONS and NHS, we show that Patone et
al's estimates, for the unvaccinated, of myocarditis incidence associated with
infection are likely overestimated by a factor of at least 1.58.
  * The method Patone et al use to compute the incidence of myocarditis among
the unvaccinated after a positive COVID test may overestimate risk. The authors
assume, without justification, that unvaccinated persons hospitalized during
the study period with positive-test-associated myocarditis would later choose
to vaccinate with the same probability as unvaccinated persons who have had a
positive COVID test. We present a plausibility argument that suggests a
possible further exaggeration of myocarditis risk post infection by a factor of
1.5.
  * Patone et al fail to discuss important limitations of their study with
respect to guiding public health recommendations. For instance, an
insignificant number of cases contributing to the study's findings were
Omicron-variant cases. Thus, the study's estimates of myocarditis risk
following infection do not speak to the risk following Omicron infection, which
is recognized to be milder than that of previous variants.
