Japanese study misrepresented in posts claiming “heart failure surges among Covid-vaccinated”

Key takeaway

Myocarditis is the inflammation of the heart muscle. While COVID-19 mRNA vaccines are associated with rare cases of myocarditis, particularly in young males, COVID-19 itself is associated with a greater risk of myocarditis, along with other complications like blood clots. On balance, the benefits of the vaccines outweigh their risks.

Reviewed content

Verdict:

Inaccurate

Claim:

“Japan sounds alarm as heart failure surges among Covid-vaccinated”

Verdict detail

Misrepresents source: The study cited in support of this claim examined myocarditis cases reported after COVID-19 mRNA vaccination. But it didn’t report any alarming trends and the study doesn’t mention heart failure.

See our method of evaluation

Full Claim

“Japan sounds alarm as heart failure surges among Covid-vaccinated”; “Japan Sounds Alarm as Heart Failure Surges 4900% Among Covid-Vaxxed”

In February 2025, viral social media posts appeared, claiming that “Japan sounds alarm as heart failure surges among Covid-vaccinated”. These posts shared what appeared to be a screenshot of an article’s headline. One example was posted by the Facebook page KAG Save America 2024, which received more than 17,000 user engagements and more than 10,000 shares. Another example was this TikTok video, viewed more than 209,000 times.

The link shown in the image takes one to this study, published in the Journal of Infection and Chemotherapy, titled “SARS-CoV-2 mRNA vaccine-related myocarditis and pericarditis: An analysis of the Japanese Adverse Drug Event Report database”.

We were unable to find an article carrying the same headline shown in these posts, but we did find this article by Slay News, published on 18 January 2025, with a similar headline: “Japan Sounds Alarm as Heart Failure Surges 4900% Among Covid-Vaxxed”. This article also referenced the same study.

The Slay News article was shared on X by accounts with large followings, such as Patrick Soon-Shiong, the owner of the Los Angeles Times who’s endorsed U.S. Department of Health and Human Services (HHS) secretary nominee RFK Jr.; Jim Ferguson, a former candidate for the Brexit Party in the 2019 UK General Elections who’s spread vaccine misinformation; and Mary Talley Bowden, an otolaryngologist who spread COVID-19 and vaccine misinformation.

But the study doesn’t support the claim, and the scientific evidence shows that on balance, COVID-19 vaccination reduces the risk of complications from the disease, including heart complications. We explain below.

What did the study do and what did it find?

The study examined the Japanese Adverse Drug Event Report database, which is the Japanese equivalent of the U.S. Vaccine Adverse Event Reporting System (VAERS). Like VAERS, this database collects information about adverse events occurring after vaccination. And like VAERS, a report alone isn’t sufficient evidence that a vaccine caused an adverse event.

Examining data from April 2004 to December 2023, the researchers found 880,999 adverse event reports following COVID-19 mRNA vaccination, of which 1,846 were myocarditis and 761 were pericarditis. The data showed that most affected individuals were male and aged 30 years or below. The period between vaccination to onset of symptoms was eight days and below. These findings are consistent with that of previous studies that found an association between COVID-19 mRNA vaccines and myocarditis^[1-3].

The researchers concluded that “In the Japanese population, SARS-CoV-2 mRNA vaccination was significantly associated with the onset of myocarditis/pericarditis […] although most adverse events occurred early after vaccination, overall outcomes were good”. The study didn’t report any alarming trends, contrary to the implications in the posts.

Study didn’t look at heart failure; benefits of vaccines outweigh their risks

Contrary to the claim in the posts, the study was unrelated to heart failure, a condition in which the heart no longer pumps blood as well as it should. Myocarditis, on the other hand, is inflammation of the heart muscle, and it isn’t the same as heart failure. Heart failure can be a complication of myocarditis, but it’s important to note that myocarditis associated with COVID-19 vaccination is typically mild. Most patients go on to make a full recovery after rest and medication.

Furthermore, the study didn’t account for whether affected individuals had COVID-19 or other viral infections before developing myocarditis. This is important because one of the most common causes of myocarditis is infection by a virus, like those that cause the flu and the common cold. This is one reason the study cannot reliably assess whether myocarditis cases were actually caused by the COVID-19 mRNA vaccines.

Studies have shown that compared to COVID-19 vaccination, COVID-19 is associated with a greater risk of myocarditis, along with other complications like blood clots^[4-8]. The American Heart Association considers the benefits of the COVID-19 vaccines to outweigh their risks. An expert consensus by the American College of Cardiology found that “a very favorable benefit-to-risk ratio exists with the COVID-19 vaccine for all age and sex groups evaluated thus far”^[9].

Conclusion

Social media posts misrepresent a Japanese study about adverse events following COVID-19 vaccination, falsely claiming it showed heart failure is surging in vaccinated people. The study examined myocarditis cases following COVID-19 vaccination, but its findings are consistent with those reported in previous studies, and it didn’t mention heart failure.

While COVID-19 mRNA vaccines are associated with rare cases of myocarditis, particularly in young males, COVID-19 itself is associated with a greater risk of myocarditis, along with other complications. On balance, the benefits of the vaccines outweigh their risks.

REFERENCES

• 1 – Barda et al. (2021) Safety of the BNT162b2 mRNA Covid-19 Vaccine in a Nationwide Setting. New England Journal of Medicine.
• 2 – Hippisley-Cox et al. (2021) Risk of thrombocytopenia and thromboembolism after covid-19 vaccination and SARS-CoV-2 positive testing: self-controlled case series study. BMJ.
• 3 – Knight et al. (2022) Association of COVID-19 With Major Arterial and Venous Thrombotic Diseases: A Population-Wide Cohort Study of 48 Million Adults in England and Wales. Circulation.
• 4 – Block et al. (2022) Cardiac Complications After SARS-CoV-2 Infection and mRNA COVID-19 Vaccination — PCORnet, United States, January 2021–January 2022. Morbidity and Mortality Weekly Report.
• 5 – Patone et al. (2022) Risks of myocarditis, pericarditis, and cardiac arrhythmias associated with COVID-19 vaccination or SARS-CoV-2 infection. Nature Medicine.
• 6 – Writing Committee. (2022) 2022 ACC Expert Consensus Decision Pathway on Cardiovascular Sequelae of COVID-19 in Adults: Myocarditis and Other Myocardial Involvement, Post-Acute Sequelae of SARS-CoV-2 Infection, and Return to Play: A Report of the American College of Cardiology Solution Set Oversight Committee. Journal of the American College of Cardiology.