URGENT Japan: Watanabe et al.; "SARS-CoV-2 vaccine and increased myocarditis mortality risk: A population based comparative study in Japan"; remember, 'healthy vaccinee effect', deaths can be greater

by Paul Alexander

"SARS-CoV-2 vaccination was associated with higher risk of myocarditis death, not only in young adults but also in all age groups including elderly", healthy vaccinee effect, then risk 4 time higher




Japanese researchers looked at the vaccinated population e.g. 99 834 543 individuals aged 12 years and older who received SARS-CoV-2 vaccine once or twice by 14 February 2022. The reference population was defined persons aged 10 years and older from 2017 to 2019.

Key findings:

‘Number of myocarditis death which met the inclusion criteria were 38 cases. MMRR (95% confidence interval) was 4.03 (0.77 to 13.60) in 20s, 6.69 (2.24 to 16.71) in 30s, 3.89 (1.48 to 8.64) in 40s, respectively. SMR of myocarditis was 2.01 (1.44 to 2.80) for overall vaccinated population, 1.65 (1.07 to 2.55) for those 60 years or older. Estimated adMMRRs and adSMR were about 4 times higher than the MMRRs and SMR. Pooled MOR for myocarditis were 205.60 (133.52 to 311.94).’

“SARS-CoV-2 vaccination was associated with higher risk of myocarditis death, not only in young adults but also in all age groups including the elderly. Considering healthy vaccinee effect, the risk may be 4 times or higher than the apparent risk of myocarditis death. Underreporting should also be considered. Based on this study, risk of myocarditis following SARS-CoV-2 vaccination may be more serious than that reported previously.”

Healthy vaccinee effect where healthy persons use vaccines and do much better generally and frail persons, older are not given vaccines as much given that doctors do not see the benefit. May not benefit etc. This effect is pronounced when engaging in an observational type study and not the power of randomization to spread the confounders between the two comparative groups. This is the thinking though not a purist thinking but you should be guided. So consider that even with this confounder at play, that the risk of myocarditis was so clear for those vaccinated, then it is likely way higher. The researchers also stated this.

Issues to consider:

1)diagnosis of myocarditis death after SARS-CoV-2 vaccine is based on the physician’s diagnosis

2)since myocarditis after SARS-CoV-2 vaccine received media attention, it is likely that physicians paid more attention and reported more

3)SMR was only adjusted for age, MMRRs and SMRs were not adjusted for sex and for other cofounding factors such as calendar period, health care worker status, nursing home resident, and comorbidities

4)the Japanese researchers have no evidence on healthy vaccinee effect of SARS-CoV-2 vaccine in Japan, yet this is a strong issue to consider in any interpretation

5)this is more of an exploratory study yet the estimates are potent

6)met key criteria for causation (Hill) e.g. (1) temporarily, (2) consistency, (3) strength and (4) coherence of association.

7)massive baseline population, very large effect sizes, wide 95% CIs but consistent

SMR is the standardized mortality ratio and it is the ratio of observed to expected deaths